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hi I am having winxp professional 32bit edition in my laptop which is having 4GB . how can I know how much memory using by WINXP OS. I heard that WINXP 32 bit will not support 4GB RAM meanse It will use only 3GB rather than we are 4GB also.

Can you tellme how to utilise the 4 gB RAM

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3 Answers

There's a common confusion about memory use in 32 bit Windows. Leaving aside the 3GB switch for the moment, any individual process can only use 2GB of memory. This is because the Windows virtual memory manager maps the top 2GB of the process's address space to system memory. However all the 4GB can be used by Windows, so if you have two processes they can simultaneously use 2GB each (less a bit for Windows and other processes). You don't need to do anything special to make use of the whole 4GB of memory.

The 3GB switch modifies the way Windows handles virtual memory so it maps only the top 1GB of a process's address space to system memory. This means a single process can use up 3GB of RAM. However unless you have a single process that needs above 2GB RAM you won't have achieved anything except to make Windows as a while slightly slower.

Note that most PC BIOSes reserve bits of memory so you may find Windows can only see 3 and a bit of the 4GB you have installed. If so this is a hardware issue not a Windows problem and there isn't much you can do about it.


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I don't think he's talking about 3GB switch, nor is he asking about virtual memory space. I think he's just asking about using all 4GB of RAM on a 32bit operating system. This is quite impossible without "tricks" like PAE which are only supported (for increasing memory) on Windows Server versions. This isn't a BIOS issue, it's an address space issue. Every component needs to be addressable if you're going to talk to it. The limiting factor here is address space; 2^32 = 4GB and you're right, there's nothing that can be done about it. –  Boden Jun 22 '09 at 15:37
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Jeff Atwood has a blog post about having 4 Gb of RAM in 32bit Windows.

Dude, Where's My 4 Gigabytes of RAM?

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Upgrade to a 64-bits version of XP. :-) Actually, most 32-bits applications will work on a 64-bits system. Am not sure if your laptop can handle a 64-bits OS, but if it can then it should be able to use more of your memory. About the /3GB setting that you can add to your boot.ini, it's useless unless your applications support this option too. They need to be compiled with the /LARGEADDRESSAWARE flag set. Then there's the Physical Address Extension, which is an Intel technique to extend the memory from 32 to 36 bits, thus you could have up to 64 GB of RAM. But again, applicaations need to be developed to support this, else it's of no use.

Btw, Windows does use the 4 GB that you have. It just doesn't provide this memory to your applications. Applications can normally use up to 2 GB of RAM. Windows won't be able to use more than 4 GB, unless you use a 64-bits Windows version or use PAE to extend memory to 64 GB.

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Typical applications (e.g. non-drivers) do not need to be aware of PAE like they do /3GB. PAE is implemented by the OS memory manager and applications don't need to know about it. –  Boden Jun 22 '09 at 15:44
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