page file is basicly memory on your harddrive, used to store memory that mostly just needs to be stored by applications, (not a programmer but, im guessing its more of the temporary data that doesnt change much, sortof), normally its set to bout 2gigs or 4gigs, but you can make it as big as u want, windows7 and versions before that eat more and more memory, and alot of it is stored in the page file. default set pagefile on the same drive/partition as your installation, by choosing another not so much used harddrive say your storage harddrive, and upping it a few gigs, can increase your overall performance, in games, apps, etc. alot of the crashes with wow/hb2/gb seem to be memory related, and alot of software these days are prown to memory leaks, so having a nice big page file can help prevent or prolong crashes. this is based on my knowlege wich isnt exact ;P.