Reference
Look up a storage term
A wiki-style reference for the words that show up when your phone, tablet, or Mac runs out of space. Each page answers one question, then links to the guides and tools that act on it.
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Storage concepts 68
The core vocabulary behind why a device fills up and what is safe to clear.
Storage conceptsAllocation unit (cluster size)An allocation unit, or cluster, is the smallest chunk of disk space a file system will give to a file. Even a 1-byte file occupies a whole cluster, so many small files waste space in the unused remainder, called slack space. Larger clusters speed up big files but waste more on small ones.Storage conceptsAPFSAPFS (Apple File System) is the default file system on modern iPhones, iPads, and Macs. It is built for flash storage and adds features like instant copies (clones), space-efficient snapshots, and strong encryption.Storage conceptsApp cacheAn app cache is temporary data an app stores to load faster — images, thumbnails, streamed media, and web content. Clearing it is safe: the app simply re-downloads what it needs the next time you use it.Storage conceptsAutofill dataAutofill data is the information a browser saves to fill forms for you — addresses, names, payment cards, and saved passwords. It uses almost no space; clearing it is a privacy and convenience choice, since the browser will stop suggesting those entries.Storage conceptsBad sectorA bad sector is a small region of a hard drive or storage device that can no longer reliably store data, due to physical damage or wear. The drive marks bad sectors so it stops using them; a growing number of them is a warning that the drive is failing.Storage conceptsBitrateBitrate is the amount of data used per second of audio or video, usually measured in megabits per second (Mbps). A higher bitrate carries more detail and produces a sharper result, but it also makes the file proportionally larger.Storage conceptsBloatwareBloatware is software pre-installed on a device by the manufacturer or carrier that you did not choose — trial apps, duplicate utilities, and promotional apps. It takes up storage and sometimes cannot be fully removed, only disabled.Storage conceptsBrowser cacheThe browser cache is a local copy of web page parts — images, scripts, stylesheets, and fonts — saved so pages reload faster on your next visit. Clearing it frees space and forces a fresh download, but never signs you out, since logins live in cookies instead.Storage conceptsBrowsing historyBrowsing history is the list of pages you have visited that your browser keeps for quick back-navigation, address-bar suggestions, and search. It uses little storage; clearing it is mainly about privacy and removes those suggestions, not your saved logins.Storage conceptsCache PartitionThe cache partition is a dedicated Android partition the system uses for temporary data, mainly OS update staging. It is separate from per-app cache and is wiped from recovery mode, not from in-app cleaning tools.Storage conceptsCached DataCached data is temporary files an app saves locally so it can reload content faster instead of re-fetching it. It includes downloaded images, thumbnails, web assets, and prefetched media. Cache is regenerable: deleting it frees space without losing accounts, settings, or your real documents.Storage conceptsCompression (lossy vs lossless)Compression shrinks a file by encoding its data more efficiently. Lossless compression rebuilds the original exactly, while lossy compression permanently discards detail the eye or ear is least likely to notice in exchange for much smaller files.Storage conceptsCookiesCookies are small text files a website stores in your browser to remember you between visits — keeping you signed in, holding cart items, and saving preferences. Clearing them frees a little space but signs you out of most sites and resets settings.Storage conceptsData units (KB, MB, GB, TB)Data units measure file and storage size, each roughly 1,000 times the last: a kilobyte (KB) is tiny text, a megabyte (MB) is a photo, a gigabyte (GB) is hundreds of photos or a short video, and a terabyte (TB) is about a thousand gigabytes.Storage conceptsDisk partitionA partition is a section of a physical drive that the operating system treats as a separate logical drive, each with its own file system. Partitioning lets one disk hold, for example, a system volume and a data volume, or two operating systems, while staying a single piece of hardware.Storage conceptsDownloaded Media CacheDownloaded media cache is the photos, videos, voice notes, and documents that chat and social apps save to the device when you receive or view them. Unlike pure cache, much of it is stored as full files in the app's folders, so it persists, accumulates, and is often the single largest reclaimable category.Storage conceptsDownloads folderThe Downloads folder is the default location where browsers and apps save files you download — PDFs, images, installers, and attachments. It quietly accumulates one-off files you rarely revisit, making it a fast win for freeing space.Storage conceptseMMC storageeMMC (embedded MultiMediaCard) is a type of built-in flash storage soldered into budget phones, tablets, and laptops. It uses the same flash technology as an SD card and is reliable but slower than the UFS or SSD storage found in higher-end devices.Storage conceptsEmpty FoldersEmpty folders are directories that contain no files (or only other empty subfolders). They take negligible space themselves but accumulate as leftover clutter after apps, downloads, or media are deleted, cluttering file managers and backups.Storage conceptsexFATexFAT is a lightweight file system designed for SD cards and USB flash drives. It works across Windows, macOS, Android, and most cameras, and — unlike FAT32 — has no practical 4 GB file-size limit, making it ideal for large videos.Storage conceptsExternal hard driveAn external hard drive is a storage drive in its own case that connects over USB to add space outside your computer or phone. It is a cheap way to offload large photo and video libraries and keep backups, freeing room on the device’s built-in storage.Storage conceptsFAT32FAT32 is an older file system with the widest compatibility — nearly every device and operating system reads it. Its key drawback is a hard 4 GB limit on the size of any single file, which makes it unsuitable for large videos or disk images.Storage conceptsFile systemA file system is the method a device uses to organize and track files on storage — naming them, recording where each one lives, and managing free space. Common ones include APFS (Apple), NTFS (Windows), and exFAT and FAT32 (cross-platform).Storage conceptsFlash storageFlash storage is the chip-based memory that holds files in phones, tablets, SSDs, SD cards, and USB drives. It has no moving parts, so it is fast and durable, and it keeps your data even when the device is powered off.Storage conceptsFormatted capacity (why 128GB shows less)Formatted capacity is the usable space a device actually reports, which is always less than the advertised number. The gap comes from two things: marketers count a gigabyte as 1,000,000,000 bytes while many systems count 1,073,741,824 (a GiB), and the operating system itself occupies part of the drive.Storage conceptsGame cache & downloadsGame cache and downloads are the temporary and stored files PC game launchers keep — download buffers, update files, shader caches, and pre-allocated install data. Much of it is reclaimable, but installed games and save files are not part of the clearable cache.Storage conceptsGB vs GiB (Binary vs Decimal)GB (gigabyte) and GiB (gibibyte) are two ways to count storage. A GB is defined as 1,000,000,000 bytes (decimal, 1000-based), while a GiB is 1,073,741,824 bytes (binary, 1024-based). Manufacturers label capacity in decimal GB, but phones often report it in binary, so a "128 GB" device shows less.Storage conceptsHDD (hard disk drive)An HDD (hard disk drive) stores data on spinning magnetic platters that a moving head reads and writes. It is slower than an SSD but much cheaper per gigabyte, which makes it a popular choice for large external drives and bulk archives.Storage conceptsIndexedDBIndexedDB is a structured, in-browser database that web apps use to store larger amounts of data on your device — offline content, cached records, and full app state. It can grow much larger than cookies or localStorage, and clearing a site’s data is how you reclaim it.Storage conceptsInodeAn inode is the data structure a Unix-style file system uses to store a file’s metadata — its size, permissions, timestamps, and the location of its data blocks — but not its name. Each file uses one inode, so a disk can run "out of inodes" even with free space if it holds millions of tiny files.Storage conceptsInternal storageInternal storage is the built-in, non-removable flash memory soldered inside a phone or tablet, where the operating system, apps, and your files live. Its size is fixed at purchase (for example 128 GB), and it is what fills up — not RAM and not a memory card.Storage conceptsJournaling file systemA journaling file system keeps a log (journal) of pending changes before writing them to disk, so an interrupted write — from a crash or power loss — can be rolled back or completed instead of leaving the drive corrupted. APFS, NTFS, ext4, and HFS+ all use journaling.Storage conceptsJunk filesJunk files are leftover data that no longer serves a purpose — app caches, temporary files, logs, crash reports, and remnants of deleted apps. Clearing them frees space safely because nothing you actively use depends on them.Storage conceptsLarge FilesLarge files are the biggest single items on your phone, usually videos, app downloads, archives, and document caches. Because a handful of them can occupy gigabytes, finding and reviewing large files is the fastest way to reclaim meaningful storage.Storage conceptsLeftover APK FilesLeftover APK files are Android app installer packages that remain in storage after an app is installed or updated. The installed app runs from the system, so the original .apk is just a copy you can usually delete to reclaim space.Storage conceptsLocal storage (localStorage)localStorage is a small per-site store where web apps save data that persists across visits and browser restarts — drafts, preferences, and tokens. Unlike a session, it does not expire on its own; clearing site data is how you remove it, which can reset or sign you out of that web app.Storage conceptsLow Storage WarningA low storage warning is the system alert your phone shows when free space runs critically low. Beyond the message, the device may block photos, app updates, and OS upgrades, and performance can suffer until you free up space.Storage conceptsMBR vs GPTMBR (Master Boot Record) and GPT (GUID Partition Table) are the two schemes that define how a drive is partitioned and booted. MBR is older and limited to 2 TB and four primary partitions; GPT is the modern standard, supporting far larger drives and many more partitions.Storage conceptsMemory card (SD/microSD)A memory card is a small, removable flash-storage card — full-size SD or the tiny microSD used in phones — that adds storage to a device or holds photos and video from a camera. Many Android phones accept one to expand space; most iPhones do not.Storage conceptsMessaging App StorageMessaging app storage is the total space a chat app occupies: the app binary plus its databases, caches, and downloaded media. Media dominates this figure, which is why apps like WhatsApp and Telegram routinely grow to several gigabytes and rank among the biggest storage consumers on a phone.Storage conceptsMobile Browser CacheThe mobile browser cache is local storage where Chrome, Safari, or other mobile browsers keep copies of web pages, images, scripts, and other site assets so repeat visits load faster and use less data. It can grow to hundreds of megabytes over time.Storage conceptsNTFSNTFS (NT File System) is the default file system for Windows drives. It supports very large files, file permissions, encryption, and journaling, but Macs can read NTFS drives without extra software while writing to them requires it.Storage conceptsOffline Map CacheAn offline map cache is the on-device store of map tiles, routing data, and downloaded regions that lets navigation apps work without a connection. It can grow to several gigabytes and is often counted as app data rather than user files.Storage conceptsOther / Misc storageOther (or Miscellaneous) storage is the cross-platform catch-all category for files that do not fit named buckets like Photos, Apps, or Media — mainly caches, logs, system files, and temporary data. Most of it is reclaimable, and it appears under different names across iOS, Android, and macOS.Storage conceptsPhone Storage FragmentationOn phones, "fragmentation" refers to free space and files being scattered across flash storage. Because phones use flash (not spinning disks), classic seek-time fragmentation barely matters; flash controllers and filesystems like F2FS handle placement, so manual defrag isn't needed.Storage conceptsPrefetch / preload cachePrefetch and preload caches hold pages and resources a browser downloads ahead of time, guessing what you’ll open next so it appears instantly. They are part of the browser cache, take temporary space, and clear with cached files — safe to remove anytime.Storage conceptsRAID (0/1/5/10)RAID combines multiple drives into one logical volume for speed, redundancy, or both. RAID 0 stripes data for speed with no protection; RAID 1 mirrors drives for safety; RAID 5 spreads data and parity to survive one drive failure; RAID 10 combines mirroring and striping.Storage conceptsResidual FilesResidual files are leftover data an app or process leaves behind after it finishes or is removed: orphaned caches, logs, empty config folders, and temp files no longer linked to a running app. They consume space without serving any active purpose.Storage conceptsService worker (offline cache)A service worker is a background script a website installs to serve pages and assets even offline, powering installable web apps (PWAs). It keeps its own cache of files; clearing a site’s data unregisters it and removes that cache, which can free space and disable offline access.Storage conceptsSession storagesessionStorage is a small per-tab store web apps use for data that should last only while a tab is open — form steps, temporary state, or a one-visit token. It clears automatically when you close the tab, so it rarely accumulates and almost never needs manual cleanup.Storage conceptsSite dataSite data is the umbrella term for everything a website stores on your device — cookies, localStorage, IndexedDB, and service-worker caches. It is what browsers list per site and what fills the storage a single site uses; clearing it removes all of those and resets the site.Storage conceptsSSD (solid-state drive)An SSD (solid-state drive) stores data on flash memory chips with no moving parts, so it reads and writes far faster than a spinning hard drive. SSDs are the standard internal storage in phones, tablets, and modern laptops, prized for speed, silence, and shock resistance.Storage conceptsSSD vs HDDSSDs use flash memory with no moving parts and are much faster but cost more per gigabyte; HDDs use spinning platters and are slower but far cheaper for large capacities. A common setup is an SSD for the system and apps, and an HDD for bulk media and backups.Storage conceptsStorage BottleneckA storage bottleneck is when nearly full or slow flash storage limits a device's overall performance. With little free space, the OS can't allocate cache, swap, or scratch files efficiently, causing lag, stutter, and slow app launches.Storage conceptsStorage optimizationStorage optimization is a feature that keeps full-resolution originals in the cloud while storing smaller, space-saving copies or previews on the device. You see and use your files normally, and the originals download on demand — so the device holds far less than the full library.Storage conceptsStorage vs RAMStorage is the permanent space that holds your photos, apps, and files even when the phone is off. RAM (memory) is the temporary working space apps use while running. Freeing storage and freeing memory are different jobs — and "RAM boosters" do not create storage.Storage conceptsStreaming App CacheStreaming app cache is the audio, video, and image data apps like Netflix, Spotify, and YouTube store on your device to play smoothly and load offline content. It is one of the largest, fastest-growing cache categories on a phone.Storage conceptsSwap partition / swap fileSwap is disk space the operating system uses as overflow for RAM. When physical memory fills, the system moves less-active data from RAM to a swap partition or swap file on disk, freeing memory for active work. It lets a device run more than its RAM alone would allow, but disk is far slower than RAM.Storage conceptsSystem Reserved StorageSystem reserved storage is space the operating system holds back from the user for updates, caches, and temporary files. It explains why a device shows less usable capacity than its advertised size and why 'System' appears in storage breakdowns.Storage conceptsSystem Update LeftoversSystem update leftovers are the downloaded installer packages, cached files, and temporary data an operating system creates to apply an OTA update, which can remain on a phone after the update finishes and consume storage that the system does not always reclaim promptly.Storage conceptsTemporary filesTemporary files are short-lived data an app or the operating system creates while working — during installs, downloads, edits, or printing. They are meant to be deleted automatically, but stalled tasks and crashes can leave them behind, taking up space.Storage conceptsThumbnail cacheA thumbnail cache is a store of small preview images that lets photo galleries, file browsers, and apps render grids instantly instead of rebuilding each preview from the full file. It is rebuildable data, so clearing it is safe — the system simply regenerates previews as needed.Storage conceptsTRIM (SSD)TRIM is a command that lets the operating system tell an SSD which blocks of data are no longer in use after a file is deleted, so the drive can erase them ahead of time. This keeps writes fast and helps the SSD last longer. It runs automatically on modern systems.Storage conceptsUFS storageUFS (Universal Flash Storage) is the high-speed flash storage built into most modern smartphones and many tablets. It is much faster than the older eMMC standard because it can read and write data at the same time, which speeds up app launches, downloads, and file transfers.Storage conceptsUSB flash driveA USB flash drive is a small, pocket-sized stick that stores data on flash memory and plugs into a USB port. It is a handy way to carry files between devices and offload smaller documents and photos, though it is slower and lower-capacity than an SSD or external hard drive.Storage conceptsUsed vs Available StorageUsed storage is the space already occupied by the OS, apps, and your files; available storage is what remains free for new data. The two add up to roughly the formatted capacity, which is always less than the advertised size.Storage conceptsVideo codec (H.264 vs H.265/HEVC)A video codec is the method used to compress and decompress video. H.265 (HEVC) is the newer successor to H.264 (AVC) and encodes the same quality in noticeably less space, which is why modern phones record in HEVC to keep video files smaller.Storage conceptsZero-Byte FilesZero-byte files are files whose content length is 0 bytes. They hold no data but still occupy a directory entry and inode/metadata, and they typically appear from interrupted downloads, crashed writes, placeholder/lock files, or failed app operations.
iPhone & iPad 19
iOS and iPadOS storage categories, settings, and behaviors.
iPhone & iPadAirDropAirDrop is Apple’s feature for sending photos, videos, and files wirelessly between nearby Apple devices. Received items are saved permanently — photos and videos go to Photos, other files to the Files app — so a busy AirDrop history quietly adds to your storage.iPhone & iPadApp ClipsAn App Clip is a small, instant piece of an app that runs without a full install — for tasks like paying for parking or renting a scooter. App Clips are intentionally tiny and are removed automatically after a period of disuse, so they rarely affect storage.iPhone & iPadApp LibraryApp Library is the auto-organized screen at the end of your Home Screen pages that holds every installed app in category folders. It is purely an organizer — apps there take the same storage whether or not they also sit on a Home Screen page.iPhone & iPadApp thinningApp thinning is how the App Store delivers only the parts of an app your specific device needs — the right graphics, code, and resources — so the installed download is smaller than the full app bundle. It happens automatically and is handled by Apple, not by you.iPhone & iPadBooks & PDF storageBooks and PDFs you add to Apple Books or save in the Files app are stored on your device and can grow large — illustrated books, audiobooks, and scanned PDFs especially. They sync through iCloud, but local copies still count toward your iPhone storage.iPhone & iPadDocuments & DataDocuments & Data is the storage an app accumulates on top of its install size — downloads, saved files, login state, and cached media. It often dwarfs the app itself, which is why a small app can occupy several gigabytes.iPhone & iPadFamily SharingFamily Sharing lets up to six people share purchases, subscriptions, and an iCloud+ storage plan while keeping separate accounts. Shared iCloud+ storage is pooled across the family, but each person’s photos and files stay private and count toward the shared total.iPhone & iPadFind MyFind My is Apple’s service for locating your devices, AirTags, and shared friends and family on a map, and for locking or erasing a lost device. It runs in the background using almost no storage and is separate from iCloud storage space.iPhone & iPadHealth App DataHealth App Data is the personal health and activity history — steps, workouts, heart rate, sleep, and more — stored by Apple’s Health app. It is encrypted, can sync through iCloud, and is not recoverable once deleted, so it should be treated as irreplaceable.iPhone & iPadiCloud KeychainiCloud Keychain is Apple’s built-in password manager that syncs your saved passwords, passkeys, Wi-Fi credentials, and payment card details across your devices, end-to-end encrypted. It uses negligible storage and does not count against your iCloud space.iPhone & iPadiOS Update SpaceiOS Update Space is the room an iOS software update needs — both the downloaded installer and the temporary working space to apply it. A downloaded update that has not been installed sits in storage and can show up inside System Data.iPhone & iPadMail StorageMail Storage is the space the iOS Mail app uses for messages and, mainly, the attachments it downloads to view them offline. Most of it is a cache: deleted attachments simply re-download from the mail server when you reopen the message.iPhone & iPadOffload AppOffloading an app removes the app itself to free space but keeps its documents and data, so reinstalling restores everything where you left off. Deleting an app removes both the app and its data permanently.iPhone & iPadOn-Demand ResourcesOn-Demand Resources (ODR) let an app download content — game levels, tutorials, or extra assets — only when needed, instead of bundling everything in the initial install. iOS can purge this downloaded content automatically when storage runs low.iPhone & iPadOptimize iPhone StorageOptimize iPhone Storage is an iCloud Photos setting that keeps smaller, device-sized versions of your photos and videos on the phone while the full-resolution originals stay in iCloud. The full file re-downloads on demand when you open or share it.iPhone & iPadRecently DeletedRecently Deleted is a holding area that keeps photos, videos, files, or messages for about 30 days after you delete them, so they can be recovered. The space is not freed until this folder is emptied or the 30 days pass.iPhone & iPadSafari Website DataSafari Website Data is the cache, cookies, and local files websites store on your device to load faster and remember you. Clearing it is safe and reclaims space, but it signs you out of sites and removes saved browsing state.iPhone & iPadShared with YouShared with You automatically surfaces content sent to you in Messages — photos, links, music, and articles — inside the matching app. Photos shared this way can be saved into your library, where they then count toward your storage like any other image.iPhone & iPadSystem DataSystem Data (shown as "Other" on older iOS) is the catch-all storage category for caches, logs, Siri voices, system files, and temporary data that does not fit Photos, Apps, or Media. Most of it is reclaimable cache that iOS clears automatically when space runs low.
Android 19
Android storage, cache, and file-management concepts.
