CompactOS is a built-in feature in Windows 10 and Windows 11 that compresses the operating system files (primarily system binaries in the Windows directory), allowing the OS to run directly from these compressed files. This reduces the disk space used by Windows itself, typically saving 2–4 GB or more depending on the installation.
It was introduced in Windows 10 to help low-storage devices (like tablets or laptops with small SSDs, e.g., 32–64 GB drives) fit the OS comfortably. Unlike regular NTFS drive compression (which compresses everything on the drive), CompactOS targets only core OS files and uses efficient algorithms (such as XPRESS4K, XPRESS8K, XPRESS16K, or LZX) via the Windows Overlay Filter (WOF). It can be enabled or disabled on a running system without reinstalling Windows.
Key Benefits
- Saves significant disk space on the system drive.
- Windows updates can still manage files by replacing or removing them as needed.
- Supported on both UEFI and BIOS-based devices.
Potential Drawbacks
- Slight increase in CPU usage for on-the-fly decompression.
- Minor impact on performance (e.g., boot times or file access), especially on older/low-power hardware.
- On modern fast SSDs and powerful CPUs, the performance hit is often negligible or even unnoticeable.
How to Manage CompactOS
Use the compact.exe command in an elevated Command Prompt (run as administrator):
- Check status: compact /compactos:query (It will say if the system is compacted, not compacted, or can compact as needed.)
- Enable always: compact /compactos:always (Forces compression; takes time to process files.)
- Disable: compact /compactos:never (Uncompresses files.)
Windows may automatically enable it on very low-storage devices during setup.
As of 2025, CompactOS remains fully supported in the latest Windows 11 versions, per Microsoft documentation and recent guides. It's particularly useful for embedded/IoT deployments or storage-constrained PCs, but less necessary on devices with large drives.
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