File system
Also known as: filesystem, what is a file system, disk format
A 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).
- Organizes files, tracks their location, manages free space
- APFS = Apple, NTFS = Windows, exFAT/FAT32 = cross-platform
- Formatting writes a fresh file system and erases data
What a file system does
Raw storage is just a sea of empty blocks. A file system is the index and rulebook on top of it: it gives files names and folders, remembers exactly which blocks hold each file, and keeps track of what space is free. Without one, the device cannot tell a photo from empty space.
Each operating system has a preferred format. Apple uses APFS, Windows uses NTFS, and removable drives often use exFAT or FAT32 so they work across systems.
Why formatting matters
Formatting a drive writes a fresh, empty file system onto it, which is why it erases everything. The format you choose decides compatibility and limits — for example, FAT32 cannot hold a single file larger than 4 GB, while exFAT and APFS have no practical file-size cap for everyday use.