Android.nomedia fileA .nomedia file is an empty marker file that tells Android’s media scanner to skip a folder, so its photos, videos, and audio do not appear in the Gallery or music apps. It hides media from view but does not delete it or free any storage.AndroidAdoptable storageAdoptable storage is an Android feature that formats a microSD card to act as internal storage. The card is encrypted and tied to that one device, so it stops being portable and cannot be read elsewhere.AndroidAndroid/data folderThe Android/data folder holds app-specific files — caches, downloaded content, and saved data — that each app keeps outside its private storage. It can grow to many gigabytes and is largely off-limits to file managers on modern Android due to scoped storage.AndroidClear Data vs Clear CacheOn Android, Clear cache deletes only an app’s temporary files and is safe. Clear data (Clear storage) wipes the app back to a fresh-install state — settings, logins, and saved files all go, so you are signed out.AndroidDalvik/ART cacheThe Dalvik/ART cache holds the optimized, precompiled machine code Android generates from your installed apps so they launch faster. It is managed by the system, rebuilt automatically, and not something you clear by hand to free space.AndroidDevice CareDevice Care is Samsung’s built-in maintenance hub on Galaxy phones, covering battery, storage, memory, and device protection in one place. Its storage section finds large files, duplicates, and cache so you can clear them without extra apps.AndroidFiles by GoogleFiles by Google is Google’s free file manager and cleanup app for Android. Its Clean tab suggests junk files, duplicate photos, and large or unused files to remove, and deleted items go to a Trash that holds them for 30 days.AndroidGboard storageGboard storage is the space Google’s keyboard uses for downloaded languages, learned-word and prediction data, stickers, GIFs, and emoji caches. It can quietly reach hundreds of megabytes, and most of it is safe cache you can clear.AndroidGoogle OneGoogle One is Google’s paid subscription that expands the 15 GB of free storage shared across your Google Account. The extra space is pooled across Google Drive, Gmail, and Google Photos — it is cloud storage, not space on your phone.AndroidGoogle Photos storageSince June 1, 2021, photos and videos backed up to Google Photos count against the 15 GB of storage shared across your Google Account. The old free, unlimited “High quality” backup ended on that date.AndroidInternal vs external storageInternal storage is the built-in flash memory soldered into an Android phone, where the system, apps, and most files live. External storage means a removable microSD card or USB OTG drive. Internal is faster and always present; external is optional and easy to swap out.AndroidmicroSD cardA microSD card is a removable flash-memory card that adds expandable storage to phones with a card slot. Many recent flagships have dropped the slot — Samsung’s Galaxy S line since the Galaxy S21, and every Google Pixel — so you cannot expand them.AndroidOBB filesOBB files are APK expansion files that hold the large assets — game graphics, audio, and levels — that do not fit inside an app’s install package. They live in Android/obb on internal storage and can be several gigabytes per game.AndroidScoped storageScoped storage is Android’s privacy model that limits which files an app can see. An app gets free access to its own private folder and to shared media it owns, but needs explicit permission to touch the rest of your files.AndroidSecure FolderSecure Folder is a Samsung feature that creates a separate, encrypted space on a Galaxy phone for private apps, photos, and files, locked behind its own PIN or biometrics. Its contents are stored on the device and count toward used storage.AndroidSmart StorageSmart Storage is an Android feature that automatically removes local copies of photos and videos already backed up to Google Photos once they have been on the device for a set period. The originals stay safe in the cloud while the device reclaims space.AndroidSystem storage (Android)On Android, System is the storage taken up by the operating system itself — the OS, preinstalled components, and core files. It appears in the storage breakdown as a slice users cannot delete, and it grows with OS updates.AndroidTrash / Recycle Bin (Android)Android has no single system-wide recycle bin; instead, individual apps keep their own. Google Photos holds deleted items in its Bin for about 60 days, and the Files by Google Trash holds them for about 30 days before erasing them.AndroidUSB OTGUSB OTG (On-The-Go) lets an Android phone act as a USB host, so it can read a flash drive, card reader, keyboard, or mouse plugged into its USB-C port. For storage, it is a quick way to offload photos and videos to an external drive without a computer.
Mac 9
macOS storage categories and disk-space concepts.
MacAPFS local snapshotAn APFS local snapshot is a point-in-time copy of your startup disk that Time Machine stores locally so you can restore recent changes even without the backup drive attached. The snapshots temporarily occupy disk space and macOS deletes them automatically when space is needed.MacDownloads folder (Mac)The Downloads folder is where Safari, Chrome, Mail, and Messages save files you receive on a Mac. It is one of the fastest-growing folders on most Macs because nothing removes installers, disk images, and attachments after you use them.MacPhotos library (Mac)The Photos library on a Mac is a single package file (Photos Library.photoslibrary) in your Pictures folder that holds all your images, videos, edits, and thumbnails. It is often the largest single item on a Mac.MacPurgeable spacePurgeable space is storage that macOS can reclaim automatically when the disk fills up — mainly caches, regenerable files, and cloud-stored content that has already been uploaded. It still appears used, but macOS frees it on demand rather than failing a write.MacSpotlight indexThe Spotlight index is the searchable database macOS builds of your files, apps, and their contents so search returns instant results. It uses some disk space and can be rebuilt, which temporarily raises CPU and disk activity.MacSystem Data (Mac)System Data on a Mac is the catch-all storage category for caches, logs, temporary files, fonts, virtual memory, and APFS local snapshots that do not fit Apps, Photos, or Documents. Much of it is reclaimable cache that macOS manages and purges on its own as space runs low.MacTime MachineTime Machine is macOS’s built-in backup feature. It copies your files, apps, and system to an external or network drive so you can restore them later, and keeps short-lived local snapshots on the startup disk between backups.MacTrash (Mac)The Trash on a Mac is a holding area for files you delete from Finder. The disk space they used is not reclaimed until you empty the Trash, so a full Trash can quietly keep gigabytes tied up.MacXcode Derived DataDerived Data is the folder where Xcode stores build products, indexes, and intermediate files for your projects. It can grow to tens of gigabytes and is safe to delete — Xcode rebuilds it on the next build.
Windows 15
Windows disk cleanup, caches, and system-file concepts.
WindowsAppData folder (Windows)AppData is a hidden per-user folder on Windows where installed programs store settings, profiles, and caches. It holds three subfolders — Roaming, Local, and LocalLow — and can grow large over time as app caches accumulate, though much of it is not safe to delete by hand.WindowsDelivery Optimization filesDelivery Optimization files are cached pieces of Windows updates and Store apps that your PC keeps to speed up installs and share with other devices on your network. The cache is safe to clear and Windows refills it only as needed.WindowsDirectX shader cacheThe DirectX Shader Cache is the Windows folder where the DirectX graphics system stores compiled shaders for games and apps. It is reclaimable junk: Windows Disk Cleanup lists it for removal, and DirectX rebuilds it automatically as you run programs again.WindowsDisk CleanupDisk Cleanup (cleanmgr.exe) is the built-in Windows utility that removes temporary files, caches, Recycle Bin contents, and old update files to free space on a drive. It is safe to run and only deletes data Windows considers expendable.WindowsHibernation file (hiberfil.sys)The hibernation file (hiberfil.sys) is a hidden Windows file that stores the contents of RAM when the PC hibernates, so it can resume exactly where you left off. It is typically several gigabytes and can be removed only by turning hibernation off.WindowsPagefile (pagefile.sys)The pagefile (pagefile.sys) is a hidden Windows system file used as virtual memory — overflow space on disk when physical RAM fills up. It is managed by Windows, often several gigabytes, and should not be deleted, since removing it can hurt stability and performance.WindowsRecycle BinThe Recycle Bin is a holding area on Windows that keeps deleted files so they can be restored. Until you empty it, those files still occupy disk space — deleting something does not free space until the bin is emptied or it fills its size limit.WindowsShader cacheA shader cache stores the compiled GPU programs (shaders) a game or app builds the first time it renders a scene, so they do not have to be recompiled on later runs. It is safe to clear: the cache rebuilds automatically, at the cost of brief stutter or a slower first launch afterward.WindowsStorage Sense (Windows)Storage Sense is a Windows 10/11 feature that automatically frees space by deleting temporary files, emptying the Recycle Bin, and clearing the Downloads folder on a schedule you set. It is the modern, automatic replacement for running Disk Cleanup by hand.WindowsSystem Restore pointA System Restore point is a saved snapshot of Windows system files, drivers, and Registry settings that lets you roll the PC back to an earlier working state without touching your personal files. The snapshots consume disk space, which System Protection caps and recycles as new ones are made.WindowsThumbnail cache (Windows)The Windows thumbnail cache stores small preview images of your photos, videos, and documents so File Explorer loads them quickly. It is safe to clear — Windows rebuilds the previews on demand the next time you open a folder.WindowsWindows RegistryThe Windows Registry is a central database of low-level settings for the operating system, hardware, and installed programs. It is critical to how Windows runs; editing it by hand carries real risk, and so-called “registry cleaners” free almost no disk space and can do harm.WindowsWindows temporary filesWindows temporary files are short-lived data that the system and apps create while running — installers, update caches, crash logs, and scratch files. Most are safe to delete; Windows recreates anything it still needs the next time it runs.WindowsWindows Update cleanupWindows Update cleanup removes the superseded files left behind after installing updates — old component versions kept for rollback. It can free several gigabytes and is done through Disk Cleanup or Storage Sense, not by deleting files by hand.WindowsWinSxS folderWinSxS (the component store) is the Windows folder that holds the files needed to install, update, and roll back system features. It looks huge because of shared hard links, but its real size is smaller — and you must never delete it manually.
Photos & video 72
Duplicates, capture modes, and the media that drives most storage use.
Photos & video10-bit color10-bit color records 1,024 levels per color channel instead of the 256 that 8-bit provides, giving over a billion possible colors. The extra levels produce smoother gradients with less banding, which is why HDR video uses 10-bit — at the cost of larger files.Photos & video4K video4K video is footage with roughly four times the pixels of 1080p HD, which makes it sharper but much larger — a minute of 4K can take up several hundred megabytes. On phones it is often the single biggest consumer of storage.Photos & videoAdaptive bitrate streaming (HLS)Adaptive bitrate streaming delivers video in short segments at multiple quality levels and switches between them on the fly to match your connection. HLS and MPEG-DASH are the common protocols — they are why streams scale resolution up or down to avoid buffering.Photos & videoApple ProRAWApple ProRAW is a RAW photo format on supported iPhone Pro models that keeps far more of the camera’s original image data for editing. The trade-off is size: a single ProRAW shot is many times larger than a normal HEIC or JPEG photo.Photos & videoAspect ratioAspect ratio is the proportional relationship between an image or video’s width and height, written as two numbers like 4:3 or 16:9. It shapes how a photo fills the frame and has a smaller effect on file size than resolution or quality.Photos & videoAV1 vs HEVCAV1 and HEVC (H.265) are next-gen video codecs that store the same quality in less space than H.264. AV1 is royalty-free and slightly more efficient; HEVC has broader hardware support, especially on Apple devices, but carries licensing costs.Photos & videoBit depthBit depth is the number of bits used to record each color channel, which sets how many distinct tones an image or video can hold. Higher bit depth (10-bit vs 8-bit) means smoother gradients and more editing headroom, but it also makes files larger.Photos & videoBitrate mode (CBR vs VBR)Bitrate mode controls how an encoder spends data over time. Constant bitrate (CBR) holds a steady data rate throughout, while variable bitrate (VBR) spends more on complex scenes and less on simple ones — usually giving better quality per megabyte for a similar file size.Photos & videoBitrate vs ResolutionResolution is how many pixels a video frame contains, while bitrate is how many bits are stored per second of playback. File size is driven by bitrate and duration, not resolution alone, so a high-resolution clip recorded at a low bitrate can be smaller than a lower-resolution clip at a high bitrate.Photos & videoBurst Photo StorageBurst mode captures many full-resolution photos in a single press, so one burst can leave a dozen or more near-identical files on the device. Each frame is a complete image at normal size, which means bursts quietly multiply camera-roll storage with redundant shots you rarely revisit.Photos & videoBurst photosA burst is a rapid series of photos captured in one press, designed to catch fast action so you can pick the sharpest frame. Each burst can hold dozens of nearly identical images, so leaving every frame stored is a common source of wasted space.Photos & videoChroma subsampling (4:2:0)Chroma subsampling saves space by storing full brightness detail but fewer color samples, exploiting the fact that human eyes notice brightness more than color. Notations like 4:2:0, 4:2:2, and 4:4:4 describe how much color information is kept — 4:2:0 keeps the least and is the most common.Photos & videoChroma Subsampling 4:2:0 vs 4:4:4Chroma subsampling stores full brightness (luma) but fewer color (chroma) samples to shrink files. **4:4:4** keeps every color sample; **4:2:0** keeps a quarter of them, roughly halving raw data with little visible loss because eyes are far less sensitive to color detail than brightness.Photos & videoColor bandingColor banding is the visible steps or stripes that appear in what should be a smooth gradient — often across skies, shadows, or sunsets. It happens when an image has too few tonal levels to render the transition smoothly, typically from low bit depth or heavy compression.Photos & videoColor gamutColor gamut is the range of colors a device, format, or color space can capture, store, or display. A wider gamut covers more saturated and vivid colors; a narrower one clips them to its nearest available shades.Photos & videoColor gradingColor grading is the process of adjusting a video’s color, contrast, and tone to set a look and mood. It builds on color correction, which first fixes exposure and white balance, and is often applied using LUTs (lookup tables) for a consistent style across clips.Photos & videoColor Profile (ICC)An ICC color profile is metadata that tells software how to interpret an image's raw color values, mapping them to a defined color space such as **sRGB**, **Display P3**, or **Adobe RGB** so colors look consistent across screens. It can be embedded in the file or referenced by a small tag.Photos & videoConstant Rate Factor (CRF)Constant Rate Factor (CRF) is a quality-based encoding mode in **x264**, **x265**, and similar encoders. You set a single quality number and the encoder varies the bitrate to hold that quality, letting the final file size float instead of targeting it directly.Photos & videoContainer vs CodecA container (like MP4 or MOV) is the file wrapper that holds and synchronizes streams, while a codec (like H.264 or HEVC) is the algorithm that actually encodes the video and audio inside it. The file extension names the container, not the codec.Photos & videoDCI-P3DCI-P3 is a wide color gamut originally defined for digital cinema and now common on phones, tablets, and laptops. It covers noticeably more saturated greens and reds than sRGB, so P3 content looks more vivid on a display that supports it.Photos & videoDuplicate photosDuplicate photos are exact or near-exact copies of the same image — created by saving a photo twice, importing from multiple sources, or editing and re-saving. They are low-risk to remove because an identical copy remains.Photos & videoEntropy CodingEntropy coding is the final, lossless stage of compression that assigns shorter bit patterns to common symbols and longer ones to rare symbols, squeezing out statistical redundancy. Huffman and arithmetic coding are the classic methods used in JPEG, PNG, ZIP, and video codecs.Photos & videoEXIF InternalsEXIF is metadata embedded inside JPEG and HEIF photos using a TIFF-style structure of IFDs and tags. It records camera settings, timestamps, and often GPS coordinates, adding bloat and personally identifying information to every shot.Photos & videoEXIF metadataEXIF metadata is the information embedded inside a photo file describing how and where it was taken — camera model, exposure settings, date, time, and often GPS location. It is tiny in size but matters for privacy and for how photos are sorted and searched.Photos & videoFrame rate (fps)Frame rate is how many still images a video shows each second, measured in frames per second (fps). Higher frame rates make motion smoother but record more data, so a 60 fps clip uses more storage than the same clip at 30 fps.Photos & videoGain Map (HDR Photos)A gain map is an extra grayscale layer stored inside an HDR photo that tells a display how much to brighten each pixel beyond the standard image. It lets one file look normal on SDR screens and brighter on HDR screens, at the cost of added file size.Photos & videoGeotaggingGeotagging embeds the GPS coordinates where a photo or video was taken into the file’s metadata. It powers map and place features but is also a privacy consideration, since the location travels with the file when you share it.Photos & videoHDR photoAn HDR (high dynamic range) photo blends several exposures to keep detail in both bright and dark areas of a scene. Because the camera may save extra data or multiple frames, HDR images can be somewhat larger than a single standard shot.Photos & videoHEICHEIC is the file format iPhones use to save photos by default. It stores the same image quality as JPEG in roughly half the space using HEIF compression, which is why switching away from it makes your library larger.Photos & videoHEIC vs JPEG SizeHEIC, Apple's container for HEVC-encoded images, typically stores a photo at roughly half the file size of an equivalent-quality JPEG. It achieves this with a newer, more efficient compression algorithm. On iPhones using HEIC instead of JPEG meaningfully shrinks how much space the camera roll consumes.Photos & videoHEVC vs H.264H.264 (AVC) and HEVC (H.265) are video compression standards. HEVC is the newer one and typically reaches the same visual quality at roughly half the bitrate of H.264, so HEVC photos and videos take noticeably less storage at equal quality. The tradeoff is heavier processing and narrower compatibility.Photos & videoImage DownsamplingImage downsampling reduces a photo's pixel dimensions, computing fewer output pixels from many input pixels. Because file size scales with pixel count, halving width and height cuts the pixel total to roughly a quarter, which is how compressors shrink photos for storage.Photos & videoImage PyramidAn image pyramid is a set of progressively smaller copies of the same image, each at half the resolution of the one below. Apps pick the level closest to the size they need, which speeds up rendering and is the idea behind mipmaps and gallery thumbnails.Photos & videoImage resolutionImage resolution is the pixel dimensions of a photo — its width by height, such as 4032 × 3024. Higher resolution holds more detail but takes more storage, so larger images make a photo library grow faster.Photos & videoInterframe compressionInterframe compression shrinks video by storing only what changes between frames instead of a full picture each time. After a keyframe, later frames (P-frames and B-frames) record motion and differences, which is how video files stay far smaller than a folder of separate images.Photos & videoInterlacing vs progressiveInterlaced video draws each frame as two alternating fields of odd and even lines, while progressive video draws every line in order as a full frame. The "i" and "p" in formats like 1080i and 1080p mark the difference — modern screens and files are almost all progressive.Photos & videoIntra vs Inter FrameIntra (I) frames are coded as standalone images, like a JPEG. Inter (P/B) frames store only the changes from nearby frames, so they are far smaller. This temporal redundancy is why video files shrink dramatically compared to storing each frame as a photo.Photos & videoIPTC MetadataIPTC metadata is a standard for embedding descriptive text inside image files - captions, keywords, creator, copyright, and location - so the information travels with the photo. It is stored alongside EXIF and XMP in JPEG, TIFF, and HEIC files.Photos & videoJPEG Quality FactorThe JPEG quality factor is a 1-100 setting that controls how aggressively a photo's color and detail data is quantized during compression. Higher values keep more detail and a larger file; lower values shrink the file by discarding visual information.Photos & videoKeyframe (I-frame)A keyframe, or I-frame, is a fully self-contained video frame that holds a complete picture without referencing any other frame. Keyframes anchor compression and seeking, but because they store the whole image they are the largest frames in a video.Photos & videoLetterboxing & pillarboxingLetterboxing adds black bars above and below a video, and pillarboxing adds them to the left and right, so footage of one aspect ratio fits a screen of another without stretching or cropping. The bars preserve the original framing; they are not part of the picture.Photos & videoLive PhotoA Live Photo is an iPhone still image bundled with a short ~3-second video and audio clip captured around the moment you press the shutter. Because it stores both a full-resolution photo and a small movie, a Live Photo takes up roughly twice the space of an ordinary still.Photos & videoLive Photo Storage AnatomyA Live Photo is stored as two paired files: a full-resolution still (HEIC or JPEG) plus a short Motion video (a few seconds of QuickTime .mov). That bundled video is why a Live Photo takes roughly twice the space of a normal photo.Photos & videoLossy vs Lossless CompressionLossy compression permanently discards image or video data the eye is least likely to notice, shrinking files dramatically. Lossless compression repacks data so the original is perfectly reconstructable, saving far less space. Camera-roll formats like JPEG, HEIC, and H.264 are lossy, which is why deleting them, not re-compressing them, frees the most storage.Photos & videoMegapixelA megapixel is one million pixels, and it describes how many pixels make up a photo. More megapixels capture more detail but produce larger files, so a higher-MP camera fills your storage faster for the same number of shots.Photos & videoMotion CompensationMotion compensation is a video compression technique that encodes a frame as motion vectors pointing to similar blocks in earlier or later frames, plus a small residual, instead of storing every pixel again. It is the main reason video files are far smaller than the sum of their frames.Photos & videoNoise reductionNoise reduction is processing that smooths out the random speckles and grain that appear in photos and videos shot in low light or at high ISO. It trades fine detail for a cleaner image, so heavy noise reduction can leave skin and textures looking soft or waxy.Photos & videoPanoramaA panorama is a single wide photo built by sweeping the camera across a scene and stitching the frames together. The result is a very high-resolution, elongated image that takes more storage than an ordinary photo.Photos & videoPhoto Cache vs Photo StoragePhoto storage is your real, permanent photo files (the originals saved in your camera roll or gallery). Photo cache is temporary data apps generate from those photos, such as thumbnails, previews, and downloaded copies, to load images faster. Clearing photo cache never deletes your real photos; it only removes regenerable scratch data.Photos & videoProgressive vs Baseline JPEGBaseline JPEG encodes an image top to bottom, so it renders line by line as it downloads. Progressive JPEG stores the same image in multiple passes, showing a full but blurry frame first that sharpens with each pass - often at a slightly smaller file size.Photos & videoProRAW File SizeApple ProRAW saves a high-bit-depth DNG that keeps far more image data than a HEIC, so a single ProRAW shot is many times larger than a normal photo. This is why ProRAW capture fills iPhone storage quickly.Photos & videoQuantization (Compression)Quantization is the lossy step in image and video compression that rounds away fine detail the eye barely notices. Coarser quantization throws out more data and produces smaller files, which is why a lower quality setting yields a smaller photo.Photos & videoRAW vs JPEG StorageA RAW file records the camera sensor's unprocessed data with little or no lossy compression, so it is many times larger than the JPEG or HEIC the phone would otherwise save. RAW gives maximum editing flexibility at a steep storage cost, which is why shooting RAW fills a camera roll far faster.Photos & videoRemuxingRemuxing rewraps a video's existing audio and video streams into a different container format (for example MKV to MP4) without re-encoding them. It changes the file's container, not its pixels, so it is fast and lossless.Photos & videoRolling shutterRolling shutter is a distortion that appears when a camera sensor captures an image line by line instead of all at once. Fast motion can look skewed, wobbly, or smeared because different parts of the frame are recorded at slightly different moments.Photos & videoScreen recordingA screen recording is a video that captures everything happening on your display, saved to your photo library. These clips are easy to make and often forgotten, so they quietly pile up and consume storage like any other video.Photos & videoScreenshotA screenshot is an image captured of whatever is on your screen, saved into your photo library like a regular picture. Individually small, screenshots accumulate fast and clutter the camera roll because most are saved once and never needed again.Photos & videoScreenshot Storage CostScreenshots are saved as full-resolution PNG or HEIC images in your camera roll, so they accumulate alongside real photos. Individually small, they pile up by the hundreds and quietly consume photo-library storage.Photos & videoSimilar photosSimilar photos are different frames of the same moment — retakes, bursts, and small variations of one shot — rather than exact copies. They quietly pile up because we shoot several versions to get one good frame, and the rest stay in the library.Photos & videoSlow-motion videoSlow-motion video records at a very high frame rate — often 120 or 240 fps — so it can be played back slowly while staying smooth. Capturing so many frames per second makes slo-mo clips large for their length.Photos & videoThumbnail GenerationThumbnail generation is the process of decoding a photo or video frame, downscaling it to a small preview, and saving that preview so galleries can scroll smoothly without re-reading full-resolution originals. The cached previews are extra files that accumulate and consume storage over time.Photos & videoThumbnail StrippingThumbnail stripping removes the small preview image many cameras embed inside a photo's metadata. The embedded thumbnail speeds up previews but can survive edits and leak the original, uncropped frame, so privacy tools strip it.Photos & videoTime-lapseTime-lapse captures frames at long intervals and plays them back quickly, compressing minutes or hours into a short clip. Because it keeps only selected frames, a finished time-lapse is usually compact for the span of time it covers.Photos & videoTranscodingTranscoding is decoding a video and re-encoding it into a different codec, bitrate, resolution, or container. It is how a compressor shrinks a file or makes it playable on another device — and because re-encoding is lossy, each pass can lower quality slightly.Photos & videoTwo-Pass EncodingTwo-pass encoding compresses video in two stages: a first pass analyzes the whole clip's complexity, and a second pass uses that data to distribute bitrate intelligently. It hits a target file size more accurately than single-pass encoding.Photos & videoVariable Bitrate (VBR)Variable bitrate (VBR) encoding spends more data on complex, fast-moving scenes and less on simple, static ones, instead of a fixed rate. This improves quality per byte and is why two videos of the same length and resolution can have very different file sizes.Photos & videoVideo stabilizationVideo stabilization smooths out camera shake to make footage look steady. Optical stabilization (OIS) physically counters motion in the lens or sensor, while electronic stabilization (EIS) corrects it in software by cropping and shifting each frame.Photos & videoVideo Thumbnail CacheA video thumbnail cache is the set of small preview frames a gallery or photos app generates and stores so a video library scrolls instantly instead of decoding each clip on demand. The thumbnails are derived, so deleting them only forces regeneration, not data loss.Photos & videoVignettingVignetting is the darkening of an image toward its corners and edges compared with the center. It is usually a lens effect — less light reaches the edges of the frame — though it is also added deliberately in editing to draw the eye toward the subject.Photos & videoVP9VP9 is a royalty-free video codec developed by Google, typically carried in WebM or MP4 containers. It compresses roughly as efficiently as HEVC and powers much of YouTube's higher-resolution streaming, producing smaller files than the older H.264 at the same quality.Photos & videoWhite balanceWhite balance is the camera setting that adjusts colors so white objects look white under different lighting. It corrects the color temperature of a scene — warm orange indoor light or cool blue shade — so photos and videos look natural instead of tinted.Photos & videoXMP MetadataXMP (Extensible Metadata Platform) is an Adobe-created, XML-based standard for embedding metadata such as edits, ratings, keywords, and copyright into images, PDFs, and video, either inside the file or in a separate .xmp sidecar file. It adds a small amount to file size.
