Deleting Prefetch frees almost nothing, and the folder proves it
Prefetch is capped at 128 files and measured 0 MB on a real machine. The arithmetic that makes it the most overrated cleanup on Windows.
Every list of Windows cleanup tips includes emptying C:\Windows\Prefetch. It is the easiest advice to give and among the least useful, because the folder has a hard ceiling that almost nobody mentions.
The ceiling is the whole story
Windows keeps at most 128 .pf files in Prefetch. Each one records which pages an application touched as it started, and each is measured in tens to a few hundred kilobytes. Multiply the ceiling by the largest realistic file size and the folder simply cannot become a problem.
# What it is holding right now, and how many entries
$p = 'C:\Windows\Prefetch'
$f = Get-ChildItem $p -Filter *.pf -Force -EA SilentlyContinue
'{0} files, {1:N1} MB' -f $f.Count, (($f | Measure-Object Length -Sum).Sum / 1MB)Run it before you delete anything. On most machines the answer is under 100 MB, and on many it is under 20.
What you lose by clearing it
| Claim | What actually happens |
|---|---|
| Frees significant space | Tens of megabytes at most, capped at 128 files |
| Makes the PC faster | The opposite, briefly: the data is rebuilt on the next few launches |
| Fixes a slow boot | Boot tracing is separate, and rebuilding it takes several restarts |
| Removes junk left by old apps | True, and worth roughly the size of one photograph |
SysMain, which is the service behind it
SysMain, previously called Superfetch, is what writes these files. Disabling the service stops the folder growing and is sometimes suggested for the same performance reasons, which this site does not make claims about. What can be said honestly is the storage part: turning it off saves an amount of space too small to measure on any modern drive.
If the drive is genuinely full, the folders worth opening are in what is actually filling the C drive, and the list of what is genuinely safe to remove is in the folders that are safe to delete.
Common questions
Is it safe to delete the Prefetch folder?
Yes, Windows rebuilds it. It is also close to pointless: the folder is capped at 128 files of tens to a few hundred kilobytes each, so the space recovered is measured in megabytes.
How large does the Prefetch folder get?
Rarely more than about 100 MB, because Windows keeps at most 128 entries. On a machine measured in September 2026 with SysMain off, it was empty.
Does clearing Prefetch speed up Windows?
No. The files exist to make application launches faster, and clearing them means the first launch after is slower until the data is written again.
Should I disable SysMain to save disk space?
Not for space. SysMain is what maintains Prefetch, and the storage involved is too small to matter on any modern drive.