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At work, I have four system with Windows XP SP 3 with 4GB RAM installed. When I start a lot of apps, I see that Windows gets unstable when more than 2.5GB of RAM is in use with the usual effects: Explorer crashing, icons disappearing.

So it seems that Windows runs out of memory even through at least 1GB of RAM should be free (as a 32bit OS, WinXP can't use more than 3.5GB max but I'm still 1GB short).

Another thing is that Windows is trying to extend the swap file (which is set to a fixed 512MB) which isn't exactly what I want. I know that XP tries to make my system more snappy by swapping prematurely (so it can simply free pages which haven't been used for some time) but I'd prefer a system which never swaps -- I do have enough free RAM.

[EDIT] My gfx card has 512MB and the mapping is FD000000-FDFFFFFF, E0000000-EFFFFFFF and FA000000-FBFFFFFF.

This means there is a pretty big gap between EFFFFFFF and FA000000 plus a smaller one between FBFFFFFF and FD000000. This is an NVidia GeForce 8400GS. Anything I could do here to move the maps? Or can I artificially unmap part of the gfx RAM? This is my development PC, I need no 3D at all ...

[EDIT2] My device manager says that free memory goes from 0x0100'0000 to 0xDFE8'6BFF which is roughly 3.3GB. So I'm still missing 0.8GB.

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migrated from Nov 10 '09 at 18:22

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how much ram do things like your video card have? they occupy some of the physical memory space so if you have a 1GB video card, well that's 1GB of physical RAM which gets bump above the 4GB mark (which 32-bit versions of windows ignore). – Evan Teran Nov 10 '09 at 17:00
up vote 6 down vote accepted

First of all, do not statically set or get rid of your swap. Doing so is more or less saying that you know more about what is going on in the internals of your operating system than Microsoft does.

One thing to keep in mind is that all of your graphics cards, all pci devices, etc that have addressable memory on them are taking away from the maximum amount of memory in your system. After you subtract that memory from your physically addressable memory, you will have the portion that your OS and Applications share.

If you need to extend the amount of RAM your apps have access to, there is a switch that can be set in boot.ini, but this can constrain the amount of memory windows has to work with.

Tim Slattery did a good article on windows ram usage.

There is a great explanation of the page file's importance and usage in response to this serverfault question.

To gain more usable memory your best bet is to upgrade to a 64-bit OS which will be able to make use of a full 3.5+ gigs of RAM.

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Is there a tool to list how much RAM is still left after all the drivers and other things have taken their toll? – Aaron Digulla Nov 10 '09 at 17:16
Okay, I checked the memory map. The device manager says that I have 3.3GB RAM available which means 0.8GB are missing. Any ideas? – Aaron Digulla Nov 17 '09 at 9:07

Firstly, I'd change your swapfile from a tiny fixed one to system managed. Windows is trying to help you and you keep stopping it.

The other point is have you tried testing your RAM chips? Could be you start seeing these effects at around 2.5GB because one of your RAM chips is faulty and you start hitting the problem chip around then.

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I doubt that all 4 systems have the same hardware error. – foraidt Nov 11 '09 at 8:47
Ah yes, missed that, thought it was just one PC. – GAThrawn Nov 11 '09 at 13:21

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