Files & formats 277
Image, video, audio, and document formats and what they cost in space.
Files & formats.conf / .cfgA .conf or .cfg file is a plain-text configuration file holding the settings a program reads to control its behavior. There is no single standard — each app defines its own syntax — but most are human-readable key/value or sectioned text.Files & formats.gitignoreA .gitignore is a plain-text file that tells the Git version-control system which files and folders to leave untracked — typically secrets, build output, caches, and large generated files that should not be saved into a project’s history.Files & formats.propertiesA .properties file is a plain-text configuration format, most associated with Java, that stores settings as simple key=value pairs. Each line sets one property, making it an easy, human-readable way to configure an application.Files & formats3DS (3D Studio)3DS is an old 3D model format from Autodesk’s original 3D Studio for DOS. It stores meshes, basic materials, and simple animation, and it survives as a widely supported exchange format despite its age and limits.Files & formats3GP3GP is a compact video container created for early 3G mobile phones, designed to keep file sizes and bandwidth low. It is largely outdated now, so 3GP files are usually old clips recorded on or sent from older phones.Files & formats7Z (7-Zip)7z is an open archive format from the free 7-Zip tool, known for a very high compression ratio thanks to LZMA/LZMA2. It typically packs tighter than ZIP, but the recipient needs a 7z-capable app to open it.Files & formatsAAB (Android App Bundle)An AAB (Android App Bundle) is the publishing format developers upload to Google Play. Play uses it to generate and deliver device-specific APKs, so each phone downloads only the code and resources it needs rather than one large universal package.Files & formatsAACAAC (Advanced Audio Coding) is a lossy audio format designed as the successor to MP3, delivering better sound at the same file size. It is the default for Apple Music, iTunes, and YouTube, and is what iPhones use for recorded audio.Files & formatsABC (Alembic)ABC (Alembic) is an open 3D format for exchanging baked, animated geometry between apps. Instead of rigs and controls, it stores the final per-frame shape of a scene, making it a reliable hand-off format in VFX and animation.Files & formatsAC-3 (Dolby Digital)AC-3, better known as Dolby Digital, is a lossy audio format built for surround sound in movies, DVDs, and TV. It can carry up to 5.1 channels — five speakers plus a subwoofer — in a compressed stream small enough to fit alongside video. It is lossy, so some original detail is discarded.Files & formatsACCDB (Access)ACCDB is the database file format Microsoft Access has used since Access 2007. A single .accdb holds an entire desktop database — tables, queries, forms, and reports — replacing the older MDB format.Files & formatsACEACE is a proprietary compressed archive format, created with WinAce, that once offered high compression ratios. It is now obsolete and has been flagged for serious security vulnerabilities, so opening .ace files is discouraged.Files & formatsAI (Adobe Illustrator)AI is Adobe Illustrator’s native vector format for logos, icons, and illustrations. It stores artwork as editable paths and layers rather than pixels, so it scales to any size without quality loss. File size depends on complexity, not output resolution.Files & formatsAIFC (compressed AIFF)AIFC (AIFF-C, .aifc) is a compressed variant of Apple’s AIFF audio format. Where standard AIFF stores uncompressed audio, AIFC adds support for compression codecs inside the same container, so files can be smaller — though depending on the codec, it may be lossy.Files & formatsAIFFAIFF (Audio Interchange File Format) stores uncompressed audio, the Apple counterpart to Windows WAV. It holds the raw, full-quality recording with no compression, so files are large — roughly ten times the size of an MP3 for the same length of audio.Files & formatsALAC (Apple Lossless)ALAC (Apple Lossless Audio Codec) compresses audio with no loss of quality — it reproduces the original recording exactly while taking up less space than uncompressed PCM. Because nothing is discarded, ALAC files are much larger than lossy MP3 or AAC, typically several times the size.Files & formatsAlpha channel (transparency)An alpha channel is the part of an image that records transparency — how see-through each pixel is. It lets formats like PNG, WebP, and GIF place a subject over any background. JPEG has no alpha channel, so it cannot store transparency.Files & formatsAMRAMR (Adaptive Multi-Rate) is a lossy audio format optimized for speech, used by older phones for voice recordings, voicemail, and MMS. It compresses voice very aggressively, so files are extremely small — but it sounds poor for music because it is tuned only for the human voice.Files & formatsAnimated WebPAnimated WebP stores a short animation in a single WebP file, supporting full color, alpha transparency, and both lossy and lossless compression. It typically produces much smaller files than an equivalent GIF or APNG at similar quality.Files & formatsAPE (Monkey’s Audio)APE (Monkey’s Audio) is a lossless audio format that compresses CD-quality sound with no loss in quality, typically smaller than the original WAV. It plays back identical to the source, but native support is rare outside dedicated audio players, so it is often converted to FLAC or MP3 for everyday use.Files & formatsAPK (Android app package)An APK is the package format Android uses to distribute and install apps. It is a ZIP archive that bundles the app’s compiled code, resources, and a manifest. Leftover APK installers in your Downloads folder are safe to delete once the app is installed.Files & formatsAPNGAPNG (Animated PNG) is an extension of the PNG format that stores a short animation in a single file with full lossless color and alpha transparency. It looks sharper than GIF — especially for gradients and translucency — but the files are usually larger.Files & formatsArchive fileAn archive file bundles many files and folders into one container — for example a ZIP, RAR, or 7z. Most archives also compress their contents to save space, but some (like plain TAR) only bundle without shrinking anything.Files & formatsARJARJ is a DOS-era compressed archive format that bundles and shrinks files, like ZIP. It was known for strong compression and multi-volume archives that could span several floppy disks, but is now largely obsolete.Files & formatsARW (Sony RAW)ARW (Sony Alpha Raw) is Sony’s RAW image format, holding the unprocessed sensor data from Sony Alpha and Cyber-shot cameras. Files are large (often 20–60 MB) and need Sony’s software, Lightroom/Adobe Camera Raw, or conversion to DNG or JPEG to edit and share.Files & formatsASS / SSA subtitlesASS (Advanced SubStation Alpha) and its predecessor SSA are subtitle formats that add styling on top of plain text — fonts, colors, positioning, and on-screen effects. Unlike a basic SRT, an .ass file can place and animate captions anywhere on screen, which is why fansubs and anime use it.Files & formatsAU / SND (Sun audio)AU (.au, also .snd) is a legacy audio format from Sun Microsystems and NeXT, common on early Unix systems and the old web. It is a simple container, often holding basic PCM or μ-law audio, and is now obsolete — files are typically converted to MP3 or WAV for modern playback.Files & formatsAVIAVI (Audio Video Interleave) is a legacy Microsoft video container from the 1990s. It can hold many different codecs, but it lacks modern features and tends to produce larger files than MP4, so it is mostly seen in older video.Files & formatsAVIFAVIF (.avif) is a next-generation image format based on the AV1 video codec. It typically produces smaller files than JPEG or WebP at the same quality and supports transparency, HDR, and wide color — making it one of the most space-efficient formats available.Files & formatsAvroAvro is an open row-based data serialization format from the Apache ecosystem. It stores records together with their schema, making it compact and self-describing, and is common in data pipelines and streaming such as Kafka.Files & formatsAZW3 (Kindle)AZW3, also called Kindle Format 8 (KF8), is Amazon’s ebook format that succeeded MOBI on Kindle devices. It supports richer formatting and layout than MOBI and may carry Amazon DRM that ties a book to your Kindle account.Files & formatsBAK (backup) fileA BAK file (.bak) is a backup copy of another file, created automatically by an app before it saves or changes the original. It exists as a safety net, and once you are sure the current version is fine, the .bak is usually safe to delete.Files & formatsBDF (bitmap font)BDF (Glyph Bitmap Distribution Format) is a text-based bitmap font format from the X Window System. Each character is described as a grid of pixels in plain text, making it readable, editable, and easy to convert.Files & formatsBIN file (.bin)A BIN file (.bin) is a generic binary file — data stored in raw machine-readable form rather than plain text. The label only says "not text," so a .bin could be firmware, a disk image, app data, or part of a larger package, depending on its source.Files & formatsBIN/CUEBIN/CUE is a two-file optical-disc image: the .bin holds the raw sector-by-sector data of a CD or DVD, and the small .cue is a text sheet describing the disc layout — tracks, types, and where each begins. Together they let software mount or burn an exact copy of the original disc.Files & formatsBLEND (Blender)BLEND is the native project file of Blender, the free 3D software. It saves an entire scene — models, materials, textures, lights, cameras, animation, and even editor layout — in one binary file, so it is a working document rather than an interchange format.Files & formatsBMPBMP (.bmp), or bitmap, is an old Windows image format that usually stores pixels with little or no compression. The result is very large files — often many times the size of the same image as JPEG or PNG — so it is rarely a good way to keep photos.Files & formatsBrotli (.br)Brotli is a lossless compression algorithm developed by Google, used widely to compress web pages, fonts, and assets. It typically achieves smaller sizes than gzip for text, which is why browsers and servers support it for faster page loads.Files & formatsBZIP2 (.bz2)BZIP2 is a single-file compressor that produces .bz2 files. It generally achieves a higher compression ratio than gzip but is noticeably slower, and like gzip it pairs with TAR to compress whole folders as tar.bz2.Files & formatsC4D (Cinema 4D)C4D is the native project format of Maxon Cinema 4D, a 3D modeling, motion-graphics, and animation app. A .c4d file holds the full scene — geometry, materials, lights, cameras, and animation — and is meant to be opened in Cinema 4D.Files & formatsCAB (Windows cabinet)A CAB (cabinet) is a compressed archive format Microsoft uses to package Windows installers, drivers, and update components. Windows opens .cab files natively in File Explorer, and tools like 7-Zip can extract them too.Files & formatsCAF (Core Audio Format)CAF (Core Audio Format) is Apple’s flexible audio container, used across macOS and iOS. Like MKA, it is a wrapper rather than a codec and can hold many audio types. Unlike older formats such as WAV and AIFF, it is not limited to 4 GB, so it suits very long or high-resolution recordings.Files & formatsCamera RAW (CR2, NEF, ARW)Camera RAW is the umbrella for manufacturer-specific files that store unprocessed data straight off the camera sensor — Canon CR2/CR3, Nikon NEF, Sony ARW, and others. They keep maximum editing flexibility, which makes them far larger than the JPEG or HEIC the same shot would produce.Files & formatsCBRCBR is a comic-book file format that is a RAR archive of image files — one image per page — renamed with a .cbr extension. Comic readers open it, sort the pages by filename, and display them in order.Files & formatsCBT (comic TAR)CBT is a comic-book archive that is simply a TAR file of page images renamed with a .cbt extension. Comic readers open it, sort pages by filename, and display them in order — the same idea as CBZ but using TAR instead of ZIP.Files & formatsCBZCBZ is a comic-book file format that is simply a ZIP archive of image files — one image per page — renamed with a .cbz extension. Comic readers open it, sort the pages by filename, and display them in order.Files & formatsCDR (CorelDRAW)CDR is CorelDRAW’s native vector format for logos, layouts, and print artwork, common in sign-making and apparel design. Like other vector formats it stores editable paths rather than pixels, so it scales without quality loss but opens reliably only in Corel software.Files & formatsCodecA codec is the method used to compress and decompress video or audio — it decides how much detail is kept and how small the file becomes. Common video codecs are H.264 and HEVC (H.265); common audio codecs are AAC and MP3. The codec, not the file extension, controls quality and size.Files & formatsColor space (sRGB, CMYK)A color space defines the range of colors an image can use and how they map to red, green, blue, or print inks. sRGB is the standard for screens and the web; CMYK is for print. Using the wrong one makes colors look dull or shifted.Files & formatsContainer formatA container format is the file wrapper that packages compressed video, audio, subtitles, and metadata into one file — for example MP4, MOV, or MKV. It defines how the parts are stored together, not how they are compressed; the codec inside does that.Files & formatsCPIOCPIO ("copy in, copy out") is a Unix archive format that bundles many files into one stream, similar to tar. It is used in software packaging (inside RPM packages) and in Linux initial-RAM-disk (initramfs) images.Files & formatsCR2 (Canon RAW)CR2 is Canon’s older RAW image format, holding the unprocessed sensor data from many Canon DSLR and mirrorless cameras. Files are large (often 20–40 MB each) and need Canon’s software, Lightroom/Adobe Camera Raw, or conversion to DNG or JPEG to edit and share.Files & formatsCR3 (Canon RAW)CR3 is Canon’s current RAW image format, used on newer Canon cameras in place of CR2. It stores unprocessed sensor data with better compression, but files stay large (often 20–40 MB) and need recent Canon software, Lightroom/Camera Raw, or conversion to DNG or JPEG.Files & formatsCSSCSS (Cascading Style Sheets) is the text-based language that controls how web pages look — colors, fonts, spacing, and layout. It separates a page’s visual design from its HTML structure.Files & formatsCSVCSV (comma-separated values) is a plain-text format that stores tabular data as rows of values separated by commas. It carries no formatting, formulas, or charts, which makes CSV files tiny and universally readable across apps and programming languages.Files & formatsDAE (COLLADA)DAE is the file extension for COLLADA, an open XML-based 3D interchange format. It can store geometry, materials, textures, and animation as readable text, and it was a common bridge between 3D tools before glTF became the modern web standard.Files & formatsDAT file (.dat)A DAT file (.dat) is a generic data file with no single fixed format — its meaning depends entirely on the app that created it. A .dat might hold app data, saved game state, mail attachments, or configuration, so what to do with one depends on its source.Files & formatsDBF (dBASE)DBF is a simple database table format that originated with dBASE and the xBase family of databases. Each .dbf holds one table of records, and the format is still common in legacy systems, FoxPro data, and GIS shapefile attributes.Files & formatsDDS (DirectDraw Surface)DDS (DirectDraw Surface) is a Microsoft image format built for game and 3D textures. It can store GPU-ready compressed textures with mipmaps, so graphics hardware loads them directly without re-encoding.Files & formatsDEB (Debian package)A DEB is the software package format used by Debian, Ubuntu, and related Linux distributions. It is an archive holding a program’s files plus install scripts and metadata, installed through a package manager like apt or dpkg.Files & formatsdfont (Mac font)A dfont is a Mac font format that stores font data in a file’s data fork instead of the classic resource fork. Apple used it in early macOS to keep traditional Mac fonts working as single, portable files.Files & formatsDigital signatureA digital signature on a PDF marks who signed a document and confirms it has not been altered since. It ranges from a simple drawn or typed signature image to a cryptographic signature backed by a certificate that can be mathematically verified.Files & formatsDisk imageA disk image is a single file that mirrors the entire contents of a disk or volume — its file system, structure, and data. Common types include ISO (discs), DMG (macOS), and IMG. You mount or write a disk image rather than just extracting files from it.Files & formatsDivXDivX is an MPEG-4 Part 2 video codec that became hugely popular in the early 2000s for shrinking DVD-quality movies to a fraction of their size, often small enough to fit on a CD. It is a codec (and brand), not a container, and is largely superseded by H.264.Files & formatsDjVuDjVu is a file format built for storing scanned documents — books, manuscripts, and archives — at small sizes. It separates page text from background images so high-resolution scans compress far smaller than the equivalent PDF.Files & formatsDMG (Apple disk image)A DMG is Apple’s disk-image format, used mainly to distribute Mac apps. You double-click it to mount a virtual drive, drag the app to Applications, then eject and delete the .dmg — you do not "install" the DMG itself.Files & formatsDNG (digital negative)DNG (Digital Negative) is an open raw image format created by Adobe. Like other raw files, it stores the unprocessed sensor data from a camera for maximum editing flexibility — and like all raw files, it takes far more storage than a JPEG or HEIC.Files & formatsDockerfileA Dockerfile is a plain-text script of step-by-step instructions that Docker follows to build a container image — a packaged, runnable copy of an app with its operating system, libraries, and dependencies included.Files & formatsDOCX (Word)DOCX is the default file format for Microsoft Word documents since Word 2007. It is a ZIP package of compressed XML, so a text-heavy document stays small — but embedded photos and fonts are what actually inflate the file size.Files & formatsDRC (Draco 3D)DRC is the file format of Draco, an open-source library from Google for compressing 3D meshes and point clouds. It shrinks geometry dramatically so 3D models download and load faster, especially on the web.Files & formatsDSDDSD (Direct Stream Digital) is a high-resolution audio format used for SACDs and audiophile downloads. It captures sound a different way than standard PCM and aims for extreme fidelity, but files are very large and need compatible hardware or software, so it is a niche format.Files & formatsDTS (Digital Theater Systems)DTS (Digital Theater Systems) is a family of surround-sound audio codecs used in cinemas, Blu-ray, and home theater, competing with Dolby formats. It carries multichannel audio (such as 5.1 or 7.1) and is usually a lossy codec, though some DTS variants are lossless.Files & formatsDV (Digital Video)DV (Digital Video) is the standard-definition format and codec used by consumer and prosumer camcorders, especially MiniDV tapes, from the late 1990s onward. It uses light intraframe compression, so files are large for their resolution and benefit from conversion to modern codecs.Files & formatsDVIDVI (Device Independent) is the original page-layout output format produced by the TeX typesetting system. It describes where text and rules go on each page without embedding fonts, and is usually converted onward to PostScript or PDF.Files & formatsDWG (AutoCAD drawing)DWG is the native binary format for AutoCAD drawings. It stores precise 2D and 3D CAD geometry plus layers, blocks, dimensions, and metadata. Because it is proprietary to Autodesk, opening it outside AutoCAD relies on compatible apps or DWG viewers.Files & formatsDXF (CAD exchange)DXF is an open, documented CAD exchange format created by Autodesk so drawings can move between different programs. It stores the same kind of vector geometry as DWG — lines, arcs, layers, text — but in a published format, usually as readable text.Files & formatsENV (.env) fileA .env (dotenv) file is a plain-text file that stores configuration as KEY=value lines, typically secrets like API keys, passwords, and database URLs that an app reads at startup. Because it holds credentials, it should never be committed to a public repository.Files & formatsEOT (Embedded OpenType font)EOT (Embedded OpenType) is a legacy web-font format Microsoft created for older versions of Internet Explorer. It packages an OpenType/TrueType font for use on web pages, but it is obsolete today and has been replaced by WOFF and WOFF2.Files & formatsEPSEPS (Encapsulated PostScript) is a vector graphics format used mainly for logos, illustrations, and print artwork. Like other vector files, it stores shapes as math rather than pixels, so it scales to any size — though it is an older format now often replaced by SVG and PDF.Files & formatsEPUBEPUB is the open standard format for ebooks. It is a ZIP package of HTML, CSS, and images, and its text reflows to fit any screen size — unlike a PDF, which keeps a fixed page layout. Most e-readers except Amazon Kindle support it natively.Files & formatsESD (Windows image)ESD (Electronic Software Download) is a heavily compressed, encrypted variant of the Windows WIM image format. Microsoft uses it to deliver Windows installations and updates over the internet, since it is smaller than an equivalent WIM.Files & formatsEXR (OpenEXR)EXR (OpenEXR) is a high-dynamic-range image format from Industrial Light & Magic, used in visual effects and rendering. It stores floating-point color with deep precision and multiple layers, so files are large but preserve detail far beyond standard 8-bit images.Files & formatsF4V (Flash MP4)F4V is an Adobe Flash video container based on the standard MP4/ISO file format, introduced to carry H.264 video for the Flash Player. With Flash discontinued at the end of 2020, F4V is a legacy format usually converted to plain MP4 today.Files & formatsFaviconA favicon is the small icon a browser shows next to a site’s name in tabs, bookmarks, and history. It is usually a tiny square image (commonly an ICO, PNG, or SVG) and is one of the smallest files a website serves.Files & formatsFB2FB2 (FictionBook) is an XML-based ebook format that stores a whole book — text, structure, and metadata — in a single file. It is popular in Eastern European ebook communities and reflows text to fit any screen, similar in purpose to EPUB.Files & formatsFBX (3D)FBX is a rich 3D interchange format owned by Autodesk that can carry geometry, materials, textures, rigs, and animation in a single file. It is the common pipeline format for games and film, and files tend to be large because they bundle so much.Files & formatsFillable PDF formA fillable PDF form is a PDF with interactive fields — text boxes, checkboxes, dropdowns, and signature areas — that you can type into and save directly, without printing. The form layout stays fixed while the field values are stored as editable data.Files & formatsFLACFLAC (Free Lossless Audio Codec) is a lossless audio format that compresses music with no loss of quality — the decoded file is bit-for-bit identical to the original. That fidelity comes at a cost: FLAC files are several times larger than MP3 or AAC.Files & formatsFLV (Flash video)FLV is the Flash Video container that dominated web video in the 2000s, used by early YouTube and many streaming sites. With Adobe Flash discontinued at the end of 2020, FLV is now a deprecated, legacy format.Files & formatsFON (bitmap font)FON is an old Windows font format that stores fonts as bitmaps — fixed-pixel images of each character — rather than scalable outlines. It was used for system fonts in early Windows and only renders well at its built-in sizes.Files & formatsGeoJSONGeoJSON is a JSON-based format for representing geographic features — points, lines, and