Re: large memory support for x86

From: Timur Tabi (
Date: Thu Oct 12 2000 - 13:54:25 EST

** Reply to message from Jeff Epler <> on Thu, 12 Oct 2000
13:08:19 -0500

> 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.

How about the kernel itself? How do I access the memory above 4GB inside a
device driver?

> 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
> yet.

Yes, it's ugly, but it works and it's compatible. Well, compatible with 32-bit
code, probably not compatible with Linux code overall.

Of course, you could define a pointer to be a 48-bit value, but I doubt that
would really work.

Timur Tabi -
Interactive Silicon -

When replying to a mailing-list message, please don't cc: me, because then I'll just get two copies of the same message. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to Please read the FAQ at

This archive was generated by hypermail 2b29 : Sun Oct 15 2000 - 21:00:23 EST