Open Settings > System > Storage on Windows 11 and the System & reserved category often shows 20–40 GB. That number is not one thing — it is the sum of four distinct allocations Windows makes for itself.
Short answer: it is mostly Reserved Storage (set-aside space for future updates), the paging file, the hibernation file, and system files. You can shrink Reserved Storage, turn off hibernation, and cap the page file, but you should not touch the core system files.
The four things inside "System & reserved"
- System files — the OS itself (
C:\Windows, drivers, core binaries). Usually 15–25 GB. Not removable. - Reserved Storage — introduced in Windows 10 1903, this is ~7 GB that Windows holds back specifically so feature updates have room to install. Without it, updates fail on near-full drives.
- Page file (
pagefile.sys) — virtual memory. Default size scales with installed RAM. Usually 2–16 GB. - Hibernation file (
hiberfil.sys) — a snapshot of RAM for fast startup and hibernation. Roughly 40–75% of installed RAM.
How to shrink each piece
Turn off hibernation (biggest win on laptops with lots of RAM)
- open Command Prompt as administrator
- run
powercfg -h off - reboot —
hiberfil.sysis gone
This disables hibernation and Fast Startup. Sleep still works. Full walkthrough: How to Disable Hibernation to Save Gigabytes of Space.
Disable Reserved Storage
- open Command Prompt as administrator
- run
DISM.exe /Online /Set-ReservedStorageState /State:Disabled - reboot
This frees ~7 GB but makes future feature updates riskier on a tight drive.
Cap the paging file
- press Windows + R, type
sysdm.cpl, press Enter - Advanced tab > Performance > Settings > Advanced > Virtual memory > Change
- untick Automatically manage, set a custom maximum (for example 4096 MB for systems with 16 GB+ RAM)
Do not set it to zero — Windows and some apps will fail.
Better next routes
For removing the old install folder that often hides in "System & reserved," continue with How to Delete the Windows.old Folder (If Disk Cleanup Fails).
For a full Windows 11 cleanup, read How to Free Up Space on C Drive Windows 11 Natively.