The "Prefetch" Folder

\windows\prefetch

The "windows\prefetch" folder is there for one reason - to speed up the loading (starting) of applications.  Win XP uses ‘pre-fetching’ to load drivers, services and the shell into memory before they are actually needed.

Can I Delete the Prefetch files?  YES, and actually, you SHOULD delete them periodically.  Over time you will get more and more entries in the prefetch folder - including spyware !!!  Your apps will load a bit slower, since prefetch speeds them up - but XP will rebuild the prefetch files as you use Windows - so no worry !!

Win 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 WINDOWS\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. 

To see the effect of not having prefetch data, simply delete the files for a corresponding application, and start it to see the difference. For instance, if you have Microsoft Word, first run it a few times if you haven’t already done so and use it normally. Then record the time that Word takes to start up from the moment you click its icon. Now delete the files WINWORD.EXE.*.PF (see box on what these filename formats are) from WINDOWS\PREFETCH. Start Word again using its icon and measure the startup time. You’ll see a major difference in the two. But no problem, Win XP will start collecting prefetch data for the application again and a few launches later you’ll get the quick start again. There is also a file for the boot loader that works in the similar way.

The prefetch data is also used in the Win XP defrag application.

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 Win XP automatically runs defrag when it detects an idle computer and tries to change the layout of the files.