Have you noticed that an XP machine that is left turned on overnight, appears to be slow? It does not appear to be slow, but is slowed down.
When your PC running XP is left idle, processes like virus scanning, indexing and defragmenter start executing. The memory allocated to the applications you normally used is now allocated to these processes. Your applications are moved to a page file on the hard drive. Now when you try and open these applications, the operating system has to copy the application back into memory from the hard drive. This takes some time and results in decrease of responsiveness.
This problem has been addressed in Vista. Vista comes with SuperFetch to enhance performance of your system. SuperFetch monitors your application usage and tries to make these applications more responsive by placing them in the memory, ready to start. When a PC running Vista is left idle, the processes I mentioned above, like indexing and virus scanning get invoked and perform their tasks. This causes your favorite applications to be pushed in to the page file on the hard disk. When these processes complete execution, SuperFetch fetches your applications from the page file into the main memory (with out you invoking them). So the next time you try starting those applications, they are up and running in no time.
As you might have understood by now, SuperFetch is a very useful service and disabling it is not recommended.
