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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, 2018 at 8:57
  • @Mokubai I'm using 256GB SSD, and I think I had more than 5GB free space left.
    – alice
    Dec 5, 2018 at 9:17
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    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. Dec 5, 2018 at 20:21
  • winaero.com/blog/compress-files-folders-windows-10 is helpful to see how to toggle the option in Properties. Once the compact.exe is started when your disk space is low, however, it doesn't seem to stop, even if you've freed up space and/or toggled the option in folders/files. Mar 29, 2019 at 9:58
  • 5/256GB is just ~2% free disk space which will may exceeded easily just in a few minutes, so you definitely need to make some more space. The myth that Compact OS always makes it slower is false. See Is “compress OS Drive” worth it on SSD?
    – phuclv
    Feb 14, 2021 at 0:49

1 Answer 1

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This might be caused by KB4023057, which "may take steps to free up disk space on your device if you do not have enough disk space to install Windows updates."

You can uninstall it from Programs and Features, and can block it from installing again using this troubleshooter.

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