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"Mem Usage" higher than "VM Size" in WinXP Task Manager

Asked 2008-10-31T04:31:42.350
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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 and 100576 K as VMSize.

According to the help file of Task Manager Mem Usage is the working set of the process and VMSize is the committed memory in the Virtual address space.

My question is, if the number of committed pages for a process is A and the number of pages in physical memory for the same process is B, shouldn't it always be B ≤ A? Isn't the number of pages in physical memory per process a subset of the committed pages?

Or is this something to do with sharing of memory among processes? Please explain. (Perhaps my definition of 'Working Set' is off the mark).

Thanks.

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XP's Task Manager is simply wrong. EDIT: If you don't believe me (and someone doesn't, because they voted this down), read Firefox 3 Memory Usage. I quote:

If you’re looking at Memory Usage under Windows XP, your numbers aren’t going to be so great. The reason: Microsoft changed the meaning of “private bytes” between XP and Vista (for the better).

Sounds like MS got confused. You only change something like that if it's broken.

Try Process Explorer instead. What Task Manager labels "VM Size", Process Explorer (more correctly) labels "Private Bytes". And in Process Explorer, Working Set (and Private Bytes) are always less than or equal to Virtual Size, as you would expect.

answered 2008-10-31T07:24:09.910

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