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I run many programs concurrently and require a lot of memory (ideally > 8 GB). It seems that the only way to do it (without buying more RAM) is to increase the pagefile.

However I can't seem to go past the 4096 MB limit (Windows XP) through the usual GUI way:

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Is there some internal Windows command to increase the pagefile size?

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Why do you need such a big pagefile? –  gronostaj Mar 9 '13 at 14:14
    
@gronostaj, I use programs that require a lot of memory like Photosho, multi-tab browsers, video viewers, etc –  Pacerier Mar 9 '13 at 14:22
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Virtual memory is much slower than RAM (I mean, like 250 times slower). I think you should upgrade physical RAM. –  gronostaj Mar 9 '13 at 14:30
    
@gronostaj, yes of course that's a better option, but it's more expensive. –  Pacerier Mar 9 '13 at 14:38
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@pts - The question is about Windows XP. Furthermore this question is about a Windows operating system not the Linux kernel. –  Ramhound Mar 9 '13 at 16:13

2 Answers 2

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A 32bit OS cannot address more than 4GB of RAM (i.e. 2 power 32). Therefore the pagefile cannot be bigger than 4GB. This is true for Linux and other OS' as well.

All applications loaded into memory will be loaded within the 4GB window. So even if you had 8GB of RAM in your machine you're stuck with 4GB of addressable RAM because of software limitations.

However, several versions of Windows (and other OS') are available that had support for Physical Address Extensions This was a CPU extension on 32bit processors that allowed utilising more than 4GB of RAM. It required support at the OS level as well. Note: you're still stuck with addressing 4GB of RAM at any one time, but the PAE feature allows you to switch that 4GB window to higher memory areas giving the ability to applications to access more RAM.

The problem with PAE is that it also needs application support for apps to use more memory. So an individual app still can't access more than 4GB of ram unless it's been written to utilise the Address Windowing Extensions

The link provided by Wayne's answer also requires PAE be turned on.

All in all, PAE is a cumbersome mechanism with limitations. Your best bet is to upgrade windows if you want to give more RAM. This will allow the OS to make better use of available RAM. However, be aware that your apps are 32bit and still have the 4GB memory limit (unless they use AWE). Windows will at least be able to swap them in and out of memory better than 32bit windows with PAE.

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This Microsoft article explains how to overcome the 4095 MB limit on paging file size. However, it begins by saying

When you set the paging file size in Windows, the documentation states that the largest paging file that you can select is 4,095 megabytes (MB). This limit is imposed by the page mapping that we use on x86 processors. These processors cannot handle more pages per page file.

Later it suggests that this may not be an effective solution and suggests adding more RAM.

Note that reading or writing a paging file of this size can be costly in terms of performance. If you find that you need a paging file of this size, it may be better to add more RAM to the computer.

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This is not actually quite accurately applied. See my answer below. –  Matt H Mar 11 '13 at 21:41

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