“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

Memory usage is the amount of electronic memory currently allocated to the process.

VM Size is the amount of virtual memory currently allocated to the process.

so ...

• A page that exists only electronically will increase only Memory Usage.
• A page that exists only on disk will increase only VM Size.
• A page that exists both in memory and on disk will increase both.

Some examples to illustrate:

Currently on my machine, iexplore has 16,000K Memory Usage and 194,916 VM Size. This means that most of the memory used by Internet Explorer is idle and has been swapped out to disk, and only a fraction is being kept in main memory.

Contrast with mcshield.exe with has 98,984K memory usage and 98,168K VM Size. My conclusion here is that McAfee AntiVirus is active, with at lot of memory in use. Since it's been running for quite some time (all day, since booting), I expect that most of the 98,168K VM Size is copies of the electronic memory - though there's nothing in Task Manager to confirm this.