polygons — along with their properties. It is the common, web-friendly way to store and exchange map data in browsers and mapping tools.Files & formatsGIFGIF (.gif) is an old image format best known for short looping animations. It is limited to 256 colors and uses inefficient compression, so an animated GIF is often far larger than the same clip saved as an MP4 video.Files & formatsGIFVGIFV is not a real file format — it is a label Imgur coined for looping clips that look like GIFs but are actually delivered as MP4 or WebM video. The trick gives GIF-style autoplay loops at a fraction of a true GIF’s file size.Files & formatsglTF / GLB (3D)glTF is an open, royalty-free 3D format from the Khronos Group, often called "the JPEG of 3D." It bundles geometry, materials, textures, and animation in a compact, runtime-ready form, and GLB is its single-file binary version used on the web and in AR.Files & formatsGPX (GPS track)GPX (GPS Exchange Format) is an XML format for GPS data — recorded tracks, routes, and waypoints. It is the universal way fitness apps, hiking devices, and navigation tools store and share where you went.Files & formatsGSM (audio)GSM audio is a speech codec from the GSM mobile-phone standard, designed to compress voice into a very small, low-bitrate stream. It is used for voicemail, VoIP, and telephony where bandwidth matters more than fidelity.Files & formatsGZIP (.gz)GZIP is a fast, single-file compressor that produces .gz files. It compresses one file at a time, so to pack a whole folder it is combined with TAR into a tar.gz. It is the default compression behind much of the web and Unix tooling.Files & formatsHAR (HTTP archive)A HAR (HTTP Archive) file is a JSON log of a browser’s network activity — every request and response, with timing, headers, and often content. Developers export it from browser dev tools to diagnose web performance and bugs.Files & formatsHDF5HDF5 (Hierarchical Data Format) is a format for storing large, complex scientific datasets in a single file. It organizes multidimensional arrays and metadata in a hierarchy, and is widely used in research, engineering, and machine learning.Files & formatsHDR (Radiance)HDR (Radiance) is a high-dynamic-range image format using the .hdr extension and an RGBE encoding that packs a shared exponent with red, green, and blue. It is widely used for lighting and environment maps in 3D rendering.Files & formatsHEIFHEIF (High Efficiency Image File Format) is the modern container behind the iPhone’s HEIC photos. It stores images at roughly half the size of JPEG at the same quality and can hold extras like depth maps and Live Photos — which is why switching to JPEG enlarges a library.Files & formatsHTMLHTML (HyperText Markup Language) is the standard text-based language that defines the structure and content of web pages, using tags like `<p>`, `<a>`, and `<img>`. Browsers read HTML and render it into the pages you see.Files & formatsHWP (Hangul)HWP is the document format of Hangul Word Processor (Hancom Office), the word processor widely used in South Korea, especially in government and education. The newer HWPX is an XML-based version of the same format.Files & formatsiCalendar (.ics)An iCalendar (.ics) file is the standard format for calendar data — events, invitations, and reminders. It is what email invites attach and what apps use to export and subscribe to calendars across platforms.Files & formatsICNS (Mac icon)ICNS is Apple’s icon format that bundles many sizes and resolutions of a single app icon into one file, so macOS can show it crisply everywhere from the Dock to a Finder list. It is the Mac counterpart to Windows’ ICO format.Files & formatsICO (icon file)ICO is the Windows icon file format. A single .ico file can hold the same icon at several sizes (such as 16×16, 32×32, 48×48, and 256×256), letting the system pick the right resolution for each context. It is also the classic format for website favicons.Files & formatsIFO (DVD info)IFO files are the small information files on a DVD-Video disc, stored in the VIDEO_TS folder. They tell the player where chapters, menus, subtitles, and audio tracks live inside the large VOB video files.Files & formatsINDD (Adobe InDesign)INDD is the native document format of Adobe InDesign, the page-layout app for brochures, magazines, books, and flyers. An INDD stores the full editable layout — text, frames, styles, and links to placed images — and is normally exported to PDF for sharing.Files & formatsINI fileAn INI file (`.ini`) is a simple plain-text configuration format that stores settings as `key=value` pairs, optionally grouped under `[section]` headers. It is easy to read and edit, and is common for app and Windows settings.Files & formatsIPA (iOS app archive)An IPA is the archive format that packages an iOS app for distribution. It is a ZIP file containing the app bundle, its resources, and signing data. You rarely see IPAs on a phone, since the App Store installs apps directly rather than handing you a file.Files & formatsISO (disk image)An ISO file is a disk image — an exact, single-file copy of an optical disc (CD/DVD) or its file system. You typically mount it as a virtual drive or extract its contents, rather than "installing" the ISO itself.Files & formatsIT (Impulse Tracker)IT (Impulse Tracker) is one of the most advanced classic tracker module formats. It extends MOD and XM with more channels, finer effects, and features like note-cut and resonant filters, while keeping files compact.Files & formatsJAR (Java archive)A JAR (Java Archive) packages compiled Java classes and resources into a single file for distribution. It is a ZIP archive with an added manifest, letting a whole Java library or application travel and run as one bundle.Files & formatsJFIFJFIF (JPEG File Interchange Format) is a standard way of packaging a JPEG image. A .jfif file is essentially a JPEG with a different extension, so it uses the same lossy compression and opens in the same apps — usually after renaming it to .jpg.Files & formatsJNGJNG (JPEG Network Graphics) is a niche image format that pairs JPEG-compressed photo data with a separate transparency channel. It was designed as a companion to PNG and MNG for cases where JPEG quality and an alpha channel were both needed.Files & formatsJPEGJPEG (.jpg) is the most widely supported photo format. It uses lossy compression to shrink photographs dramatically, trading a small amount of detail for much smaller files. It has no transparency and is larger than newer formats like HEIC or WebP at the same quality.Files & formatsJPEG 2000 (.jp2)JPEG 2000 (.jp2) is a wavelet-based image format designed to compress better than the original JPEG, with optional lossless mode and built-in support for high bit depths. Despite the quality advantage, browser and app support stayed thin, so it never replaced JPEG for everyday photos.Files & formatsJPEG XL (JXL)JPEG XL (JXL) is a modern image format designed to replace JPEG, offering both lossy and lossless compression, transparency, animation, and high dynamic range. It can store images at notably smaller sizes than JPEG at similar quality, but browser and app support is still limited.Files & formatsJSONJSON (JavaScript Object Notation) is a lightweight, text-based format for storing and exchanging structured data as key/value pairs and ordered lists. It is human-readable, language-independent, and the default format for most web APIs and config files.Files & formatsKeynote (Apple)A .key file is a presentation created in Apple Keynote, the slide app in Apple’s iWork suite. The format is Apple-only — Windows and Android cannot open it natively — so Keynote exports to PowerPoint, PDF, or video for sharing.Files & formatsKML / KMZKML (Keyhole Markup Language) is an XML format for geographic data — placemarks, paths, and overlays — made popular by Google Earth and Maps. KMZ is a zipped KML that bundles the map data with its images and icons.Files & formatsKRA (Krita)KRA is the native document format of Krita, the open-source painting app. It stores the complete editable project — layers, masks, vector and paint layers, and brush data — so KRA files are considerably larger than a flattened PNG or JPEG export.Files & formatsLIT (Microsoft Reader)LIT is the ebook format of Microsoft Reader, a discontinued e-reading app. A .lit file holds a formatted book, sometimes with DRM, but Microsoft Reader was retired, making LIT a legacy format you usually convert to EPUB.Files & formatsLOG file (.log)A LOG file (.log) is a plain-text record an app or operating system writes as it runs, logging events, errors, and activity with timestamps. Logs are useful for troubleshooting but can quietly pile up and take significant space over time.Files & formatsLWO (LightWave)LWO is the 3D object format of LightWave 3D, a modeling and rendering app long used in film and television. A .lwo file stores a model’s mesh geometry and surface (material) data.Files & formatsLZ4LZ4 is a lossless compression algorithm built for extreme speed rather than the smallest size. It compresses and decompresses very fast, which makes it popular inside filesystems, databases, and real-time systems.Files & formatsLZH / LHALZH (also called LHA) is an older compressed archive format that bundles and shrinks files, similar to ZIP. It was popular in Japan and on older systems, and remains common in retro software and some Japanese downloads.Files & formatsM2TS (Blu-ray)M2TS is the video container used on Blu-ray discs and by AVCHD camcorders, based on the MPEG-2 transport stream. It holds high-definition H.264 or MPEG-2 video plus multiple audio tracks, which makes M2TS files large and tricky to play outside media-savvy software.Files & formatsM2V (MPEG-2 video)M2V is an MPEG-2 video file that contains only the video stream — no audio. It is an "elementary stream" commonly used in DVD authoring, where video and audio are kept in separate files until they are multiplexed together.Files & formatsM4AM4A is an audio-only MPEG-4 file, the format the iPhone Voice Memos app and the iTunes/Apple Music store use. The extension is a container: most M4A files hold lossy AAC audio (small, MP3-like), but some hold lossless ALAC (large). It is the audio cousin of the MP4 video file.Files & formatsM4B (audiobook)M4B is an audio format built for audiobooks. It uses the same AAC audio and container as M4A, but adds chapter markers and bookmarking so a long recording can be navigated by chapter and resume where you stopped.Files & formatsM4P (protected AAC)M4P (.m4p) is a protected AAC audio file that carries DRM (digital rights management), historically sold by the older iTunes Store. The DRM ties playback to authorized Apple accounts and devices, so an .m4p will not play freely the way an unprotected .m4a or MP3 does.Files & formatsM4R (iPhone ringtone)M4R is Apple’s ringtone format — essentially an AAC audio file (the same encoding as M4A) with a .m4r extension, used for custom iPhone ringtones and alert tones. Ringtones are typically short, around 30 seconds or less.Files & formatsM4VM4V is Apple’s video container, nearly identical to MP4 but with optional FairPlay DRM copy protection. iTunes and the Apple TV app use it for purchased and rented video; DRM-free M4V files often play simply by renaming them to .mp4.Files & formatsMA/MB (Maya)MA and MB are the native scene formats of Autodesk Maya. MA (Maya ASCII) stores the scene as readable text, while MB (Maya Binary) stores the same scene in a compact binary form; both hold geometry, rigs, and animation.Files & formatsMarkdownMarkdown is a lightweight, plain-text formatting syntax that turns simple symbols into formatted text — `#` for headings, `*` for emphasis, and `-` for lists. It stays readable as raw text and converts cleanly to HTML.Files & formatsMDB (Access)MDB is the legacy Microsoft Access database format used before Access 2007, built on the Jet engine. A .mdb holds a full desktop database in one file and was replaced by the newer ACCDB format.Files & formatsMDF/MDS (disc image)MDF/MDS is a disc-image format created by Alcohol 120%. The MDF holds the actual disc data while the matching MDS file stores the layout and metadata, together preserving a CD or DVD as a file you can mount or burn.Files & formatsMIDIMIDI is not recorded audio — it is a set of instructions describing which notes to play, how loud, and for how long. The device’s synthesizer turns those instructions into sound. Because no waveform is stored, MIDI files are tiny, often just a few kilobytes for a full song.Files & formatsMKA (Matroska Audio)MKA (.mka) is the audio-only version of the Matroska container — a flexible wrapper that can hold many audio codecs, multiple tracks, and chapters in one file. The .mka itself is not a codec; the actual sound inside might be FLAC, AAC, MP3, Opus, or others.Files & formatsMKVMKV (Matroska) is an open, flexible video container that can hold an unlimited number of video, audio, subtitle, and chapter tracks in one file. It is common for movies and downloads but is not natively supported by iOS, so it often needs converting to MP4.Files & formatsMNG (animated PNG predecessor)MNG (Multiple-image Network Graphics) is an animation format from the PNG family, designed as a richer successor to animated GIF. It never gained broad browser or app support and is effectively obsolete, with APNG having become the practical animated-PNG standard.Files & formatsMOBI (Kindle ebook)MOBI is an ebook format originally from Mobipocket that Amazon adopted for early Kindle devices. It holds reflowable book text with chapters and basic formatting, but Amazon has retired it in favor of newer Kindle formats and no longer accepts MOBI uploads.Files & formatsMOD (tracker module)A MOD file is a "tracker module" — a music format that stores short instrument samples plus a sequence of notes telling the player when to trigger them. Originating on the Commodore Amiga, it packs full songs into tiny files.Files & formatsMOVMOV is Apple’s QuickTime video container, the default format iPhones and Macs record in. Like MP4 it wraps video and audio streams rather than defining quality, and on Apple devices it typically holds HEVC or H.264 video.Files & formatsMP3MP3 is a lossy audio format that shrinks music files by discarding sound details most people cannot hear. It is the most universally compatible audio format, though newer codecs like AAC achieve similar quality in smaller files.Files & formatsMP4MP4 (MPEG-4 Part 14) is the most common video container format. The .mp4 file holds video, audio, and subtitle streams together, but does not itself define quality — the codec inside (usually H.264 or HEVC) decides how large and how compressed the video is.Files & formatsMPEG (.mpg)MPEG (.mpg/.mpeg) refers to early video formats from the Moving Picture Experts Group — chiefly MPEG-1 and MPEG-2. MPEG-2 powered DVDs and digital TV; the .mpg files you find today are usually older, larger clips by modern standards.Files & formatsMPP (Project)MPP is the file format of Microsoft Project, used to store a project plan — tasks, schedules, dependencies, resources, and Gantt charts. It is proprietary to Project, so opening it outside the app usually needs a viewer or conversion.Files & formatsMSI (Windows installer)An MSI file is a Windows Installer package — a database of files, registry entries, and instructions that the Windows Installer service uses to install, repair, or remove a program cleanly.Files & formatsMSIX (Windows app)MSIX is a modern Windows app package format meant to replace older MSI and setup.exe installers. It installs apps in a clean, contained way so they can be cleanly uninstalled, and is the format used by many Microsoft Store apps.Files & formatsMTS / AVCHDMTS is the video file produced by AVCHD, a high-definition format used by many camcorders and digital cameras. AVCHD records H.264 video in an MPEG transport stream, giving good HD quality but large files and limited playback support outside dedicated video software.Files & formatsMusepack (.mpc)Musepack (.mpc) is an open, lossy audio format optimized for high-quality music at higher bitrates. It has a dedicated audiophile following but limited device and app support, so it is far less common than MP3 or AAC.Files & formatsMXF (broadcast)MXF (Material Exchange Format) is a professional container used in broadcast and film production to wrap video, audio, and rich metadata together. It is built for editing and archiving workflows rather than playback, so consumer devices rarely open it directly.Files & formatsNDJSON / JSONLNDJSON (newline-delimited JSON), also called JSON Lines or JSONL, stores one JSON object per line. This makes it easy to stream, append, and process large datasets record by record without loading the whole file at once.Files & formatsNEF (Nikon RAW)NEF (Nikon Electronic Format) is Nikon’s RAW image format, storing the unprocessed sensor data from Nikon cameras. Files are large (often 20–50 MB) and need Nikon’s software, Lightroom/Adobe Camera Raw, or conversion to DNG or JPEG to edit and share.Files & formatsNRGNRG is a proprietary optical-disc image format created by Nero Burning ROM. Like an ISO, a single .nrg file holds the full contents of a CD or DVD so it can be mounted or burned, but it can also store extra disc details and multiple tracks.Files & formatsNumbers (Apple)A .numbers file is a spreadsheet created in Apple Numbers, the spreadsheet app in Apple’s iWork suite. The format is Apple-only — Windows and Android cannot open it natively — so Numbers exports to Excel, CSV, or PDF for sharing.Files & formatsOBJ (3D model)OBJ is a plain-text 3D geometry format that stores a model’s vertices, faces, and texture coordinates. It is one of the most widely supported interchange formats, but it carries no animation and stores materials in a separate .mtl file.Files & formatsODP (OpenDocument Presentation)ODP is the OpenDocument Presentation format — an open, ISO-standardized slide-deck file used by default in LibreOffice Impress and other open-source office suites. It is the free, vendor-neutral counterpart to Microsoft PowerPoint’s PPTX.Files & formatsODS (OpenDocument Spreadsheet)ODS is the OpenDocument Spreadsheet format — an open, ISO-standardized spreadsheet file used by default in LibreOffice Calc and other open-source office suites. It is the free, vendor-neutral counterpart to Microsoft Excel’s XLSX.Files & formatsODT (OpenDocument Text)ODT is the OpenDocument Text format — an open, ISO-standardized word-processing file used by default in LibreOffice Writer and other open-source office suites. It is the free, vendor-neutral counterpart to Microsoft Word’s DOCX.Files & formatsOGA (Ogg audio)OGA (.oga) is the audio-only extension for the open Ogg container, used to signal that a file holds sound rather than video. The audio inside is usually Vorbis, Opus, or FLAC. Many systems handle .oga the same as .ogg, and both are commonly converted to MP3 for wider device support.Files & formatsOggOgg is a free, open container format that wraps compressed audio — most often Vorbis or Opus. The `.ogg` extension tells you the wrapper, not the exact codec inside, so two Ogg files can hold quite different audio. The contents are usually lossy, so files stay small.Files & formatsOGV (Ogg video)OGV is a video file in the Ogg container, an open, royalty-free format typically pairing Theora video with Vorbis audio. It was created for the open web, but modern sites favor more efficient formats like WebM and MP4, so OGV is now uncommon.Files & formatsONE (OneNote)ONE is the file format Microsoft OneNote uses to store a notebook section — typed and handwritten notes, images, and clippings on freeform pages. Modern OneNote keeps notebooks in the cloud, so loose .one files are mostly local or exported copies.Files & formatsOPF (ebook package)OPF (Open Packaging Format) is the XML manifest at the heart of an EPUB ebook. It lists every file in the book, sets the reading order, and stores metadata like title and author — the table of contents the reader software follows.Files & formatsOpusOpus is a modern, lossy audio format built for high quality at low bitrates. It sounds clearer than MP3 or AAC at the same file size, which is why messaging apps and streaming use it for voice notes and music. It is not lossless, so some original data is discarded.Files & formatsORF (Olympus RAW)ORF (Olympus Raw Format) is the RAW image format used by Olympus and OM System cameras, holding unprocessed sensor data. Files are large (often 15–30 MB) and need the maker’s software, Lightroom/Adobe Camera Raw, or conversion to DNG or JPEG to edit and share.Files & formatsOTF (OpenType font)OTF (OpenType) is a modern, cross-platform font format from Adobe and Microsoft. It stores scalable outlines like TrueType but adds advanced typography — ligatures, alternates, and small caps — making it the common choice for professional type.Files & formatsPages (Apple)A .pages file is a document created in Apple Pages, the word processor in Apple’s iWork suite. The format is Apple-only — Windows and Android cannot open it natively — so Pages exports to Word, PDF, or other formats for sharing.Files & formatsParquetParquet is an open columnar storage format for large datasets, widely used in data analytics and big-data tools. By storing data column by column with compression, it makes analytical queries fast and files much smaller than CSV.Files & formatsPBMPBM (Portable Bitmap) is the black-and-white member of the Netpbm family. It stores a 1-bit image — each pixel is simply on or off — in a deliberately simple format that is easy for programs to read and write.Files & formatsPCMPCM (Pulse-Code Modulation) is raw, uncompressed digital audio — the actual samples of the sound wave with no compression at all. It is the highest-fidelity form and the largest, and it is the underlying audio inside WAV and AIFF files. Lossy formats like MP3 are built by compressing PCM.Files & formatsPCXPCX is one of the oldest PC image formats, created by ZSoft for PC Paintbrush in the 1980s. It uses simple run-length encoding and was common in DOS-era graphics before GIF, PNG, and JPEG took over.Files & formatsPDB (Palm/ebook)PDB (Palm Database) is a container format from Palm OS used for many things, including ebooks read in apps like eReader and PalmDOC. As an ebook format it is legacy, and books are usually converted to EPUB or MOBI.Files & formatsPDFPDF (Portable Document Format) is a fixed-layout document format that looks the same on any device. Most PDFs are small, but scanned documents and image-heavy files can grow large, and they accumulate quietly in Downloads and the Files app.Files & formatsPDF encryption (password)PDF encryption scrambles a PDF’s contents so it can only be opened or edited with the correct password. There are two kinds: a user password to open the document and an owner password that restricts actions like printing, copying, or editing.Files & formatsPDF/A (archival PDF)PDF/A is a version of the PDF format designed for long-term archiving. It requires everything needed to display the document — fonts, color, and images — to be embedded in the file, so it looks the same decades from now, at the cost of a somewhat larger file.Files & formatsPEF (Pentax RAW)PEF (Pentax Electronic Format) is Pentax’s RAW image format, storing unprocessed sensor data from Pentax cameras. Files are large and need Pentax’s software, Lightroom/Adobe Camera Raw, or conversion to DNG or JPEG to edit and share.Files & formatsPFB (PostScript font)PFB (Printer Font Binary) is the binary container for a PostScript Type 1 font’s outline data. It holds the actual glyph shapes and usually travels with a separate metrics file before being installed.Files & formatsPFM (font metrics)PFM (Printer Font Metrics) is the companion file to a PostScript Type 1 font on Windows. It stores spacing, kerning, and character-width data, while the matching PFB file holds the actual glyph outlines.Files & formatsPGMPGM (Portable Graymap) is the grayscale member of the Netpbm family. It stores an image as gray levels per pixel in a simple, easy-to-parse layout, making it a common intermediate format in image processing.Files & formatsPKG (installer)A PKG file is a macOS installer package. It bundles an app or system component plus scripts that copy files into place and configure