Windows XP Prefetch

The windows prefetch folder is there for one reason - to optimise application loading. XP uses pre-fetching to load drivers, services and the shell into memory before they are needed.

XP continually studies previous boots and optimizes the load pattern for the necessary files. This process is also applied to applications on the system. Every application is analyzed by the system when it starts up the first few times. It then creates a virtual ‘memory-map’ of what the application requires during different times of running and saves this information into the Prefetch folder. Once the mapping is done, the application loads much faster. The prefetch data is stored for the previous eight boots or application launches.

A problem with this is that XP isn't too smart about what it caches -- which includes one-time use setup files and Windows updates, as well as multiple copies of the same applications. This can lead to prefetch bloat and slower boot times.

Prefetch and Layout.ini - the most optimal prefetch order data is written to the Layout.ini file in the WINDOWS\PRE FETCH directory. You can open this file in Notepad to see the order in which XP thinks the files should be arranged physically on the disk for the fastest boot. Defrag also reads this data and arranges the files accordingly. In fact, XP automatically runs defrag when it detects an idle computer and tries to change the layout of the files.

The prefetch folder may accumulate inapplicable data, especially if you change your configuration a lot. There's no harm in emptying it. Simply delete all the files in that folder; Windows will rebuild it as needed.