Prefetch are files that XP uses to start programs faster. Here is some info about Defrag
that mentions Prefetch:
Optimizing Startup Times by Using Defragmentation Tools
Windows XP Professional monitors the files that are used when the computer starts and when you start applications. By monitoring these files, Windows XP Professional can prefetch them. Prefetching data is the process whereby data that is expected to be requested is read ahead into the cache. Prefetching boot files and applications decreases the time needed to start Windows XP Professional and start applications.
Prefetching is further improved if the files are located next to each other on the outer edge of the disk. Windows XP Professional optimizes the location of boot files and applications when the computer is idle. The optimization occurs in the background and lasts only a minute or two; you might hear the hard disk being accessed when optimization occurs. After the initial optimization takes place, subsequent optimization occurs, at most, every three days.
When you run the Disk Defragmenter tools that are included with Windows XP Professional, they can perform any optimization updates that are scheduled to take place during the next idle period. The Disk Defragmenter tools do not disturb the existing layout of optimized boot files and applications.
Note
* Computers running Windows XP Home Edition also prefetch and optimize boot files and applications.
