Superfetch??

What is Superfetch?? Quite often i get a message popping up saying this has stopped working and often get a message about something to do with Host Service has stopped working.
What do these mean exatly as it is rather annoying.
I have noticed that when one of these messages has popped up Windows Aero does not function untill a restart has been done. and no doubt this is related somehow.
I know i have all the latest drivers for all applications that need them and Windows is upto date too.

Thanks all.

Phil.

Here's some info on Superfetch:

Windows Vista I/O technologies - Wikipedia, the free encyclopedia