With both Windows XP and Windows Vista, you may have noticed a folder in the Windows directory named Prefetch. Inside this folder, you will see quite a few files (up to 128 total) that have the extension of '.pf'. What exactly is prefetch and what does it do?

Prefetch files are sort of miniature index files that tell the computer what files are associated with a given program and where those files are located on the hard drive. The idea is to make programs load faster and without errors when you launch them. However, this leads to some less than correct beliefs.

One of the biggest of these fallacies is that prefetch somehow has a great impact on how fast Windows boots up. Some individuals have gone so far as to say that removing the files from the prefetch folder will speed up the computer as well as shortening the time it takes for the computer to boot up.

The fact is that prefetch files have little to do with boot speed. The computer only reads a prefetch file when the program it is associated to is launched. This means that except for the prefetch files related to programs that are set to launch on bootup, these files aren't going to be read until programs are actually started, and there will be very little impact on how fast the computer boots up.

Removing the files also won't do much to speed up the computer for a couple reasons. The first is that the prefetch file will be rewritten as soon as each program launches. If anything, it will cause a slowdown until all the files are written, so each time a program is launched for the first time after removing the files, it will take a little longer to load than normal.

Second, there are a maximum number of files allowed in the folder, and Windows automatically gets rid of older files once that maximum is reached. The files aren't large in any event, so if they have a negative impact on the amount of hard drive space that is available, it is likely that the hard drive needs to be cleaned to free up more space.

A valid question is whether prefetch really does allow programs to load faster. The answer is almost certainly yes, however with modern high speed computers, the time savings are probably going to be so slight that you wouldn't be able to tell much difference.

Still, since the prefetch files do tell the computer what components should be loaded with a given program, as well as where those components are located on the hard drive, prefetch does tend to eliminate many of the errors that were common before the prefetch folder was thought up and put into place. The old 'file not found' messages that used to be so often seen are now pretty rare, for instance.

Prefetch serves a useful purpose, and understanding that purpose isn't really difficult as long as you just remember that it is to aid the computer in opening programs.

Learn more about this author, Rex Trulove.
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