Systems like Windows XP require more operational memory than most systems have installed
as actual "physical memory".
All modern operating systems handle this by using "Virtual Memory" : memory, which does
not exist as physical existing memory chips, but has emulated memory by using a part of the
disk to temporary store information, which is currently not used by the CPU, from physical memory
to disk, to make room for information currently used by the CPU. if such information placed on the
disk is required by the CPU at a later time, other information in memory is store to disk, making
space for the needed information to be put back into physical memory.

Since information be be swapped several time between physical memory and the disk, the file
on the disk used to store memory information is often called "Swap-file".
Since the information is swapped in fixed size units called "Pages", the file is also call "Page File".

The Windows Task-Manager is giving you an overview on the usage of the PF = Page-File :

It is very important, that XP never runs out of memory :
If Task Manager shows that you get close to the limit , either install more physical memory chips
(best solution) or increase the size of the Page-File :

	In the Control-Panel, select the System icon: (or right-click "My Computer" on the desktop and select Properties) Select the tab: "Advanced" and then use in the section "Performance" the button "Settings"
	In the Window "Performance Options", use the tab : "Advanced" In the section "Virtual Memory", the system shows the total size of the Paging file, which you can increase with the "Change" button. "
	Usually, Windows stores the Paging File on drive C:, but if you are short on disk-space on drive C:, you can place a Paging File on a different disk and then decrease the size of the paging file on the C-drive. When using a Application, which use a lot of memory and therefore use heavily the memory emulated by the paging files, it is strongly suggested to increase the "Initial Size" of the Paging file, which reserves already the space on the disk for the page-file.