Re: using more than 2 GB as a ram disk

H. Peter Anvin (hpa@transmeta.com)
3 Feb 1999 23:22:47 GMT

Followup to: <199902031830.NAA09100@saturn.cs.uml.edu>
By author: "Albert D. Cahalan" <acahalan@cs.uml.edu>
In newsgroup: linux.dev.kernel
>
> The compiler must be hacked to use a 64-bit model, with pointers
> normallized. The low 32 bits of a pointer would only hold 23 bits
> of the address space; the other 13 bits are the segment. This hack
> was fairly common for DOS software, not something I dreamed up.
>
> Yeah, this is slow. Every memory access needs a segment override.
> The job gets done though: true flat-memory 64-bit software on ia32.
>

Hardly "true flat-memory 64-bit"; it is a hacked 36-bit model where
you either store pointers in a non-flat format or normalize them every
time; once (or if) Intel adds more adds more address bits than 36
you're hosed again.

Not to mention the cost to load segments for every reference.

-hpa

-- 
"Linux is a very complete and sophisticated operating system.  There
are, and will be, large numbers of applications available for it."
    -- Paul Maritz, Group Vice President for Platforms And Applications,
       Microsoft Corporation [Reference at: http://www.kernel.org/~hpa/ms.html]


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