|Prefetch is one of the most misrepresented features of XP. There are a large number of Internet articles that supposedly describe how it works and how you can modify it for your own benefit. Unfortunately, most of these articles are wrong, many are mostly nonsense.|
It is widely believed, largely because of misinformed Internet articles, that XP looks in the prefetch folder at bootup and then proceeds to preload everything it finds there. That isn't even close to reality. In fact, application prefetch files aren't even looked at until the application is launched. These files contain information gained from previous experience on how to more efficiently launch an application. To understand how that works you need to first understand how a modern virtual memory operating system works and that is not simple.
Why would you want to decrease the size of the system cache? This cache greatly benefits system performance and reducing it's size will almost always be harmful.