Windows XP has a Prefetcher component, which shortens the amount of time it takes to start Windows and programs. When trouble shooting either Windows or program start-up issues, it might be helpful to disable the prefetcher, because it runs as a background service while other applications are running or loading.

One of the hidden features in Windows XP (only) is the prefetcher. It, quite simply, works to speed up the launch of applications by loading them before you access them. It primarily works by loading startup programs during the time windows is still booting so that when you enter your password, everything loads quickly. It also keeps a record of all programs launched and how much they are used to aid in allocating how much prefetching to which program.

Contrary to popular belief, it is not responsible for making windows boot as fast as it does. In fact, the prefetcher only makes that it longer, since with the prefetcher activated it uses that period of time to load the other stuff that's going to load. But this is still a good thing, as it is annoying to continue waiting for stuff to load after you enter your password. The prefetcher works to take all the loading to the windows boot logo stage to make everything else that requires your interaction faster.

The prefetcher has a file for each program that you run that, in part, records the amount of use. Logically, programs that are loaded often are prefetched more than programs that are not.

The prefetch files are located in %windir%\prefetch. That's C:\windows\prefetch for those who don't know. If you opened it now you would see a whole bunch of .pf files and one layout.ini file. All the .pf files are individual recoards of each program. The layout.ini file is a consolidation of all those programs and what they typically access, in order of priority.