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Commit charge doesn't match addition

Posted on 2004-09-27
Medium Priority
Last Modified: 2008-01-09
What exactly is commit charge?  I always assumed it was a sort of "total memory usage".  However, if I add up all the programs "Mem Usage" I get about 60mb worth of stuff in memory.  My commit charge is over 200.
I also saw a "Virtual-Memory" tab, and found that a lot of my programs have large chunks of virtual memory.  Is there any way to tell XP to go ahead and actually GIVE them that memory?  I'm tierd of having 256mb, and only having XP fill 70-80ish with programs, and paging out the rest to disk.
Question by:CmdrRickHunter
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Assisted Solution

Kenneniah earned 300 total points
ID: 12161633
Total memory usage is more than just the programs you have running. Not all the memory the OS is using shows up in the process list. Things like cache and reserved memory etc. Also, programs request memory to be reserved for them, whether they are currently using that much or not. So a program might only be currently using 10MB, but the system has reserved 20MB for it etc.

As for disabling virtual memory, it is usually not a good idea. The entire memory system in XP is based on paging, and it actually is more efficient than not paging unless you have an extreme amount of physical memory. One of the best explainations (and also covers the previous question talking about programs asking for more memory than they are using) is found at http://aumha.org/win5/a/xpvm.php
Quoted from there:
"Can the Virtual Memory be turned off on a really large machine?
Strictly speaking Virtual Memory is always in operation and cannot be “turned off.” What is meant by such wording is “set the system to use no page file space at all.”

Doing this would waste a lot of the RAM. The reason is that when programs ask for an allocation of Virtual memory space, they may ask for a great deal more than they ever actually bring into use — the total may easily run to hundreds of megabytes. These addresses have to be assigned to somewhere by the system. If there is a page file available, the system can assign them to it — if there is not, they have to be assigned to RAM, locking it out from any actual use."

Accepted Solution

TomJ76 earned 700 total points
ID: 12164781
When you add up your Applications' Mem Usage up and notice that the number fails to line up with your Commit Charge Total, you'll have to remember that number INCLUDES your operating system. The OS doesn't show up anywhere in your Applications tab.
Some, if not all, of the RAM the OS uses will show up in the bottom right corner of the Task Manager's Performance Tab screen in the Kernel Memory area.
I have to second the observations that Kenneniah has made about Virtual Memory in Windows XP. Basically, if you didn't help Microsoft develop XP and thus know some secrets the rest of us don't, leave Virtual Memory turned on.

For your reference, Webopedia defines "Commit Charge" as below, per http://www.webopedia.com/TERM/C/commit_charge.html
(k&-mit´ chärj) (n.) In the Windows operating system, the name for the amount of physical memory (RAM) and virtual memory that is allocated to all running programs, or applications, and the operating system itself.

Windows Task Manager displays the commit charge in its Performance tab. There are three memory readings, measured in kilobytes:

    * Total: refers to the total amount of physical and virtual memory the computer is using at that moment.
    * Limit: refers to the combined limit of both the physical memory and the allocated virtual memory.
    * Peak: refers to the highest total system memory usage during the session in which you are using the computer.

The commit charge will increase when applications are opened and used and decrease when applications are closed.

Author Comment

ID: 12165671
Its not so much that I want to turn VM off, but I want XP to use my physical memory properly.
I have 256mb of memory.  When I get to the point where I'm using about 200 (commit charge) of it, my harddrive starts thrashing madly whenever I move from one application to annother, something I attribute to page faults.  I've gotten better results since telling windows to optimize the "system cache" instead of "programs", which is counterintuitive, but it works.  However, As I approach 256mb of commit charge, I see, again, my harddrive thrashing (i'm assuming) paging programs in and out.

A friend mentioned that windows XP was optimized for 128mb of memory, and handles memory beyond that very poorly... is this true?
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Expert Comment

ID: 12172007
A friend mentioned that windows XP was optimized for 128mb of memory, and handles memory beyond that very poorly... is this true?

With all due respect to your friend, who I am certain is an upstanding individual, he or she has been misinformed. My home system has 512 MB of RAM, and seems to handle that RAM quite nicely. My desktop PC at work has 256 MB, and seems to handle that amount of RAM politely as well.


Expert Comment

ID: 12172648
 As I approach 256mb of commit charge, I see, again, my harddrive thrashing (i'm assuming) paging programs in and out.

That's pretty much a design trait for any OS that uses virtual memory..
The way this was explained to me, your system needs to start freeing up free space when it approaches the edge of its physical memory. It offers you slowed performance as you approach the edge of free space as an alternative to giving you full performance up to the edge of free space and then abruptly offerring you several seconds of *NO* performance when it hits the edge.
I believe this behavior is an accepted design trait to the point that Windows XP and Linux both behave in the same fashion.
If you find yourself "approaching the edge" more than three or four times a day, it might be time to consider a memory upgrade. If you multi-task heavily with large applications, 256 MB may be just barely enough.
I hate to see a question on Experts-Exchange and say "add more RAM", because that is an over-used solution, but you might be in a place where that's the right advice.
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Expert Comment

ID: 12176691
The more RAM you through at Windows XP the better. In actual usage the minimum amount I'd personally ever build into a system with XP is 512MB.

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