Re: large memory support for x86

From: Jeff Epler (
Date: Thu Oct 12 2000 - 13:08:19 EST

On Thu, Oct 12, 2000 at 10:36:38AM -0700, Kiril Vidimce wrote:
> Allocate = malloc(). The process needs to be able to operate on >4 GB
> chunks of memory. I understand that it's only a 32 bit address space
> which is why I was surprised when I read that Linux 2.4.x will support
> upwards of 64 GB's of memory.
> Thanks for all the responses.

Pointers are still 32 bits on x86, and the visible address space for
any particular process is still somewhat less than 4G.

I believe that if you select Linux on Alpha that you can have more than 4G
per process, but that may or may not be true.

What the support for >4G of memory on x86 is about, is the "PAE", Page Address
Extension, supported on P6 generation of machines, as well as on Athlons
(I think). With these, the kernel can use >4G of memory, but it still can't
present a >32bit address space to user processes. But you could have 8G
physical RAM and run 4 ~2G or 2 ~4G processes simultaneously in core.

There may or may not be some way to support an abomination like the old "far"
pointers in DOS (multiple 4G segments), but I don't think it has been written

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