I've used Windows 10 since the launch, but the File Compress Utility process(compact.exe) suddenly started to compress my hard disk a few days ago. I didn't touch any settings on the system. Why is this happening at all? It's not just the operating system files, but several folders in my home are compressed, including Desktop, AppData, and .android. Is there a way to know which files are affected so that I can uncompress them?

I enabled Do not allow compression on all NTFS volumes, and also ran compact.exe /CompactOS:never, and the compressing somehow stopped, but it's running again now. Running compact.exe /CompactOS:Query reports it's in the compact state.

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  • What size is your operating system partition? I've seen some news that on tablets and devices with limited storage that compaction is intended to be used to reduce operating system footprint and free up storage. – Mokubai Dec 5 at 8:57
  • @Mokubai I'm using 256GB SSD, and I think I had more than 5GB free space left. – alice Dec 5 at 9:17
  • 5GB is cutting it close with some Windows updates, especially the feature updates, and Windows will ignore your settings about compaction to allow it to install such updates (though it will usually uncompress things it compressed afterwords, which sometimes leads to the irritating situation that it uncompressed things which you wanted compressed). Unless you've got a really crappy CPU though, having transparent compression enabled probably won't hurt performance, and it can save a lot of space. – Austin Hemmelgarn Dec 5 at 20:21

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