them, so double-clicking runs a guided installer rather than just dragging an app to Applications.Files & formatsPlain text (.txt)A plain-text file (`.txt`) contains only unformatted text — characters with no fonts, colors, images, or layout. It is the simplest, most universal document format, readable by virtually any device or program.Files & formatsPLIST (property list)A PLIST (property list, .plist) is an Apple file that stores settings and configuration as structured key–value data, in either human-readable XML or a compact binary form. macOS and iOS apps use them for preferences, app metadata, and launch settings.Files & formatsPLY (Polygon)PLY (Polygon File Format, or Stanford Triangle Format) is a 3D format for storing meshes and point clouds. It records vertices and faces along with extras like color and normals, and is common in 3D scanning and research.Files & formatsPNGPNG (.png) is a lossless image format that keeps every pixel exact and supports transparency. That makes it ideal for screenshots, logos, and graphics, but files are much larger than JPEG or WebP — so a folder full of PNG screenshots can quietly fill storage.Files & formatsPostScript Type 1 fontPostScript Type 1 is an early scalable font format from Adobe that defined professional digital type for desktop publishing. It uses outline glyphs but has been deprecated in modern software in favor of OpenType.Files & formatsPPMPPM (Portable Pixmap) is the full-color member of the Netpbm family. It stores red, green, and blue values per pixel in a simple, uncompressed layout, making it a handy intermediate format in image-processing pipelines.Files & formatsPPTX (PowerPoint)PPTX is the default file format for Microsoft PowerPoint presentations since PowerPoint 2007. It is a ZIP package of XML and media, and because slide decks lean heavily on images and video, PPTX files are often the largest of the Office formats.Files & formatsPRC (Mobipocket)PRC is an ebook file most often associated with Mobipocket, the technology behind early Kindle books. A .prc file is closely related to MOBI and was readable on Palm and early Kindle devices; modern readers prefer EPUB or AZW3.Files & formatsProRes (Apple)ProRes is Apple’s professional video codec, designed for editing rather than small file sizes. It uses light compression to keep near-original quality and easy scrubbing in editors, which makes ProRes recordings far larger than the H.264 or HEVC clips phones normally save.Files & formatsPS (PostScript)PostScript (.ps) is a page-description language from Adobe that tells a printer or renderer exactly how to draw each page — text, vector graphics, and images. PDF evolved from PostScript and has largely replaced it for everyday documents.Files & formatsPSB (large Photoshop)PSB (Large Document Format) is Photoshop’s file type for documents too big for the standard PSD — beyond 30,000 pixels per side or 2 GB in size. It stores the same editable layers as a PSD but is built for huge canvases, so PSB files are often very large.Files & formatsPSD (Photoshop document)PSD (Photoshop Document) is Adobe Photoshop’s native file format. It preserves a full editable project — layers, masks, text, smart objects, and effects — which makes it powerful for editing but much larger than a flattened JPEG or PNG export.Files & formatsPUB (Publisher)PUB is the file format of Microsoft Publisher, a desktop-publishing app for flyers, newsletters, and brochures. The format is proprietary to Publisher, so other programs open it poorly — most people export to PDF for sharing.Files & formatsQCOW2QCOW2 (QEMU Copy-On-Write, version 2) is the native virtual-disk format for QEMU and KVM. A single .qcow2 file holds a virtual machine’s entire disk and supports features like snapshots, compression, and growing on demand instead of reserving full size up front.Files & formatsRAF (Fujifilm RAW)RAF is Fujifilm’s RAW image format, storing the unprocessed sensor data from Fujifilm cameras. Files are large (often 25–60 MB) and need Fujifilm’s software, Lightroom/Adobe Camera Raw, or conversion to DNG or JPEG to edit and share.Files & formatsRARRAR is a proprietary archive format with strong compression, created by the WinRAR tool. You can extract .rar files with WinRAR, 7-Zip, or The Unarchiver, but creating new RAR archives requires WinRAR (or its command-line tool).Files & formatsRAW imageA RAW image is the unprocessed data straight from a camera sensor, before any in-camera compression or color processing. It preserves maximum editing flexibility but produces very large files — many times bigger than a JPEG or HEIC of the same shot.Files & formatsRealAudio (.ra)RealAudio (.ra, also .rm) is an early streaming audio format from RealNetworks, designed in the 1990s to play sound over slow dial-up connections. It is largely obsolete today and most current players need a converter or RealPlayer to open it.Files & formatsREG (Windows Registry file)A REG file (.reg) is a Windows Registry export — a text file containing registry keys and values. Double-clicking one merges those settings into the Windows Registry, which makes .reg files powerful but risky: a bad one can change critical system settings.Files & formatsRMVB / RM (RealMedia)RM and RMVB are RealMedia container formats from RealNetworks, built for low-bitrate internet streaming in the late 1990s and 2000s. RMVB ("variable bitrate") was popular for compact movie downloads but is now a legacy format most modern players need a plug-in or conversion to open.Files & formatsRPM (Red Hat package)An RPM is the software package format used by Red Hat, Fedora, and related Linux distributions. It bundles a program’s files along with version data, dependency information, and install scripts, managed by tools like dnf or rpm.Files & formatsRTFRTF (Rich Text Format) is a plain-text document format that encodes basic formatting — bold, italics, fonts, and colors — using readable markup. It opens in almost any word processor on any platform, which makes it a reliable lowest-common-denominator for portable formatted text.Files & formatsRW2 (Panasonic RAW)RW2 is Panasonic’s RAW image format, used by Lumix cameras to store unprocessed sensor data. Files are large (often 15–30 MB) and need Panasonic’s software, Lightroom/Adobe Camera Raw, or conversion to DNG or JPEG to edit and share.Files & formatsSearchable PDFA searchable PDF is a scanned document that has a hidden, selectable text layer added by OCR (optical character recognition) beneath the page image. You see the original scan, but you can search, select, and copy the recognized text — unlike a plain image-only scan.Files & formatsSFD (FontForge)SFD (Spline Font Database) is the native source format of FontForge, the open-source font editor. It stores a font project’s glyph outlines and settings as editable text, separate from the finished TTF or OTF you export.Files & formatsSGI / RGB imageSGI is a raster image format from Silicon Graphics, using extensions like .sgi, .rgb, and .rgba. It was a standard on SGI workstations and still appears in older VFX and 3D pipelines.Files & formatsSKP (SketchUp)SKP is the native file format of SketchUp, a 3D modeling app popular in architecture, interior design, and woodworking. A .skp file stores the model’s geometry, components, materials, and scenes.Files & formatsSparse image (Mac)A sparse image is a macOS disk-image type that only uses as much real storage as the data it actually contains, growing as you add files. It is used for encrypted containers and for backups like Time Machine over a network.Files & formatsSpeex (.spx)Speex (.spx) is an open, lossy audio codec designed specifically for speech — voice chat, VoIP, and voice memos — rather than music. It produces very small files at low bitrates but is now largely superseded by Opus, which handles both speech and music better.Files & formatsSQL file (.sql)A SQL file (`.sql`) is a plain-text file containing SQL statements — commands that create tables, insert rows, or query a database. It is commonly used to back up, transfer, or rebuild a database by running its statements in order.Files & formatsSQLiteSQLite is a self-contained database that stores an entire database — tables, indexes, and data — in a single file, typically ending in .sqlite, .sqlite3, or .db. Countless apps embed it to hold their data locally, which is why a SQLite file is often where an app’s settings, history, and content live.Files & formatsSRT (SubRip subtitles)An SRT file is a plain-text subtitle file in the SubRip format. It lists numbered captions, each with a start and end timecode and the line of text to show, so a player can overlay subtitles on a video. Because it is just text, an SRT file is tiny — usually a few kilobytes.Files & formatsSRW (Samsung RAW)SRW is Samsung’s RAW image format, used by Samsung NX cameras to store unprocessed sensor data. Files are large and need Samsung’s software, Lightroom/Adobe Camera Raw, or conversion to DNG or JPEG to edit and share.Files & formatsSTEP (.stp CAD)STEP (.step or .stp) is an open, international-standard format for sharing precise 3D CAD models between programs. Unlike a triangle mesh, it stores exact solid and surface geometry, making it the common neutral format for mechanical and product design.Files & formatsSTL (3D printing)STL is the standard file format for 3D printing. It describes a model’s surface as a mesh of triangles, with no color, texture, or units — just the geometry a slicer needs to turn into printer instructions.Files & formatsStuffIt (.sit/.sitx)StuffIt (.sit, later .sitx) is a compressed archive format that was the standard way to pack files on classic Mac OS. It bundled and shrank files much like ZIP, and is now legacy, replaced by built-in ZIP support on the Mac.Files & formatsSVGSVG (.svg) is a vector image format that stores shapes as math rather than pixels, so it scales to any size without losing sharpness. For logos and icons it is usually tiny, but it is unsuited to photographs, which it cannot represent efficiently.Files & formatsSWF (Flash)SWF (Small Web Format, originally Shockwave Flash) is Adobe Flash’s file format for vector animations, interactive content, and games that ran in the Flash Player. With Flash discontinued at the end of 2020, SWF is a deprecated format browsers no longer support.Files & formatsTARTAR (tape archive) bundles many files and folders into one .tar file but does not compress them on its own. It is almost always paired with a compressor, producing combinations like tar.gz (gzip) or tar.xz.Files & formatsTEX (LaTeX)A .tex file is the plain-text source for a TeX or LaTeX document — a markup language used to typeset technical and academic writing. You compile the .tex with a TeX engine to produce a polished PDF, especially for math-heavy papers.Files & formatsTGA (Targa)TGA (Targa) is a legacy raster image format that supports an alpha channel for transparency. Once common for graphics and game textures, it stores images with little or no compression, so files are large compared to PNG or modern formats.Files & formatsTGZ (.tar.gz)A TGZ (.tgz or .tar.gz) is a tar archive that has been compressed with gzip. The tar step bundles many files and folders into one, and gzip shrinks the result — the standard way to package software and backups on Unix and Linux.Files & formatsTIFFTIFF (.tif/.tiff) is a high-quality image format used in photography, scanning, and printing. It is typically lossless and stores full detail, which makes files very large — often many times the size of a JPEG of the same image.Files & formatsToast (.toast)A .toast file is a disc image created by Roxio Toast, a popular Mac CD/DVD burning app. It stores the contents and layout of a disc so it can be burned or mounted later, similar to an ISO on the Mac.Files & formatsTOML (config)TOML (.toml) is a human-readable configuration file format built around simple key = value lines grouped into [sections]. It is designed to be easy to read and write by hand, and is common in developer tooling for project and app settings.Files & formatsTRP / TS recordingTRP is a transport-stream video file, typically a digital or HDTV broadcast recording captured by a set-top box or smart TV. It is a variant of the MPEG transport stream (.ts) used for over-the-air and cable recordings.Files & formatsTS (MPEG transport stream)TS (MPEG transport stream) is a container built for broadcasting and streaming, where video is split into small packets that can survive transmission errors. It is used by digital TV and HLS streaming, often as many .ts segment files.Files & formatsTSVTSV (tab-separated values) is a plain-text format for tabular data where each line is a row and a Tab character separates the columns. It works like CSV but uses tabs instead of commas as the field delimiter.Files & formatsTTF (TrueType font)TTF (TrueType) is a widely supported font file format developed by Apple and Microsoft. It stores letter shapes as scalable outlines so text stays sharp at any size, and a single TTF holds one font style such as Regular or Bold.Files & formatsTTMLTTML (Timed Text Markup Language) is an XML-based format for captions and subtitles, used in broadcast and streaming. It pairs timed text with styling and layout, and underlies profiles like SMPTE-TT and the IMSC captions used by streaming services.Files & formatsUFO (font source)UFO (Unified Font Object) is an open, editable source format for fonts. Rather than a finished file, a .ufo is a folder of XML files describing every glyph and setting, used by type designers before exporting to TTF or OTF.Files & formatsUSDZ (AR)USDZ is a 3D file format Apple uses for augmented reality on iPhone and iPad. It packages a USD scene and its textures into a single file that opens in AR Quick Look, letting you place a 3D object in your real space.Files & formatsvCard (.vcf)A vCard (.vcf) is the standard file format for contact information — name, phone, email, and address. It is how phones and address books export and share contacts, and a single .vcf can hold one or many cards.Files & formatsVDIVDI (VirtualBox Disk Image) is the native virtual hard-disk format for Oracle VirtualBox. A single .vdi file represents an entire virtual machine’s disk — its operating system, programs, and files — so it can be very large and grows as the VM is used.Files & formatsVHD/VHDX (virtual hard disk)A VHD (and its successor VHDX) is a single file that acts as a complete virtual hard disk, holding its own partitions and file system. Windows and virtual machines use it as a self-contained disk image. These files can grow very large as their contents fill up.Files & formatsVMDK (VMware disk)A VMDK is the virtual disk format created by VMware. The file stores a virtual machine’s entire drive — its partitions, file system, and data — as a self-contained disk image, and it can occupy a large amount of space on the host computer.Files & formatsVOB (DVD video)VOB (Video Object) is the container used to store video, audio, subtitles, and menus on DVDs. Found in the VIDEO_TS folder, VOB files hold MPEG-2 video and are capped at 1 GB each, so a DVD movie is split across several numbered .vob files.Files & formatsVOX (Dialogic audio)VOX is a low-bitrate audio format using Dialogic ADPCM compression, built for telephony — voicemail, IVR prompts, and call recordings. It is raw audio with no header, so you usually need to know the sample rate to play it correctly.Files & formatsVRML / WRLVRML (Virtual Reality Modeling Language), saved as .wrl files, is an early text-based format for 3D scenes on the web. It described interactive 3D worlds in the 1990s and was later succeeded by X3D.Files & formatsVSD / VSDX (Visio)VSD and the newer VSDX are the diagram formats used by Microsoft Visio for flowcharts, network maps, org charts, and floor plans. VSDX is a modern ZIP-and-XML format; the older VSD is binary and proprietary.Files & formatsWAR (Java web archive)A WAR (Web Application Archive) is a ZIP-based package that bundles a Java web application — its code, pages, and configuration — into one file for deployment to a Java application server like Tomcat.Files & formatsWASM (WebAssembly)WASM (WebAssembly) is a compact binary instruction format that runs in web browsers at near-native speed. A .wasm file is compiled code — often from C, C++, or Rust — that the browser executes alongside JavaScript.Files & formatsWAVWAV (WAVE) is an uncompressed audio format that stores raw PCM sound at full quality. That makes it ideal for editing and mastering, but the files are large — far bigger than MP3 or AAC for the same audio.Files & formatsWavPack (.wv)WavPack (.wv) is an open lossless audio format that compresses audio with no quality loss and can also store a lossy version plus a small correction file. It plays back identical to the original, but support is limited outside dedicated players, so it is often converted to FLAC or MP3.Files & formatsWBMPWBMP (Wireless Bitmap) is a monochrome image format designed for early WAP mobile phones. It stores a simple black-and-white image with no color or grayscale, making files tiny for slow mobile connections.Files & formatsWebMWebM is an open, royalty-free video container designed for the web, built around the VP8/VP9 (or AV1) video codecs and Opus/Vorbis audio. It is widely used by browsers and sites like YouTube for efficient streaming.Files & formatsWebPWebP (.webp) is a modern Google image format that supports both lossy and lossless compression, transparency, and animation in one file. It produces noticeably smaller files than JPEG or PNG at similar quality, so it is widely used on the web and increasingly on Android.Files & formatsWebVTT (.vtt subtitles)A VTT (WebVTT) file is a plain-text caption and subtitle format built for web video, used by the HTML5 video player. Like SRT it stores timecoded text, but it adds styling, positioning, and metadata. It is a small text file, typically only a few kilobytes.Files & formatsWIM (Windows image)WIM (Windows Imaging Format) is a file-based disk-image format Microsoft uses to deploy Windows. Unlike sector-based images, it stores files individually, so one WIM can hold multiple Windows editions and reuse identical files to save space.Files & formatsWMAWMA (Windows Media Audio) is Microsoft’s audio format, designed as a lossy alternative to MP3 with similar file sizes and quality. It is now largely legacy: most playback has moved to MP3 and AAC, and many non-Windows devices cannot open WMA without converting it first.Files & formatsWMV (Windows Media Video)WMV (Windows Media Video) is Microsoft’s video format, once standard on Windows and in Windows Media Player. It plays natively on Windows but has limited support elsewhere, so WMV files often need converting for Macs, phones, and the web.Files & formatsWOFF (web font)WOFF (Web Open Font Format) is a compressed font format made for the web. It wraps a TrueType or OpenType font with compression and metadata so it downloads faster on a webpage, which is why sites serve WOFF rather than raw TTF or OTF.Files & formatsWOFF2 (web font)WOFF2 is the current web-font format and the successor to WOFF. It uses stronger compression to make font files smaller, so webpages download custom typefaces faster. It is the format most modern websites serve by default.Files & formatsWPD (WordPerfect)WPD is the document format created by Corel WordPerfect, one of the dominant word processors of the 1980s and 1990s. It stores formatted text, and the format is still maintained by WordPerfect today, though most workflows have moved to DOCX.Files & formatsWPS (Microsoft Works)WPS is the word-processor document format from Microsoft Works, a discontinued low-cost office suite bundled with many home PCs. A .wps file holds formatted text, but Works was retired, so the format is now legacy.Files & formatsWTV / DVR-MSWTV (and its predecessor DVR-MS) is the recorded-TV format used by Windows Media Center. These files hold broadcast video and audio plus metadata, and are large because they store TV recordings, often at full broadcast quality.Files & formatsX3F (Sigma RAW)X3F is Sigma’s RAW image format, used by Sigma cameras with Foveon sensors to store unprocessed sensor data. Files are large and need Sigma’s own software — most other editors and converters cannot open X3F directly without it.Files & formatsXAPK (Android bundle)An XAPK is a packaging format used by third-party Android app sites to bundle an APK together with its extra data — split APKs or large OBB asset files — in a single download. It is not an official Google format.Files & formatsXBMXBM (X BitMap) is a monochrome image format from the X Window System that is written as C source code. The file is literally a small C array defining a 1-bit image, which made it easy to compile icons directly into programs.Files & formatsXCF (GIMP)XCF is the native project format of the GIMP image editor. It saves your full working document — layers, masks, paths, selections, and editing state — rather than a flattened picture, so XCF files are much larger than the JPEG or PNG you export from them.Files & formatsXLSX (Excel)XLSX is the default file format for Microsoft Excel spreadsheets since Excel 2007. Like DOCX, it is a ZIP package of XML, so even large data tables stay compact unless they hold embedded charts, images, or heavy formatting.Files & formatsXM (tracker)XM (Extended Module) is a tracker music format introduced with FastTracker 2. It extends the older MOD format with more channels, multi-sample instruments, and volume envelopes, while keeping files small.Files & formatsXMLXML (Extensible Markup Language) is a text-based format that stores structured data inside nested, custom-named tags, such as `<title>…</title>`. It is self-describing and widely used for documents, configuration, RSS feeds, and data exchange between systems.Files & formatsXPMXPM (X PixMap) is a color image format from the X Window System, also written as C source code. It maps each character in a text grid to a color, letting developers embed small color icons directly into programs.Files & formatsXPS / OXPSXPS (XML Paper Specification) is Microsoft’s fixed-layout document format, created as a Windows alternative to PDF. OXPS is the newer OpenXPS variant. Both preserve a page exactly as designed, but PDF is far more widely supported.Files & formatsXvidXvid is a free, open-source MPEG-4 Part 2 video codec created as an alternative to DivX. It was widely used in the 2000s to compress movies into small AVI files and is now a legacy codec replaced by H.264 for most new video.Files & formatsXZXZ is a single-file compressor that uses LZMA2 to reach a very high compression ratio — typically the smallest of the common Unix formats. It pairs with TAR as tar.xz and is widely used for software releases and Linux packages.Files & formatsY4M (raw YUV4MPEG)Y4M (YUV4MPEG2) is an uncompressed video format that stores raw YUV frames with a simple text header. Because nothing is compressed, files are extremely large; it is used as an intermediate format for encoding and codec testing, not for everyday storage or playback.Files & formatsYAMLYAML is a human-readable, text-based data format that uses indentation instead of brackets to show structure. It is popular for configuration files because it is easy to read and write by hand, and it is a superset of JSON.Files & formatsZ (Unix compress)A .Z file is the output of the classic Unix "compress" command, which uses LZW compression to shrink a single file. It is an old format that predates gzip and is now largely replaced by gzip (.gz) and other tools.Files & formatsZIP archiveA ZIP archive bundles one or more files into a single compressed .zip file that is smaller and easier to share. Unzipping it creates a second, full-size copy of the contents — so an archive and its extracted files can both take up space at once.Files & formatsZstandard (.zst)Zstandard (zstd) is a modern, lossless compression method designed for fast speed at strong compression ratios. Files compressed with it use the `.zst` extension, and it is widely used in software packaging, file systems, and backups.Files & formatsZTL (ZBrush)ZTL is the native tool format of ZBrush, a digital sculpting app used for highly detailed 3D models. A .ztl saves a sculpted "tool" with its high-resolution detail and subdivision levels, meant to be reopened in ZBrush.
