Is it safe to delete Prefetch files?

You can delete the files in C:\Windows\Prefetch without breaking anything, but there's almost no reason to. They are small, Windows manages the folder on its own, and it rebuilds the files the next time you open each program. Emptying it can even make your apps start slower for a while.

Quick verdict:

• Safe, but pointless: the .pf files in C:\Windows\Prefetch. Deleting them frees little space and takes away a speed-up.
• Not a real fix for a full disk or a slow PC. Look for bigger folders first.
• Leave alone: the SysMain service and the Prefetch registry settings. Changing them doesn't save disk space.

What is the Prefetch folder?

Prefetch is a Windows feature that remembers what a program loads when it starts, so the next start can be faster. Microsoft's documentation for the Enable-MMAgent cmdlet describes it this way: application launch prefetching watches the data and code an app reads, then preloads it into memory for later startups.

The files live in:

C:\Windows\Prefetch

Inside you'll find:

• .pf files, one per program, named like CHROME.EXE-1A2B3C4D.pf. The part after the dash is a hash of the folder the program ran from, so the same app run from two places gets two files.
• Layout.ini, which Windows uses to arrange startup files efficiently on disk.
• On some PCs, Ag*.db files and a ReadyBoot subfolder, used by the memory manager (once called Superfetch) for boot and app preloading.

The service behind all this is SysMain, the name Windows 10 and 11 use for what was once Superfetch. You can see it in the Services app (services.msc).

Why does it keep growing back?

Because every new program you run gets its own .pf file. Windows caps the number of files and removes the oldest ones on its own. Forensic researchers report a limit of about 1,024 files on Windows 8 and later, up from 128 on Windows 7. The folder doesn't grow forever.

How much space does it use?

Usually very little. Each .pf file is small, typically a few kilobytes to a few hundred, and the folder as a whole is rarely what fills a drive. Check your own PC rather than trusting a number:

1. Open File Explorer and paste C:\Windows\Prefetch into the address bar.
2. Windows says you don't have permission. Click Continue and approve the administrator prompt.
3. Select all files (Ctrl+A), right-click, and choose Properties to see the total size.

You can also use PowerShell as administrator:

(Get-ChildItem C:\Windows\Prefetch -Recurse | Measure-Object Length -Sum).Sum / 1MB

With SquirrelDisk, scan your C: drive and click into Windows to see how Prefetch compares with the folders around it. SquirrelDisk runs as your normal user, without admin rights, so it may skip folders your account can't read, and Prefetch can show as smaller than it is. That's fine for this purpose: if it doesn't stand out among the big slices, it isn't your problem. SquirrelDisk won't delete anything inside C:\Windows, so use Windows itself for that.

How to delete it safely

There's no Prefetch entry in Disk Cleanup or Storage Sense, because Microsoft doesn't consider it junk. If you still want to empty it, for example while troubleshooting:

1. Save your work and close your apps.
2. Open File Explorer and go to C:\Windows\Prefetch. Click Continue at the permission prompt.
3. Select the .pf files and delete them. Leave the ReadyBoot folder and the .db files alone if you see them; Windows uses them too.
4. If a file says it's in use, skip it.
5. Restart. The first starts of Windows and your programs may be a little slower while new files are recorded.

There's no need to repeat this. The folder fills up again with normal use.

What you should not do

• Don't disable SysMain or set EnablePrefetcher to 0 to "save space". Many old tweaking guides suggest it. It saves almost no disk space and can make startups slower. If you have a specific problem, change it as a test and set it back afterwards.
• Don't add Prefetch to a scheduled cleaner. Clearing it every day means Windows never gets the benefit.
• Don't panic about unfamiliar names. A .pf file only means a program ran at some point. It isn't the program itself, and deleting it doesn't uninstall anything. If a name worries you, look for the program it belongs to and scan that with your antivirus.

If you did change SysMain, open Services, find SysMain, set Startup type to Automatic, and click Start.

Better ways to free space

If your C: drive is full, the space is almost certainly somewhere else. Places that are often much bigger:

• Leftover update files: see is it safe to delete the SoftwareDistribution folder and Windows.old.
• Temporary files: see is it safe to delete temp files. Settings → System → Storage → Temporary files handles most of them safely.
• Your own downloads, videos and old installers, which a disk analyzer like SquirrelDisk shows in seconds.