What exactly is the PF (Page File) Usage thingy in the windows task manager in XP???

Answer 1

Hello,

Page file is the file used by OS to implement Paging.

paging: You know that system cache and RAM are very costly. SO What OS does is, move less used parts of huge programs to the hard drive, so that they can be used when it is required.

You can see more details about this with some examples at
http://en.wikipedia.org/wiki/Paging

take care
Pachu

Answer 2

http://www.forensics-intl.com/def7.html

This site can probably explain it to you better than me, but basically it is part of your hard disc used by windows when it needs extra memory. The larger it is, the faster windows will run.