What is page files?

[SweatyOgre]

Sorry, I got a new comp with Win XP yesterday after using Win 98 for 6 years, and Page File Usage is mentioned nowhere in Windows 98. When I hit ctrl+alt+delete and bring up the task manager, under the performance tab, Page File Usage is one of the statistics. What is this? Also, what is the "Commit Charge:" number in the bottom right hand corner?

 

[Stryder]

Page file(virtual memory) is ram, but uses the hard drive for it.

Note:You can adjust how much Paging is allow.

Commit Charge-the Windows operating system, the name for the amount of physical memory (RAM) and virtual memory that is allocated to all running programs, or applications, and the operating system itself.

I got umm lets say, 133/1506 commit charge.
133 is how much ram im using ATM, 1506 is the max i can use.