Editing & tools 21
What the browser tools do — compression, conversion, redaction, and OCR.
Editing & toolsBackground removalBackground removal separates the main subject of a photo from everything behind it, leaving a clean cutout you can place on a transparent, white, or new background. Modern tools do this automatically by detecting the subject’s edges, which is ideal for product shots, profile pictures, and graphics.Editing & toolsBatch image resizingBatch image resizing changes the pixel dimensions of many images in one operation, applying the same target size, percentage, or fit rule to every file. It saves time and keeps a set of images consistent for the web, email, or upload limits.Editing & toolsColor quantizationColor quantization reduces the number of distinct colors in an image to a smaller palette, mapping each pixel to the nearest remaining color. It is how an 8-bit PNG shrinks: fewer colors means a smaller file, at the cost of some color accuracy and possible banding.Editing & toolsDPI vs PPIDPI (dots per inch) describes how many ink dots a printer lays down per inch, while PPI (pixels per inch) describes how many pixels fit in an inch of a digital image or screen. DPI is a print measurement; PPI is a screen and source-image measurement, and the two are often used interchangeably but mean different things.Editing & toolsFile format conversionFile format conversion re-encodes a file from one type to another — for example HEIC to JPEG, PNG to WebP, or one color profile to another — so it opens where you need it. Conversion can change file size and compatibility, and it often strips metadata in the process.Editing & toolsGIF optimizationGIF optimization shrinks an animated GIF’s file size by reducing colors, dropping or merging frames, and trimming unchanged pixels between frames. Because GIFs compress poorly by nature, optimization is often what makes one small enough to share or embed.Editing & toolsImage compressionImage compression shrinks a photo’s file size by removing redundant or less-visible data. Lossy compression (JPEG, WebP) drops fine detail for big savings; lossless compression (PNG) keeps every pixel but saves less. It is the fastest way to make images smaller for sharing, email, or the web.Editing & toolsImage croppingCropping removes the outer parts of an image to reframe the subject, change the aspect ratio, or cut out unwanted areas. Unlike resizing, it discards part of the picture rather than scaling the whole thing, so it changes composition and dimensions but not the remaining pixels’ detail.Editing & toolsImage redactionImage redaction permanently hides sensitive information in a photo or screenshot — names, account numbers, faces, addresses — by covering it and flattening the result so the hidden data cannot be recovered. Done correctly, the original pixels are destroyed, not just visually masked.Editing & toolsImage to PDFConverting an image to PDF wraps one or more photos — JPEGs, PNGs, or scans — into a single PDF document with fixed pages. It is the standard way to bundle receipts, IDs, or scanned pages into one portable, printable file that opens the same on any device.Editing & toolsImage upscalingImage upscaling increases an image’s pixel dimensions by generating new pixels between the originals. Classic methods interpolate from neighboring pixels; AI upscalers predict plausible detail from training data. Neither truly recovers detail the original never captured.Editing & toolsOCR (optical character recognition)OCR (optical character recognition) reads the text inside an image or scanned document and turns it into real, selectable, editable text. It converts a picture of words — a photo, screenshot, or scanned PDF — into characters you can copy, search, and edit.Editing & toolsPDF compressionPDF compression reduces a PDF’s file size, mostly by re-compressing and downsampling the images inside it. It is the standard fix for a PDF that is too large to email or upload, and it keeps the document’s text, layout, and pages intact.Editing & toolsPixelationPixelation obscures part of an image by averaging it into large blocky squares, hiding faces, plates, or text behind a mosaic. It is a quick way to censor a region — but for truly sensitive data a solid block is safer, since heavy pixelation of text can sometimes be reversed.Editing & toolsProduct photoA product photo is an image of an item prepared for selling online — typically a single product shown clearly, often on a clean or white background, sized and formatted to a marketplace’s requirements. Good product images are consistent, sharp, and free of distracting backgrounds.Editing & toolsProgressive JPEGA progressive JPEG loads as a full-size but blurry image that sharpens in successive passes, instead of drawing top-to-bottom like a baseline JPEG. Both store the same photo; progressive encoding mainly changes how the image appears while it downloads, and can be slightly smaller for large images.Editing & toolsThumbnailA thumbnail is a small preview image that represents a larger image, video, or file. It loads quickly in lists and grids, and for videos it is often a custom-designed cover image meant to attract clicks rather than an automatic frame grab.Editing & toolsTransparent backgroundA transparent background means part of an image has no color at all, so whatever sits behind it shows through. It relies on an alpha channel and must be saved as a format that supports transparency — usually PNG or WebP — since JPEG cannot store it.Editing & toolsVideo to GIFConverting a video to a GIF turns a short clip into a silent, looping animation that plays automatically anywhere images do. GIFs are great for reactions and short loops but drop sound, use only 256 colors, and can be surprisingly large, so keep clips brief.Editing & toolsWatermarkA watermark is text, a logo, or a pattern overlaid on an image or document to mark ownership, signal status (such as "Draft" or "Confidential"), or discourage unauthorized reuse. It can be visible and semi-transparent, or invisible and embedded in the file.Editing & toolsWhite background (product photo)A white background is a plain, uniform white field behind a product, required by many marketplaces so items appear clean and consistent. It is created by shooting against white or by removing the original background and placing the product on a solid white layer.
Web & SEO 23
Web, metadata, and SEO terms behind the marketing and link tools.
Web & SEOAlt textAlt text is a short written description added to an image with the HTML alt attribute. Screen readers read it aloud for people who cannot see the image, browsers show it when an image fails to load, and search engines use it to understand and rank images.Web & SEOBase64 encodingBase64 is a way to represent binary data — like an image or file — using only printable text characters. It lets you embed a file directly inside HTML, CSS, or JSON as a data URI, at the cost of making the data about a third larger than the original.Web & SEOCanonical tagA canonical tag is an HTML element — <link rel="canonical" href="..."> — that tells search engines which URL is the preferred version of a page when several URLs show the same or similar content. It consolidates ranking signals onto one URL and prevents duplicate-content dilution.Web & SEOCore Web VitalsCore Web Vitals are Google's standardized metrics for real-world page experience: Largest Contentful Paint (loading), Interaction to Next Paint (responsiveness), and Cumulative Layout Shift (visual stability). They factor into ranking.Web & SEOCumulative Layout Shift (CLS)Cumulative Layout Shift (CLS) is a Core Web Vitals metric that measures how much visible content unexpectedly moves while a page loads. Lower is better; Google treats a score of 0.1 or below as good.Web & SEODefinedTerm SchemaDefinedTerm is a Schema.org type that marks up a glossary entry — its name, description, and parent term set — so search engines and AI answer engines can identify a page as the authoritative definition of a specific term.Web & SEOFAQPage SchemaFAQPage is a Schema.org type that marks up a list of question-and-answer pairs so search engines and AI answer engines can read a page's FAQ. Each entry uses Question with an acceptedAnswer.Web & SEOFeatured SnippetA featured snippet is a short answer that Google extracts from a web page and displays in a highlighted box at the top of the search results, above the regular blue links. It aims to answer a query directly, citing the source page's title and URL so users can click through for more.Web & SEOHowTo SchemaHowTo schema is schema.org structured data that marks up step-by-step instructions, letting search engines understand a guide's steps, tools, and supplies. Google deprecated HowTo rich results in 2023, but the markup still aids semantic understanding and AI answers.Web & SEOHTTP redirect (301 vs 302)An HTTP redirect sends visitors and search engines from one URL to another. A 301 is a permanent move that passes ranking signals to the new URL; a 302 is a temporary move that keeps the original URL indexed. Choosing the wrong one can lose or scatter SEO value.Web & SEOImage CDNAn image CDN is a content delivery network that stores, transforms, and serves images from edge servers close to the user. It can resize, re-encode, and compress images on the fly via URL parameters, then cache the result for fast, format-optimized delivery.Web & SEOInteraction to Next Paint (INP)Interaction to Next Paint (INP) is a Core Web Vital that measures how quickly a page visually responds to user interactions (taps, clicks, key presses). It reports the worst interaction latency over a visit; a good score is 200 ms or less.Web & SEOLargest Contentful Paint (LCP)Largest Contentful Paint (LCP) is a Core Web Vital that measures how long the largest visible content element (usually a hero image or heading) takes to render. A "good" LCP is 2.5 seconds or less at the 75th percentile.Web & SEOLazy LoadingLazy loading defers loading of off-screen images, iframes, and other resources until the user scrolls near them. It cuts initial page weight and speeds up first render, and is built into browsers via the loading="lazy" attribute.Web & SEOMeta descriptionA meta description is an HTML tag that summarizes a page in roughly 150–160 characters. Search engines often show it as the snippet under the title in results. It is not a direct ranking factor, but a clear, relevant description improves click-through.Web & SEOOpen Graph tagsOpen Graph tags are HTML meta tags (og:title, og:description, og:image, og:url) that control how a page looks when shared on social platforms and chat apps. They set the title, summary, and preview image of the link card instead of leaving it to guesswork.Web & SEOResponsive Images (srcset)Responsive images let the browser pick the best-sized image for each device using the srcset and sizes attributes (or the <picture> element). This avoids sending oversized images to small screens, cutting bandwidth and improving load speed.Web & SEOrobots.txtrobots.txt is a plain-text file at the root of a site (example.com/robots.txt) that tells crawlers which paths they may or may not request. It controls crawling, not indexing — a blocked page can still appear in search if other pages link to it.Web & SEOSoftwareApplication SchemaSoftwareApplication is a Schema.org type that marks up an app's name, category, operating systems, price, and aggregate rating so search engines and AI engines can describe the software and show rich app snippets.Web & SEOStructured data (schema markup)Structured data is machine-readable code, usually written in JSON-LD using the schema.org vocabulary, that labels what a page is about — an article, product, recipe, or FAQ. Search engines use it to understand content and to power rich results like star ratings and FAQ dropdowns.Web & SEOURL slugA URL slug is the readable part of a web address that identifies a specific page — the "what-is-a-url-slug" in example.com/blog/what-is-a-url-slug. A clear, descriptive slug helps users and search engines understand the page before they open it.Web & SEOUTM parametersUTM parameters are tags added to the end of a URL — like ?utm_source=newsletter&utm_medium=email — that tell analytics tools where a visitor came from. They power campaign reporting but do not change the page itself, so they often create duplicate-URL and tracking-clutter issues.Web & SEOWeb Image CompressionWeb image compression reduces an image file's byte size for faster page loads using lossy or lossless encoding, modern formats like WebP and AVIF, correct dimensions, and responsive delivery — without unnecessary loss of visible quality.
Privacy & security 20
Encryption, redaction, permissions, and the networking terms around them.
Privacy & securityAES (Advanced Encryption Standard)AES (Advanced Encryption Standard) is the most widely used symmetric encryption algorithm, adopted as a U.S. government standard and built into nearly every device and app. AES-256 — the 256-bit key version — is the common choice for disk and file encryption.Privacy & securityApp permissionsApp permissions are the approvals an app must request before reaching sensitive data or hardware — photos, contacts, location, camera, microphone. You grant or revoke them per app, and reviewing them is one of the easiest privacy wins.Privacy & securityApp sandboxingApp sandboxing isolates each app in its own restricted container so it can only touch its own files and the data you explicitly allow — not other apps or the rest of the system. It is a core reason phone apps are hard to weaponize against each other.Privacy & securityBandwidthBandwidth is the maximum rate at which data can move over a connection, measured in bits per second (Mbps or Gbps). Higher bandwidth means files transfer faster, but it does not change how much storage those files use once saved.Privacy & securityBiometric authentication (Face ID, fingerprint)Biometric authentication unlocks a device or app using a physical trait — your face or fingerprint — instead of typing a passcode. On phones the biometric data stays in a secure hardware chip and never leaves the device or syncs to the cloud.Privacy & securityCDN (content delivery network)A CDN (content delivery network) is a network of servers spread around the world that store copies of files — images, video, app updates — close to users, so content loads from a nearby server instead of a distant origin. It speeds up downloads without changing how much storage the file uses on your device.Privacy & securityEncryptionEncryption scrambles data into an unreadable form that can only be turned back with a key, so anyone without the key sees noise instead of your files. It is what protects your phone, backups, and messages if a device is lost or intercepted.Privacy & securityHashingHashing turns any input into a fixed-length string of characters using a one-way function — you cannot reverse a hash back into the original data. It is used to store passwords safely, verify files have not changed, and detect duplicates.Privacy & securityMetadata privacy (EXIF/GPS in photos)Photos and files carry hidden metadata — EXIF data including GPS coordinates, the date, and the camera or phone model. Sharing the original file can reveal where a photo was taken, so removing metadata is a key step before posting publicly.Privacy & securityNearby Share / Quick Share (Android)Nearby Share — now branded Quick Share — is Android’s built-in feature for sending photos, files, and links directly between nearby devices, using Bluetooth to pair and Wi-Fi to transfer. It is Android’s equivalent of AirDrop and needs no internet or data plan.Privacy & securityOffline modeOffline mode lets an app work without an internet connection by caching content locally on your device first. Music, maps, videos, and cloud files saved for offline use take up real storage, which is why offline downloads are a common source of a full device.Privacy & securityPeer-to-peer (P2P) transferA peer-to-peer (P2P) transfer moves files directly between two devices without routing them through a central server or the cloud. AirDrop and Quick Share are examples — the connection is device-to-device, so it is fast, private, and works without internet.Privacy & securityPII (personally identifiable information)PII (personally identifiable information) is any data that can identify a specific person — name, email, phone number, address, ID numbers, or even a photo’s location. Knowing what counts as PII helps you redact it before sharing files or screenshots.Privacy & securityProxy serverA proxy server is an intermediary that forwards your web requests on your behalf, so sites see the proxy’s address instead of yours. Unlike a VPN, a basic proxy usually covers only one app or browser and does not encrypt all of your device’s traffic.Privacy & securitySecure deletion (file shredding)Secure deletion permanently erases data so it cannot be recovered, unlike a normal delete that only removes the file’s entry and leaves the contents on disk until overwritten. On modern phones this is done instantly by wiping the encryption key.Privacy & securityTethering / hotspotTethering shares your phone’s cellular connection with another device, turning the phone into a mobile hotspot over Wi-Fi, Bluetooth, or USB. Any data the connected device uses counts against your phone’s cellular allowance.Privacy & securityTwo-factor authentication (2FA)Two-factor authentication (2FA) requires a second proof of identity beyond your password — usually a code from your phone or an app — so a stolen password alone is not enough to sign in. It is one of the strongest, simplest defenses for any account.Privacy & securityUpload vs download speedDownload speed is how fast data comes to your device; upload speed is how fast it leaves. On most home and mobile plans upload is the slower of the two, which is why backing up photos takes far longer than downloading them.Privacy & securityVPN (virtual private network)A VPN (virtual private network) routes your internet traffic through an encrypted tunnel to a remote server, hiding it from your network and masking your IP address with the server’s. It improves privacy on untrusted Wi-Fi but slightly slows transfers and uses no extra device storage.Privacy & securityWi-Fi vs cellular dataWi-Fi connects through a local wireless network and is typically unmetered, while cellular (mobile) data goes over your carrier and usually counts against a monthly allowance. Large transfers like photo backups and app updates are best left to Wi-Fi to avoid data caps.
Cloud & backup 23
How cloud storage, sync, and backups relate to on-device space.
Cloud & backupCloud storageCloud storage keeps your files on a provider’s servers and syncs them to your devices over the internet — iCloud, Google Drive, OneDrive, and Dropbox are the common services. It is separate from a device’s built-in storage, so moving files to the cloud can free local space, but only if local copies are removed.Cloud & backupCloud syncCloud sync keeps a folder of files identical across your devices and an online account, so a change in one place appears everywhere. By default synced files usually exist both in the cloud and on each device, so syncing does not automatically save local space.Cloud & backupDelta sync (block-level)Delta sync (block-level sync) uploads only the parts of a file that changed instead of the whole file. When you edit a large document, the service sends just the modified blocks, which makes syncing big files far faster and lighter on bandwidth.Cloud & backupDevice backupA device backup is a copy of your data — apps, settings, messages, and media — saved to the cloud or a computer so you can restore it after a reset, loss, or new device. A backup is a copy, not freed space: it never reduces the storage used on the device itself.Cloud & backupDifferential backupA differential backup saves everything that changed since the last full backup. Each differential grows over time because it always references the full backup, but restoring is simple: you only need the full backup plus the most recent differential.Cloud & backupDropboxDropbox is a cloud storage service that syncs files across your devices. With Selective Sync and online-only files, items can live in the cloud without using local disk space — they download on demand when you open them.Cloud & backupEnd-to-end encryptionEnd-to-end encryption (E2EE) scrambles data so only your devices hold the keys to read it — not even the service storing it can. It protects messages, backups, and cloud files, but means a lost key can make data unrecoverable.Cloud & backupFile versioning (version history)File versioning keeps older copies of a file each time you save changes, so you can restore a previous version or recover from a bad edit. Cloud services store these versions on their servers, usually without using extra space on your own device.Cloud & backupGoogle DriveGoogle Drive is Google’s cloud storage for files and folders. On desktop, Drive for desktop can stream files (kept online-only and downloaded on demand) or mirror them (a full local copy), which determines how much disk space it uses.Cloud & backupiCloudiCloud is Apple’s cloud service for storing photos, files, backups, and app data across your devices. Every Apple ID gets 5 GB free; paid iCloud+ tiers add more. iCloud storage is separate from the physical storage on your iPhone.Cloud & backupiCloud BackupiCloud Backup is an automatic copy of your iPhone or iPad — app data, settings, Home Screen layout, and Messages — stored in iCloud so you can restore to a new or reset device. It counts against your iCloud storage and is separate from iCloud Photos sync.Cloud & backupiCloud DriveiCloud Drive is Apple’s file-storage and syncing service, accessed through the Files app, that keeps documents and folders available across your devices. Files stored there count against your iCloud storage, and can be kept local or downloaded on demand.Cloud & backupiCloud PhotosiCloud Photos keeps your entire photo and video library in sync across your Apple devices and stores it in iCloud. Because it syncs rather than backs up, a photo you delete on one device is removed everywhere, and the originals count against your iCloud storage.Cloud & backupiCloud+iCloud+ is Apple’s paid subscription that expands iCloud storage beyond the free 5 GB and adds privacy features like Private Relay, Hide My Email, and HomeKit Secure Video. It increases your cloud quota only — it does not add physical storage to your iPhone.Cloud & backupIncremental backupAn incremental backup saves only what changed since the previous backup — full or incremental. Each run is small and fast, but restoring requires the full backup plus every incremental in the chain, in order.Cloud & backupLocal vs cloud storageLocal storage is the fixed physical space inside your device that holds files even offline. Cloud storage is online space on a provider’s servers that you reach over the internet. They are separate pools — adding cloud storage does not enlarge the device, and a full device can coexist with an empty cloud.Cloud & backupMessages in iCloudMessages in iCloud stores your entire iMessage and SMS history — including photos and attachments — in iCloud and keeps it in sync across your devices. It can free device space by offloading old attachments, but the data then counts against your iCloud storage.Cloud & backupMetadata removalMetadata removal is stripping the hidden data embedded in a photo — such as EXIF details, GPS location, and device info — before you share or upload it, so you don’t reveal where or how it was taken.Cloud & backupNAS (network-attached storage)A NAS is a small storage appliance with its own drives that connects to your home or office network, so every device can read and write files to it over Wi-Fi or Ethernet. It acts like a private cloud you own — useful for backups, media, and offloading photos from a full phone.Cloud & backupOneDriveOneDrive is Microsoft’s cloud storage, built into Windows and Microsoft 365. Its Files On-Demand feature keeps files online-only by default, showing them in File Explorer while they use little local disk space until you open them.Cloud & backupOnline-only files (placeholders)Online-only files (placeholders) show every cloud file on your device but store its contents in the cloud until you open it. The file appears in your folders and takes almost no disk space; it downloads on demand and can be made online-only again to reclaim space.Cloud & backupSelective syncSelective sync lets you choose which cloud folders are downloaded to a device, leaving the rest in the cloud only. It is a direct way to free local disk space: unselected folders stay safely online and are not stored on the machine.Cloud & backupSync conflictA sync conflict happens when the same file is changed in two places before the cloud can reconcile them — for example, edited offline on two devices. Rather than lose work, the service keeps both versions, often saving the extra one as a "conflicted copy".
Android development 38
The Android storage, cache, and memory APIs behind how apps use and free space.
