來源︰
http://forums11.itrc.hp.com/service/forums/questionanswer.do?admit=10944...

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A 32bit Linux system can access up to 64GB of memory (assuming the mainboard is capable of having that amount).

You have to make sure the kernel you are using is also compiled to take advantage of such amounts of memory.

In the RHEL4 series, you're standard kernel and kernel-smp packages can only address 4GB of memory.

If you have more than 4, then you use the smp enabled kernel-hugemem packages.

All this being said, an individual process can only access 3GB of memory (each).

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32bits is 4GB limit yes. But for a long time now, there is the PAE extension in 32bits CPU, allowing the memory allocation to be done on 36bits.
So with PAE, it's 64GB. PAE is part of the 'bigmem' kernel option. So almost kernel have it and can use more than 4GB in 32bits.
Restriction is from chipset for Linux.

Windows is different, using PAE is not automatic and can occurs in software issues with drivers for exemple. It is one thing where Linux is better.

You may also read:
http://www.linux.com/archive/feature/119287