Clearing Out Windows Prefetch for Faster Startup

The Prefetch feature in Windows XP caches parts of applications that you frequently use and tries to optimize the loading process to speed up application start time, so when a number of sites started suggesting that you clean it out regularly to speed up boot time it seemed like good advice... but sadly that's not the case, as pointed out by many Lifehacker commenters.

The Prefetch feature is actually used as a sort of index, to tell Windows which parts of an application should be loaded into memory in which order to speed up application load time, but Windows doesn't use the information unless it's actually starting an application. There's also a limit of 128 files that can be stored in the prefetch folder at any point, and Windows cleans out the folder automatically, removing information for applications that haven't been run as frequently. Not only that, but a well-written defrag utility will use the prefetch information to optimize the position of the files on the disk, speeding up access even further.

Windows expert Ed Bott explains it:

The .pf files don’t get used at all until you run a program. What actually happens when you click an icon is that Windows uses the information in the Prefetch folder to decide which program segments to load and in what order to load those pages.