How is the Page File available calculated in Windows Task Manager?

Question

In Vista Task Manager, I understand the available page file is listed like this:
Page File inUse M / available M
In XP it's listed as the Commit Charge Limit.

I had thought that:
Available Virtual Memory = Physical Memory Total + Sum of Page Files

But on my machine I've got Physical Memory = 2038M, Page Files = 4096M, Page File Available = 6051. There's 83M unaccounted for here. What's that used for. I thought it might be something to do with the Kernel memory, but the number doesn't seem to match up?

Info I've found so far:

• See http://msdn.microsoft.com/en-us/library/aa965225(VS.85).aspx for more info.
• Page file size can be found here: Computer Properties, advanced, performance settings, advanced.

Answer 1

Shared memory used by the GPU?

Answer 2

I think you are correct in your guess it has to do something with the kernel - the kernel memory needs some physical backup as well.

However I have to admit that when trying to verify try, the numbers still do not match well and there is a significant amount of memory not accounted for by this.

I have:

Available Virtual Memory = 4 033 552 KB

Physical Memory Total = 2 096 148 KB

Sum of Page Files = 2048 MB

Kernel Non-Paged Memory = 28 264 KB

Kernel Paged Memory = 63 668 KB