By default, the prefetch folder is set for Windows to keep it to 128 entries over three weeks, and it isn't files in full but a directory os where files are so Windows can find them quickly instead of scanning your hard drive every time you start an ap, etc.
Pruning or cleaning it yourself, or limiting it will cause your aps to take longer to open.
Read the following before you mess with it:
Prefetch warning and linkshttp://www.edbott.com/weblog/archives/000743.htmlhttp://www.langa.com/newsletters/2005/2005-04-07.htm#3
Prefetch Pros and Conshttp://langa.com/newsletters/2002/2002-12-12.htm#9
"I've found many web sites recommending a way of speeding up boot times that might in fact slow down the amount of time it takes to boot up and will probably slow down launching applications as well. The tip recommends going to your C:\WINDOWS\Prefetch directory and emptying it every week. Windows uses this directory to speed up launching applications. It analyzes the files you use during startup and the applications you launch, and it creates an index to where those files and applications are located on your hard disk. By using this index, XP can launch files and applications faster. So, by emptying the directory, you are most likely slowing down launching applications. In my tests, I've also found that after emptying the directory, it takes my PC a few seconds longer to get to my desktop after bootup."http://www.langa.com/newsletters/2005/2005-04-07.htm#3
XP systems have a Prefetch directory underneath the windows root directory, full of .pf files — these are lists of pages to load. The file names are generated from hashing the EXE to load — whenever you load the EXE, we hash, see if there’s a matching (exename)-(hash).pf file in the prefetch directory, and if so we load those pages. (If it doesn’t exist, we track what pages it loads, create that file, and pick a handful of them to save to it.) So, first off, it is a bad idea to periodically clean out that folder as some tech sites suggest. For one thing, XP will just re-create that data anyways; secondly, it trims the files anyways if there’s ever more than 128 of them so that it doesn’t needlessly consume space. So not only is deleting the directory totally unnecessary, but you’re also putting a temporary dent in your PC’s performance. [emphasis in original]
Bottom line: You will not improve Windows performance by cleaning out the Prefetch folder. You will, in fact, degrade Windows performance by cleaning out the Prefetch folder. I’ve done performance testing that establishes this definitively. In all the many sites that offer this bogus tip, I have yet to see a single piece of actual performance testing.http://www.edbott.com/weblog/archives/000743.html