Android development.thumbnails FolderThe .thumbnails folder is a hidden cache Android's media layer creates (typically under DCIM/.thumbnails) to store small preview images so galleries load fast. It can grow large over time and is safe to delete because Android rebuilds it on demand.Android development/data/data/data/data is the directory on Android internal storage where each app keeps its private files, databases, shared preferences, and cache. Every package gets its own subfolder, isolated by a unique Linux UID, and the whole folder is deleted when the app is uninstalled.Android developmentallocateBytes() / getAllocatableBytes()Android StorageManager APIs that report and reserve free space. getAllocatableBytes() returns bytes an app could obtain (including space the system can reclaim from clearable caches), and allocateBytes() asks the OS to free that space before you write a large file.Android developmentApp Data vs App CacheOn Android, app data is the permanent files an app needs to work (accounts, settings, databases, downloads), while app cache is regenerable temporary files like thumbnails and network responses. Clearing cache is safe and reversible; clearing data resets the app to a fresh-install state.Android developmentApp Standby BucketsApp Standby Buckets are priority tiers Android assigns to apps based on how recently and often they are used, throttling background jobs, alarms, and network for apps in lower buckets to extend battery life.Android developmentART (Android Runtime)ART (Android Runtime) is the managed runtime that executes Android apps, having replaced Dalvik as the default in Android 5.0. It compiles app bytecode ahead of time and at runtime, producing optimized .oat/.art/.vdex files that speed up apps but also consume storage.Android developmentBitmap Memory ManagementBitmap memory management is how Android allocates, caches, and frees decoded images in RAM. A decoded bitmap costs width x height x bytes-per-pixel, so apps downsample, reuse buffers, and evict caches under memory pressure to avoid OutOfMemoryError.Android developmentclearApplicationUserData()An Android ActivityManager method that erases an app's private data: databases, shared preferences, files, and caches under its data directory. It is the API behind the system's 'Clear storage' / 'Clear data' button and resets the app to a freshly installed state.Android developmentContentResolverContentResolver is the Android client object that talks to content providers. Apps use it to query, insert, update, and delete data behind content:// URIs, including the MediaStore, which is how they list and read photos and videos under scoped storage.Android developmentDalvik CacheThe Dalvik cache is where Android stores ahead-of-time compiled, machine-optimized versions of an app's bytecode (.odex/.oat/.art files) so the app launches fast without recompiling. It lives in system-managed storage and is rebuilt automatically if cleared.Android developmentDEX (Dalvik Executable)DEX (Dalvik Executable) is the bytecode format Android apps ship in. Compiled Java/Kotlin classes are packaged into classes.dex files inside the APK, then optimized by the ART runtime into native code at install or runtime.Android developmentDocumentFileDocumentFile is an AndroidX helper class that wraps a Storage Access Framework document tree URI in a File-like API, letting apps list, create, rename, and delete files under a user-granted folder without raw filesystem paths.Android developmentDocumentsProviderDocumentsProvider is the Android base class an app subclasses to expose a tree of documents (files and folders) to other apps through the Storage Access Framework, surfacing them in the system file picker as a browsable source.Android developmentDoze ModeDoze Mode is an Android power-saving state, introduced in Android 6.0, that the system enters when a device is unused, stationary, and on battery. It defers background CPU and network activity into periodic maintenance windows to extend standby battery life.Android developmentEmulated External StorageEmulated external storage is a FUSE/sdcardfs-backed view that exposes a slice of a device's internal flash through the legacy "external storage" API at /storage/emulated/0. There is no physical SD card; it emulates one so apps written for removable media still work.Android developmentFileProviderFileProvider is an Android component that grants other apps temporary, permission-scoped access to your files by handing out a content:// URI instead of a raw file path. It is the standard way to share or open a file safely on modern Android.Android developmentgetCacheDir()getCacheDir() returns the app's private internal cache directory on Android. Files there are app-owned, count as the app's cache in Settings, and the system can auto-delete them under low storage. The OS also wipes them when the app is uninstalled.Android developmentgetExternalCacheDir()getExternalCacheDir() returns an app-private cache directory on external (shared) storage. It needs no permission, counts as the app's cache in Settings, and is deleted on uninstall, but the OS does not guarantee auto-eviction of it under low storage.Android developmentgetExternalFilesDir()An Android Context method returning an app-specific directory on external/shared storage. Files here belong to the app, need no storage permission, and are deleted automatically when the app is uninstalled — but they still count toward the app's storage footprint.Android developmentJetpack DataStoreJetpack DataStore is the modern Android API for storing small amounts of key-value or typed data asynchronously, using Kotlin coroutines and Flow. It is Google's recommended replacement for SharedPreferences.Android developmentJobSchedulerJobScheduler is the Android system service for scheduling deferrable background jobs that run under conditions like charging, idle, or unmetered network, batching work across apps to save battery instead of running immediately.Android developmentLruCache (Android)LruCache is Android's in-memory, fixed-size cache that evicts the least recently used entries when it hits its limit. It's the standard way apps cache decoded bitmaps and other objects in RAM, releasing the oldest items first to stay within a memory budget.Android developmentMANAGE_EXTERNAL_STORAGEMANAGE_EXTERNAL_STORAGE is the Android "All files access" permission that grants an app broad read and write access to most of shared external storage, bypassing scoped storage restrictions. It is a special permission granted only through a system Settings screen, not a runtime dialog, and Google Play strictly gates its use.Android developmentMedia Scanner (MediaScannerConnection)Android's media scanner is the system service that indexes media files into the MediaStore database so they appear in Gallery, Photos, and content queries. Apps trigger it via MediaScannerConnection.scanFile to add or refresh entries after creating or deleting files.Android developmentMediaStore APIMediaStore is Android's system content provider that indexes shared media (images, video, audio, downloads) across the device. Apps query it via ContentResolver to list photos and metadata without raw file access, which is the standard way under scoped storage.Android developmentOBB Expansion Files InternalsOBB (Opaque Binary Blob) expansion files are large asset bundles, mainly game data, stored alongside an Android app outside its APK. They live under Android/obb/<package>/ on shared storage and let titles ship gigabytes of media beyond installer size limits.Android developmentonLowMemory()onLowMemory() is an Android callback the system invokes when the whole device is critically low on memory, signaling running apps to release non-essential resources like caches and bitmaps before processes get killed.Android developmentonTrimMemory()onTrimMemory() is an Android callback the system invokes on Application, Activity, and other ComponentCallbacks2 components to signal memory pressure. A level constant tells the app how urgently it should release memory, such as in-memory caches and bitmaps, to avoid being killed when the device runs low on RAM.Android developmentrequestLegacyExternalStoragerequestLegacyExternalStorage is a manifest flag that let apps temporarily opt out of scoped storage and keep using raw file paths on Android 10. It is ignored on Android 11+, where scoped storage is always enforced.Android developmentRoom Persistence LibraryRoom is an Android Jetpack persistence library that provides a typed abstraction layer over SQLite. It maps annotated entity classes to tables, validates SQL queries at compile time, and exposes results as Flow or LiveData for reactive UIs.Android developmentScoped Storage InternalsScoped storage is the Android storage model, introduced in Android 10 and enforced from Android 11, that limits an app's direct filesystem access to its own package directories and the shared media collections. Other apps' files and arbitrary paths are reached only through MediaStore, the Storage Access Framework, or special permissions.Android developmentSharedPreferencesSharedPreferences is an Android API for storing small amounts of key-value data (settings, flags, tokens) in a private XML file inside the app's data directory, persisted across launches without a database.Android developmentStorage Access FrameworkThe Storage Access Framework (SAF) is an Android system for browsing and accessing files and directories through a document provider model. Apps use intents like ACTION_OPEN_DOCUMENT and ACTION_OPEN_DOCUMENT_TREE to let the user pick files or a whole folder, and receive a persistable URI instead of a raw file path.Android developmentStorage Volumes (Android)On Android, a storage volume is a logical unit of mountable storage such as built-in internal storage or a removable SD card. Apps enumerate them through StorageManager.getStorageVolumes() to discover each volume's path, state, and whether it is the primary or removable volume.Android developmentStorageManager (Android)StorageManager is the Android system service apps use to query storage volumes, request free space, and let the OS reclaim clearable cache. Its allocateBytes and getCacheQuotaBytes APIs help apps make room before writing large files.Android developmentStorageStatsManagerStorageStatsManager is the Android system service (added in API 26) that reports how much storage apps and the device are using, broken into app code, user data, and cache. It is the supported way for a cleaner to read accurate per-app cache and data sizes.Android developmentTrim Memory LevelsTrim memory levels are the TRIM_MEMORY_* constants Android passes to an app's onTrimMemory() callback, signaling how much memory pressure the system is under so the app can release caches, bitmaps, and other reclaimable resources.Android developmentWorkManagerWorkManager is the Android Jetpack library for scheduling deferrable, guaranteed background work that must run even if the app exits or the device reboots. It picks JobScheduler or an internal fallback per OS version, and respects Doze and battery limits.
iOS development 25
The iOS/iPadOS file, cache, and photo APIs that decide what a device stores.
iOS developmentApp Group ContainerAn App Group container is a shared on-disk directory and preferences domain that lets an iOS app, its extensions, and related apps from the same developer read and write the same files outside their individual sandboxes.iOS developmentApp SlicingApp Slicing is the App Store delivery feature that builds and ships a device-specific variant of an app, including only the executable code and resources (textures, images) a given device actually needs, so each download and install is smaller than the universal binary.iOS developmentApp Thinning InternalsApp thinning is the App Store process that delivers only the resources and code a specific device needs, shrinking installed app size. It combines slicing (per-device variants), On-Demand Resources, and historically bitcode-based recompilation.iOS developmentApplication Support DirectoryThe Application Support directory (Library/Application Support) holds an app's persistent support files — databases, configuration, and downloaded resources the app needs to function. Unlike Caches, it is backed up and not purged by the system.iOS developmentBackground URLSessionA Background URLSession is a URLSession configured with background(withIdentifier:) so transfers run in a separate system daemon and continue after the app is suspended or terminated, with the OS relaunching the app on completion.iOS developmentCore Data StoreA Core Data store is the on-disk persistent backing of an app's Core Data object graph, most commonly a SQLite database file. It holds the app's structured data and can grow large over time as records, indexes, and write-ahead logs accumulate.iOS developmentFileManager (iOS)FileManager is the Foundation class iOS apps use to read, create, move, copy, and delete files and directories inside their sandbox. It exposes URLs for system locations (Documents, Caches, tmp) and reports per-file size and dates, so a storage cleaner relies on it to enumerate and remove reclaimable files.iOS developmentiCloud Ubiquitous ItemA ubiquitous item is a file managed by iCloud that may live in the cloud rather than fully on the device. iOS represents it with a local placeholder and downloads the real contents on demand, which is why some files show as not yet downloaded.iOS developmentiOS App Sandbox DirectoriesEvery iOS app runs inside a sandboxed data container with a fixed set of directories: Documents, Library (including Caches and Application Support), and tmp. Each has distinct backup and purge rules that determine whether files persist, get backed up to iCloud, or are deleted by the system to reclaim space.iOS developmentisExcludedFromBackupisExcludedFromBackup is a per-file URL resource key on iOS that marks a file or folder so iCloud and iTunes/Finder backups skip it, keeping regenerable caches and downloads out of the user's backup.iOS developmentNSCacheNSCache is a mutable, thread-safe in-memory key-value cache in Apple's Foundation framework that automatically evicts its objects when the system comes under memory pressure, making it the recommended store for transient data like decoded images and computed results.iOS developmentNSCachesDirectoryNSCachesDirectory is the search-path constant for an iOS app's Library/Caches folder, where apps store regenerable data like downloaded images and computed files. Its contents are purgeable: iOS can delete them under low-storage pressure, and they are excluded from iCloud and iTunes backups.iOS developmentNSFileProtectionNSFileProtection is iOS's Data Protection API that assigns each file an encryption class controlling when its contents are readable, typically tied to whether the device is unlocked, so files stay encrypted at rest until the right key is available.iOS developmentNSPurgeableDataNSPurgeableData is a Foundation subclass of NSMutableData whose backing memory the system can automatically discard under memory pressure. You bracket access with beginContentAccess and endContentAccess so iOS knows when the bytes are safe to reclaim.iOS developmentOn-Demand Resources InternalsOn-Demand Resources (ODR) let an iOS app download tagged asset packs from the App Store after install and have the OS purge them automatically under storage pressure. The downloaded content counts as purgeable space the system can reclaim without uninstalling the app.iOS developmentPHAssetPHAsset is the PhotoKit object that represents a single photo, video, or Live Photo in the iOS Photos library. It carries metadata such as capture date, dimensions, and media type, but holds no pixel data itself; the actual image is loaded on demand through PHImageManager using the asset's identifier.iOS developmentPHAssetResourcePHAssetResource describes the underlying files that back a PHAsset, such as the full-size photo, an edited version, an adjustment sidecar, or a paired video for a Live Photo. It is how iOS apps inspect resource types and read original file data.iOS developmentPHImageManagerPHImageManager is the PhotoKit class that loads images and videos for PHAsset objects, returning cached thumbnails or full-resolution data on demand. It handles downloading from iCloud, scaling, and request cancellation so apps never touch raw photo files directly.iOS developmentPhoto Deletion Flow (PhotoKit)On iOS, apps delete photos through PhotoKit by wrapping PHAssetChangeRequest.deleteAssets in PHPhotoLibrary.performChanges. iOS shows a system confirmation the user must approve, and the photos move to Recently Deleted for ~30 days rather than being erased immediately.iOS developmentPhotoKitPhotoKit is Apple's framework for reading and managing a user's Photos library on iOS and iPadOS. It exposes the library through the Photos and PhotosUI modules, letting an app fetch photos and videos, load image data, and request edits or deletions through a permission-gated, change-aware API.iOS developmentPurgeable Space InternalsPurgeable space is storage iOS counts as in-use but can automatically reclaim when the disk fills. It is made of caches, temporary files, and offloadable content the system can regenerate or re-download, so free space and purgeable space together form the true headroom available for new data.iOS developmenttemporaryDirectory (iOS)temporaryDirectory is the per-app tmp folder where iOS apps write short-lived working files. It is unique to the app sandbox, excluded from backups, and may be emptied by the system when the app is not running, making it a natural target for both system and in-app cleanup.iOS developmentURLCacheURLCache is Foundation's in-memory and on-disk cache for HTTP and HTTPS responses fetched via URLSession. It stores response data keyed by request so repeat network calls can be served locally. Apps can inspect its current size and clear it, which a storage cleaner uses to reclaim network cache.iOS developmentURLSession Cache PolicyURLSession cache policy controls whether an iOS network request reuses a stored HTTP response or revalidates with the server. It is set via URLRequest.cachePolicy and backed by URLCache, which holds responses in memory and on disk.iOS developmentUserDefaultsUserDefaults is Apple's lightweight key-value store for persisting small pieces of user preference and app configuration data, backed by a property list (.plist) file in the app container. It is meant for settings, not bulk data or caches.
APIs & internals 44
File systems, memory, and cross-platform internals that explain where space goes.
APIs & internalsaHashaHash (average hash) is a perceptual image hashing algorithm that fingerprints a photo by comparing each pixel of a tiny grayscale thumbnail to the image's average brightness. Similar images produce similar hashes, so near-duplicates can be matched even after resizing or recompression.APIs & internalsAPFS ClonesAPFS clones are copy-on-write file copies in Apple File System: cloning a file creates a new directory entry that shares the original's data blocks, so the copy uses almost no extra space until one side is modified.APIs & internalsAPFS InternalsAPFS (Apple File System) is the default file system on iOS, iPadOS, and macOS. It uses copy-on-write metadata, space-sharing containers, snapshots, and clones to manage storage, which is why iPhone and Mac free space can shift even when you haven't added or deleted obvious files.APIs & internalsAPFS SnapshotsAn APFS snapshot is a read-only, point-in-time image of a volume that records its exact state at a moment. Snapshots share data blocks with the live volume, so they cost little at first but grow as files change, often appearing as hidden System Data that fills storage on iPhone and Mac.APIs & internalsAPFS Space SharingAPFS space sharing lets multiple volumes inside one APFS container draw from a single shared pool of free space, so each volume's free space reflects the whole container rather than a fixed partition size. This is why free space on Apple devices can look inconsistent.APIs & internalsBlock SizeBlock size is the smallest unit of space a filesystem allocates to a file. Because files are rounded up to whole blocks, a file smaller than one block still consumes a full block, which is why many tiny files use more disk space than their byte sizes suggest.APIs & internalsBlock-Level DeduplicationBlock-level deduplication splits data into fixed or variable-sized blocks, fingerprints each one, and stores only a single physical copy of any block that repeats. References point back to that copy, so identical data across many files consumes space just once.APIs & internalsCopy-on-WriteCopy-on-write (CoW) is a storage technique where a copy shares the original's data blocks until something changes; only modified blocks are written to new locations, so copies are cheap and changes never overwrite shared data in place.APIs & internalsCRC32CRC32 is a 32-bit cyclic redundancy check that produces a short checksum of a file or data block to detect accidental corruption. It is fast and widely used in formats like ZIP and PNG, but it is an error-detection code, not a secure or cryptographic hash.APIs & internalsdHashdHash (difference hash) is a fast perceptual hashing algorithm that fingerprints an image by comparing the brightness of adjacent pixels. Each bit records whether one pixel is brighter than its neighbor, producing a compact 64-bit hash that stays stable across resizes and re-compression.APIs & internalsDisk Cache vs Memory CacheA memory cache stores data in RAM for fast, volatile reuse within a running app, while a disk cache persists data to storage so it survives app restarts. Most apps layer both: a small fast memory tier in front of a larger persistent disk tier.APIs & internalsext4 File Systemext4 (fourth extended filesystem) is a widely used Linux journaling file system found on many Android devices' data partitions. It uses extents, delayed allocation, and a journal to store files reliably, and understanding it explains why Android storage fills up and how cleanup reclaims space.APIs & internalsF2FS File SystemF2FS (Flash-Friendly File System) is a Linux file system designed specifically for flash storage like the eMMC and UFS chips in phones. Many Android devices use it on the data partition because its log-structured, flash-aware design improves speed and longevity, and it shapes how Android storage fills and frees.APIs & internalsFile-Level DeduplicationFile-level deduplication treats each whole file as the unit: it fingerprints entire files and keeps only one copy of any that are identical. Also called single-instance storage, it is simpler than block-level dedup but only catches files that match in full.APIs & internalsFilesystem JournalingFilesystem journaling records pending changes in a dedicated log before applying them to the main filesystem. After a crash or power loss, the journal is replayed or discarded so the filesystem stays consistent instead of corrupted.APIs & internalsFragmentationFragmentation is when the data for a single file is scattered across non-contiguous physical locations on a storage device, instead of sitting in one continuous run. It builds up as files are repeatedly created, grown, and deleted, leaving a patchwork of free gaps.APIs & internalsHamming DistanceHamming distance is the number of positions at which two equal-length bit strings differ. For image hashes, it counts how many bits two fingerprints disagree on, giving a simple, fast similarity score: a small distance means the images look alike, a large distance means they do not.APIs & internalsHard LinkA hard link is an additional directory entry pointing to the same inode as an existing file. Multiple hard links are equally valid names for one set of data, and the file's blocks are freed only when the last link is removed.APIs & internalsInode InternalsAn inode is the on-disk data structure that stores a file's metadata and pointers to its data blocks, but not its name or contents. The filesystem uses inodes to map a file to the actual storage blocks it occupies.APIs & internalsLocality-Sensitive HashingLocality-Sensitive Hashing (LSH) is a technique that hashes similar items into the same buckets with high probability, so near-duplicate search scales without comparing every pair. It turns an O(n^2) all-pairs problem into a fast bucket lookup over huge collections.APIs & internalsLRU Cache EvictionLRU (Least Recently Used) eviction is a cache policy that discards the entries accessed longest ago when the cache hits its size limit, keeping hot data and dropping cold data first. It is the default strategy behind many in-app memory and disk caches.APIs & internalsMD5 ChecksumAn MD5 checksum is a 128-bit value computed from a file's exact bytes. Two byte-identical files always produce the same MD5, while changing a single byte produces a completely different value, making it a fast way to detect exact-duplicate files.APIs & internalsMemory-Mapped FileA memory-mapped file maps a file's contents directly into a process's virtual address space, so the OS pages data in on demand instead of copying it with explicit read/write calls. It lets apps treat a large file like an in-memory array.APIs & internalsPage CacheThe page cache is the operating system's in-RAM copy of recently read or written file data. It lets repeat file access hit memory instead of slow storage, and it is reclaimed automatically the moment apps need RAM — so it is not 'used up' memory or app cache.APIs & internalsPerceptual HashA perceptual hash (pHash) is a compact fingerprint, usually a 64-bit value, computed from an image's visual structure rather than its raw bytes. Unlike cryptographic hashes, two images that look alike produce similar hashes, so small edits, resizes, or re-compressions change only a few bits.APIs & internalspHash (DCT Hash)pHash (DCT hash) is a perceptual image hashing method that applies a Discrete Cosine Transform to a grayscale thumbnail and keeps the low-frequency coefficients. This makes its fingerprint robust to scaling, recompression, and many edits, so visually similar photos hash alike.APIs & internalsRaw vs Usable CapacityRaw capacity is the total flash a device physically contains; usable capacity is what you can actually store after the OS, file-system overhead, reserved blocks, and decimal-vs-binary counting are subtracted. That gap is why a "128 GB" phone shows noticeably less free space.APIs & internalsSHA-256 ChecksumA SHA-256 checksum is a 256-bit (32-byte) fingerprint produced by the SHA-2 hash function. Running it over a file's bytes yields a fixed 64-character hex string that changes completely if any byte changes, so two files with the same SHA-256 are byte-for-byte identical in practice.APIs & internalsSlack SpaceSlack space is the unused remainder inside the last block a file occupies, left over because filesystems allocate whole blocks. It is space reserved by a file but not filled with its data, and it accumulates across many small files.APIs & internalsSparse FileA sparse file is a file whose empty (all-zero) regions, called holes, are not actually stored on disk. It reports a large logical size but consumes far fewer real blocks, so its apparent size and on-disk size differ.APIs & internalsSQLite Auto-VacuumSQLite Auto-Vacuum automatically reclaims space from deleted rows by shrinking the database file, instead of leaving free pages that bloat it. It helps keep app databases from growing unnecessarily over time.APIs & internalsSQLite VACUUMVACUUM is a SQLite command that rebuilds a database file from scratch, repacking pages to remove free space left by deletions and updates. It shrinks the file on disk, defragments it, and can reduce fragmentation, but requires extra temporary space to run.APIs & internalsSQLite WAL ModeSQLite WAL (Write-Ahead Logging) mode records database changes in a separate -wal file before merging them into the main database, improving concurrency and crash safety. It explains the -wal and -shm files cleaners often see.APIs & internalsSwap SpaceSwap space is storage set aside as overflow for RAM: when physical memory fills up, the OS writes idle memory pages to a swap file or partition and reloads them on demand. It lets a system keep running under memory pressure at the cost of slower disk access.APIs & internalsSymbolic LinkA symbolic link (symlink) is a small special file that stores a path to another file or directory. It resolves to its target at access time, can cross filesystems, and becomes a dangling link if the target is removed.APIs & internalstmpfstmpfs is a file system that lives in RAM (and swap) instead of on disk. Files written to it are fast and never touch flash storage, but they vanish on reboot — making it ideal for temporary scratch data that should not consume permanent storage.APIs & internalsTRIM vs DiscardTRIM and discard are two names for the same idea: telling flash storage which blocks a deleted file no longer needs, so the controller can erase them ahead of time. 'TRIM' is the SATA/SSD command name; 'discard' is the generic file-system/Linux term that also covers UNMAP on UFS/eMMC.APIs & internalsVirtual MemoryVirtual memory is an abstraction that gives each process its own private address space, which the OS maps to physical RAM (and sometimes disk) in fixed-size pages. It isolates processes and lets the system run programs that need more memory than is physically installed.APIs & internalsWear LevelingWear leveling is a flash-memory technique that spreads write and erase operations evenly across all storage cells so no single block wears out early. It runs inside the storage controller and is invisible to apps and the file system.APIs & internalswHash (Wavelet Hash)Wavelet hash (wHash) is a perceptual image-hashing method that uses a discrete wavelet transform to produce a compact fingerprint of an image. Visually similar photos get near-identical hashes, making it useful for finding duplicate and similar images.APIs & internalsWrite AmplificationWrite amplification is the ratio of physical data actually written to flash versus the logical data the host requested. Because flash erases in large blocks but writes in small pages, a single app write can trigger several times more internal writes.APIs & internalsxxHashxxHash is an extremely fast non-cryptographic hash function used to fingerprint files and data blocks. It runs at memory-bandwidth speeds, making it ideal for deduplication, integrity checks, and hash tables where speed matters more than collision resistance against attackers.APIs & internalsZFSZFS is a copy-on-write file system and volume manager known for end-to-end checksums, snapshots, and built-in block-level deduplication. It pools storage devices together and verifies data integrity on every read.APIs & internalszRAMzRAM is a Linux kernel feature, used widely on Android, that creates a compressed block device in RAM and uses it as swap. Idle memory pages are compressed in place rather than written to flash, easing memory pressure without touching your file storage.
