“Mem Usage” higher than “VM Size” in WinXP Task Manager

Question

In my Windows XP Task Manager, some processes display a higher value in the Mem Usage column than the VMSize. My Firefox instance, for example shows 111544 K as mem usage an

Answer 1

File mapping

Very common way how Mem Usage can be higher than VM Size is by using file mapping objects (hence it can be related to shared memory, as file mapping is used to share memory). With file mapping you can have a memory which is committed (either in page file or in physical memory, you do not know), but has no virtual address assigned to it. The committed memory appears in Mem Usage, while used virtual addresses usage is tracked by VM Size.

See also:

What does “VM Size” mean in the Windows Task Manager? on Stackoverflow

Breaking the 32 bit Barrier in my developer blog

Usenet discussion Still confused why working set larger than virtual memory