Build & packaging 27
How apps are packaged, signed, and installed — APKs, app bundles, and IPAs.
Build & packagingAndroid App Bundle (AAB)An Android App Bundle (.aab) is the publishing format developers upload to Google Play. Play uses it to generate and sign optimized APKs tailored to each device, so users download only the code and resources their phone actually needs.Build & packagingAndroid App LinksAndroid App Links are HTTP(S) deep links that Android verifies against a website you own, so tapping a matching URL opens your app directly instead of showing a chooser or the browser. Verification uses a Digital Asset Links JSON file hosted on your domain.Build & packagingAndroid App SigningAndroid app signing attaches a developer's cryptographic signature to an APK so the system can verify the package's author and confirm it has not been modified. Android also requires that app updates be signed with the same key as the installed version.Build & packagingAndroid IPC (Binder)Binder is Android's core inter-process communication (IPC) mechanism—a kernel driver and userspace framework that lets an app's process call methods in system services like the media store across process boundaries.Build & packagingAndroidManifest.xmlAndroidManifest.xml is the required configuration file at the root of every Android app that declares its package identity, components, hardware features, and the permissions it requests, including storage and media access. The OS reads it before any code runs.Build & packagingAPK File InternalsAn APK is a ZIP archive holding everything Android needs to install an app: compiled DEX bytecode, the AndroidManifest, resources and assets, native libraries, and a signing block. Its size, plus extracted runtime caches, is what shows up as installed app size.Build & packagingApp SandboxAn app sandbox is an OS-enforced isolation boundary that confines each app to its own private files, memory, and limited system resources, so one app cannot read or modify another app's data without explicit, mediated permission.Build & packagingApp Uninstall LeftoversApp uninstall leftovers are files an app leaves behind after you remove it: documents, media, logs, or data it wrote to shared storage. Because they are no longer owned by any installed app, these orphaned files take up space without serving any purpose.Build & packagingBackground Execution LimitsBackground execution limits are Android restrictions that stop apps from running freely once they leave the foreground. The system curbs background services, throttles work via Doze and App Standby, and can place idle apps in restricted buckets, pausing long-running tasks.Build & packagingBackground Tasks (iOS)iOS Background Tasks are system-scheduled windows, managed by the BackgroundTasks framework, in which an app can run short maintenance or longer processing work while it is not on screen. iOS decides when they run based on usage, battery, and charging state.Build & packagingContent Provider InternalsA content provider is an Android component that exposes a structured, permission-controlled data set through content:// URIs, letting one app query, insert, update, or delete another app's data via a ContentResolver. MediaStore is the system provider for photos, videos, and audio.Build & packagingDeep LinkA deep link is a URL that opens a specific screen inside an app rather than its home screen—for example a link that jumps straight to a cleanup or duplicate-photos view. Verified web-domain deep links are called Universal Links (iOS) and App Links (Android).Build & packagingEntitlements (iOS)Entitlements are key-value capabilities embedded in an iOS app's code signature that grant access to protected system features — such as iCloud, push notifications, App Groups, or HealthKit. They are declared at build time and enforced by the OS at runtime.Build & packagingForeground ServiceAn Android foreground service is a long-running service the user is actively aware of, shown with a persistent status-bar notification. It keeps work like a storage scan alive after the user leaves the app, with a far lower chance of being killed than a background service.Build & packagingInfo.plistInfo.plist is the required property-list manifest in every iOS, iPadOS, and macOS app bundle. It declares core metadata — bundle identifier, version, supported devices — plus the usage-description strings that gate access to the photo library, camera, and other protected data.Build & packagingIntents (Android)An Intent is Android's messaging object for requesting an action—launching an activity, sharing a file, or starting a service. Explicit intents name a target component; implicit intents describe an action the system resolves to a matching app.Build & packagingiOS Code SigningiOS code signing cryptographically seals an app with a developer certificate and a provisioning profile so iOS and the App Store can verify its origin and integrity. Unsigned or tampered apps will not launch on a device.Build & packagingIPA File InternalsAn IPA (.ipa) is the iOS/iPadOS app archive Apple distributes through the App Store. It is a ZIP container holding a signed `.app` bundle with the compiled binary, resources, Info.plist, and embedded provisioning and entitlement data.Build & packagingLimited Photo Library AccessLimited Photo Library Access is an iOS and iPadOS privacy option that lets you grant an app access to only a hand-picked selection of photos instead of your whole library. The app can see and act on the chosen images only, so anything you did not select stays hidden from it.Build & packagingOrphaned FilesOrphaned files are data left on storage that no app, database, or index still references, such as leftovers from a deleted or updated app, an interrupted download, or a stale cache. They occupy space without serving any current purpose and are usually safe to remove.Build & packagingPhoto Library PermissionPhoto Library Permission is the iOS and iPadOS consent an app must obtain before it can read or modify the system Photos library through PhotoKit. The user chooses Full Access, Limited (a selected subset), or None. A cleaner needs this grant to scan your photos for duplicates and clutter, and the choice controls what it can see.Build & packagingProvisioning ProfileA provisioning profile is a signed Apple file that ties an app's bundle ID, signing certificate, entitlements, and (for development) allowed device UDIDs together, authorizing that build to install and run on iOS/iPadOS.Build & packagingREAD_MEDIA_IMAGES / VIDEOREAD_MEDIA_IMAGES and READ_MEDIA_VIDEO are granular Android runtime permissions introduced in Android 13 (API 33) that replace the broad READ_EXTERNAL_STORAGE for media. They let an app read only photos or only videos, instead of all shared storage. A cleaner requests them to scan your camera roll for duplicates and clutter.Build & packagingRuntime Permissions (Android)Runtime permissions are dangerous-level Android permissions that an app must request from the user while it is running, not just declare in its manifest. Introduced in Android 6.0 (API 23), they show a system dialog the user can grant or deny. A storage cleaner uses them to ask for access to your photos and media before it can scan them.Build & packagingSplit APKsSplit APKs break an Android app into a base APK plus separate configuration APKs for each device's CPU architecture, screen density, and language. Google Play installs only the pieces a given device needs, so less is downloaded and stored.Build & packagingStorage Permission Changes by API LevelAndroid's storage permission model has shifted across API levels from broad READ/WRITE_EXTERNAL_STORAGE to scoped storage, granular media permissions, and the Photo Picker. Each change narrowed what an app can read or delete, which is why cleanup behavior differs by OS version.Build & packagingUniversal LinksUniversal Links are standard https URLs that open an installed iOS/iPadOS app directly instead of Safari, after the system verifies domain ownership via an apple-app-site-association file. If the app isn't installed, the same link loads the web page.
A–Z index
Every term in the reference, alphabetically.
#
A
- AAB (Android App Bundle)
- AAC
- ABC (Alembic)
- AC-3 (Dolby Digital)
- ACCDB (Access)
- ACE
- Adaptive bitrate streaming (HLS)
- Adoptable storage
- AES (Advanced Encryption Standard)
- aHash
- AI (Adobe Illustrator)
- AIFC (compressed AIFF)
- AIFF
- AirDrop
- ALAC (Apple Lossless)
- allocateBytes() / getAllocatableBytes()
- Allocation unit (cluster size)
- Alpha channel (transparency)
- Alt text
- AMR
- Android App Bundle (AAB)
- Android App Links
- Android App Signing
- Android IPC (Binder)
- Android/data folder
- AndroidManifest.xml
- Animated WebP
- APE (Monkey’s Audio)
- APFS
- APFS Clones
- APFS Internals
- APFS local snapshot
- APFS Snapshots
- APFS Space Sharing
- APK (Android app package)
- APK File Internals
- APNG
- App cache
- App Clips
- App Data vs App Cache
- App Group Container
- App Library
- App permissions
- App Sandbox
- App sandboxing
- App Slicing
- App Standby Buckets
- App thinning
- App Thinning Internals
- App Uninstall Leftovers
- AppData folder (Windows)
- Apple ProRAW
- Application Support Directory
- Archive file
- ARJ
- ART (Android Runtime)
- ARW (Sony RAW)
- Aspect ratio
- ASS / SSA subtitles
- AU / SND (Sun audio)
- Autofill data
- AV1 vs HEVC
- AVI
- AVIF
- Avro
- AZW3 (Kindle)
B
- Background Execution Limits
- Background removal
- Background Tasks (iOS)
- Background URLSession
- Bad sector
- BAK (backup) file
- Bandwidth
- Base64 encoding
- Batch image resizing
- BDF (bitmap font)
- BIN file (.bin)
- BIN/CUE
- Biometric authentication (Face ID, fingerprint)
- Bit depth
- Bitmap Memory Management
- Bitrate
- Bitrate mode (CBR vs VBR)
- Bitrate vs Resolution
- BLEND (Blender)
- Bloatware
- Block Size
- Block-Level Deduplication
- BMP
- Books & PDF storage
- Brotli (.br)
- Browser cache
- Browsing history
- Burst Photo Storage
- Burst photos
- BZIP2 (.bz2)
C
- C4D (Cinema 4D)
- CAB (Windows cabinet)
- Cache Partition
- Cached Data
- CAF (Core Audio Format)
- Camera RAW (CR2, NEF, ARW)
- Canonical tag
- CBR
- CBT (comic TAR)
- CBZ
- CDN (content delivery network)
- CDR (CorelDRAW)
- Chroma subsampling (4:2:0)
- Chroma Subsampling 4:2:0 vs 4:4:4
- Clear Data vs Clear Cache
- clearApplicationUserData()
- Cloud storage
- Cloud sync
- Codec
- Color banding
- Color gamut
- Color grading
- Color Profile (ICC)
- Color quantization
- Color space (sRGB, CMYK)
- Compression (lossy vs lossless)
- Constant Rate Factor (CRF)
- Container format
- Container vs Codec
- Content Provider Internals
- ContentResolver
- Cookies
- Copy-on-Write
- Core Data Store
- Core Web Vitals
- CPIO
- CR2 (Canon RAW)
- CR3 (Canon RAW)
- CRC32
- CSS
- CSV
- Cumulative Layout Shift (CLS)
D
- DAE (COLLADA)
- Dalvik Cache
- Dalvik/ART cache
- DAT file (.dat)
- Data units (KB, MB, GB, TB)
- DBF (dBASE)
- DCI-P3
- DDS (DirectDraw Surface)
- DEB (Debian package)
- Deep Link
- DefinedTerm Schema
- Delivery Optimization files
- Delta sync (block-level)
- Device backup
- Device Care
- DEX (Dalvik Executable)
- dfont (Mac font)
- dHash
- Differential backup
- Digital signature
- DirectX shader cache
- Disk Cache vs Memory Cache
- Disk Cleanup
- Disk image
- Disk partition
- DivX
- DjVu
- DMG (Apple disk image)
- DNG (digital negative)
- Dockerfile
- DocumentFile
- Documents & Data
- DocumentsProvider
- DOCX (Word)
- Downloaded Media Cache
- Downloads folder
- Downloads folder (Mac)
- Doze Mode
- DPI vs PPI
- DRC (Draco 3D)
- Dropbox
- DSD
- DTS (Digital Theater Systems)
- Duplicate photos
- DV (Digital Video)
- DVI
- DWG (AutoCAD drawing)
- DXF (CAD exchange)
E
F
- F2FS File System
- F4V (Flash MP4)
- Family Sharing
- FAQPage Schema
- FAT32
- Favicon
- FB2
- FBX (3D)
- Featured Snippet
- File format conversion
- File system
- File versioning (version history)
- File-Level Deduplication
- FileManager (iOS)
- FileProvider
- Files by Google
- Filesystem Journaling
- Fillable PDF form
- Find My
- FLAC
- Flash storage
- FLV (Flash video)
- FON (bitmap font)
- Foreground Service
- Formatted capacity (why 128GB shows less)
- Fragmentation
- Frame rate (fps)
G
H
I
- iCalendar (.ics)
- iCloud
- iCloud Backup
- iCloud Drive
- iCloud Keychain
- iCloud Photos
- iCloud Ubiquitous Item
- iCloud+
- ICNS (Mac icon)
- ICO (icon file)
- IFO (DVD info)
- Image CDN
- Image compression
- Image cropping
- Image Downsampling
- Image Pyramid
- Image redaction
- Image resolution
- Image to PDF
- Image upscaling
- Incremental backup
- INDD (Adobe InDesign)
- IndexedDB
- Info.plist
- INI file
- Inode
- Inode Internals
- Intents (Android)
- Interaction to Next Paint (INP)
- Interframe compression
- Interlacing vs progressive
- Internal storage
- Internal vs external storage
- Intra vs Inter Frame
- iOS App Sandbox Directories
- iOS Code Signing
- iOS Update Space
- IPA (iOS app archive)
- IPA File Internals
- IPTC Metadata
- isExcludedFromBackup
- ISO (disk image)
- IT (Impulse Tracker)
J
L
- Large Files
- Largest Contentful Paint (LCP)
- Lazy Loading
- Leftover APK Files
- Letterboxing & pillarboxing
- Limited Photo Library Access
- LIT (Microsoft Reader)
- Live Photo
- Live Photo Storage Anatomy
- Local storage (localStorage)
- Local vs cloud storage
- Locality-Sensitive Hashing
- LOG file (.log)
- Lossy vs Lossless Compression
- Low Storage Warning
- LRU Cache Eviction
- LruCache (Android)
- LWO (LightWave)
- LZ4
- LZH / LHA
M
- M2TS (Blu-ray)
- M2V (MPEG-2 video)
- M4A
- M4B (audiobook)
- M4P (protected AAC)
- M4R (iPhone ringtone)
- M4V
- MA/MB (Maya)
- Mail Storage
- MANAGE_EXTERNAL_STORAGE
- Markdown
- MBR vs GPT
- MD5 Checksum
- MDB (Access)
- MDF/MDS (disc image)
- Media Scanner (MediaScannerConnection)
- MediaStore API
- Megapixel
- Memory card (SD/microSD)
- Memory-Mapped File
- Messages in iCloud
- Messaging App Storage
- Meta description
- Metadata privacy (EXIF/GPS in photos)
- Metadata removal
- microSD card
- MIDI
- MKA (Matroska Audio)
- MKV
- MNG (animated PNG predecessor)
- MOBI (Kindle ebook)
- Mobile Browser Cache
- MOD (tracker module)
- Motion Compensation
- MOV
- MP3
- MP4
- MPEG (.mpg)
- MPP (Project)
- MSI (Windows installer)
- MSIX (Windows app)
- MTS / AVCHD
- Musepack (.mpc)
- MXF (broadcast)
N
O
- OBB Expansion Files Internals
- OBB files
- OBJ (3D model)
- OCR (optical character recognition)
- ODP (OpenDocument Presentation)
- ODS (OpenDocument Spreadsheet)
- ODT (OpenDocument Text)
- Offline Map Cache
- Offline mode
- Offload App
- OGA (Ogg audio)
- Ogg
- OGV (Ogg video)
- On-Demand Resources
- On-Demand Resources Internals
- ONE (OneNote)
- OneDrive
- Online-only files (placeholders)
- onLowMemory()
- onTrimMemory()
- Open Graph tags
- OPF (ebook package)
- Optimize iPhone Storage
- Opus
- ORF (Olympus RAW)
- Orphaned Files
- OTF (OpenType font)
- Other / Misc storage
P
- Page Cache
- Pagefile (pagefile.sys)
- Pages (Apple)
- Panorama
- Parquet
- PBM
- PCM
- PCX
- PDB (Palm/ebook)
- PDF compression
- PDF encryption (password)
- PDF/A (archival PDF)
- Peer-to-peer (P2P) transfer
- PEF (Pentax RAW)
- Perceptual Hash
- PFB (PostScript font)
- PFM (font metrics)
- PGM
- pHash (DCT Hash)
- PHAsset
- PHAssetResource
- PHImageManager
- Phone Storage Fragmentation
- Photo Cache vs Photo Storage
- Photo Deletion Flow (PhotoKit)
- Photo Library Permission
- PhotoKit
- Photos library (Mac)
- PII (personally identifiable information)
- Pixelation
- PKG (installer)
- Plain text (.txt)
- PLIST (property list)
- PLY (Polygon)
- PNG
- PostScript Type 1 font
- PPM
- PPTX (PowerPoint)
- PRC (Mobipocket)
- Prefetch / preload cache
- Product photo
- Progressive JPEG
- Progressive vs Baseline JPEG
- ProRAW File Size
- ProRes (Apple)
- Provisioning Profile
- Proxy server
- PS (PostScript)
- PSB (large Photoshop)
- PSD (Photoshop document)
- PUB (Publisher)
- Purgeable space
- Purgeable Space Internals
R
- RAF (Fujifilm RAW)
- RAID (0/1/5/10)
- RAR
- RAW image
- RAW vs JPEG Storage
- Raw vs Usable Capacity
- READ_MEDIA_IMAGES / VIDEO
- RealAudio (.ra)
- Recently Deleted
- Recycle Bin
- REG (Windows Registry file)
- Remuxing
- requestLegacyExternalStorage
- Residual Files
- Responsive Images (srcset)
- RMVB / RM (RealMedia)
- robots.txt
- Rolling shutter
- Room Persistence Library
- RPM (Red Hat package)
- RTF
- Runtime Permissions (Android)
- RW2 (Panasonic RAW)
S
- Safari Website Data
- Scoped storage
- Scoped Storage Internals
- Screen recording
- Screenshot
- Screenshot Storage Cost
- Searchable PDF
- Secure deletion (file shredding)
- Secure Folder
- Selective sync
- Service worker (offline cache)
- Session storage
- SFD (FontForge)
- SGI / RGB image
- SHA-256 Checksum
- Shader cache
- Shared with You
- SharedPreferences
- Similar photos
- Site data
- SKP (SketchUp)
- Slack Space
- Slow-motion video
- Smart Storage
- SoftwareApplication Schema
- Sparse File
- Sparse image (Mac)
- Speex (.spx)
- Split APKs
- Spotlight index
- SQL file (.sql)
- SQLite
- SQLite Auto-Vacuum
- SQLite VACUUM
- SQLite WAL Mode
- SRT (SubRip subtitles)
- SRW (Samsung RAW)
- SSD (solid-state drive)
- SSD vs HDD
- STEP (.stp CAD)
- STL (3D printing)
- Storage Access Framework
- Storage Bottleneck
- Storage optimization
- Storage Permission Changes by API Level
- Storage Sense (Windows)
- Storage Volumes (Android)
- Storage vs RAM
- StorageManager (Android)
- StorageStatsManager
- Streaming App Cache
- Structured data (schema markup)
- StuffIt (.sit/.sitx)
- SVG
- Swap partition / swap file
- Swap Space
- SWF (Flash)
- Symbolic Link
- Sync conflict
- System Data
- System Data (Mac)
- System Reserved Storage
- System Restore point
- System storage (Android)
- System Update Leftovers
T
- TAR
- Temporary files
- temporaryDirectory (iOS)
- Tethering / hotspot
- TEX (LaTeX)
- TGA (Targa)
- TGZ (.tar.gz)
- Thumbnail
- Thumbnail cache
- Thumbnail cache (Windows)
- Thumbnail Generation
- Thumbnail Stripping
- TIFF
- Time Machine
- Time-lapse
- tmpfs
- Toast (.toast)
- TOML (config)
- Transcoding
- Transparent background
- Trash (Mac)
- Trash / Recycle Bin (Android)
- TRIM (SSD)
- Trim Memory Levels
- TRIM vs Discard
- TRP / TS recording
- TS (MPEG transport stream)
- TSV
- TTF (TrueType font)
- TTML
- Two-factor authentication (2FA)
- Two-Pass Encoding
U
V
W
- WAR (Java web archive)
- WASM (WebAssembly)
- Watermark
- WAV
- WavPack (.wv)
- WBMP
- Wear Leveling
- Web Image Compression
- WebM
- WebP
- WebVTT (.vtt subtitles)
- wHash (Wavelet Hash)
- White background (product photo)
- White balance
- Wi-Fi vs cellular data
- WIM (Windows image)
- Windows Registry
- Windows temporary files
- Windows Update cleanup
- WinSxS folder
- WMA
- WMV (Windows Media Video)
- WOFF (web font)
- WOFF2 (web font)
- WorkManager
- WPD (WordPerfect)
- WPS (Microsoft Works)
- Write Amplification
- WTV / DVR-MS
X