Re: memory

Dominik Kubla (kubla@sundiver.zdv.uni-mainz.de)
Sat, 25 Apr 1998 01:09:10 +0200

On Fri, Apr 24, 1998 at 08:12:03PM +0300, Tuukka Toivonen wrote:
> On 23 Apr 1998, Frode Vatvedt Fjeld wrote:
>
> >I've been told the architecture [=x86] supports 64GB maximum.
>
> In fact, it's 64 terabytes (1 TB = 1024 GB).
> But this requires segmented memory model (16383 segments,
> each being 4 GB) and Unix (nor Linux) doesn't use segmentation.

Right with regard to Linux, wrong with regard to Unix in general:

1.) Every Unix implementation for the 80286 uses segmentation.
(eg. Xenix/286 or Coherent)

2.) Data General offers a version of DG/UX for its PPro SMP systems
which can address the whole 64 TB.

> Except that putting segments in a some kind of Unix kernel
> (like Linux) would be quite difficult, we would need also to
> swap complete 4 GB segments to get the full 4 TB memory
> space, which would be too slow for multitasking (IMO).

Why would we want to do this? We don't swap, Linux uses paging
which operates on pages, not segments. Unless you are saying that
the PMMU is strictly 32 bit. Wouldn't surprise me so, just look
how broken the overall design of the Intel architecture is.

Dominik Kubla

-- 
               "Waga hoshi wa doko ni tabine ya ama-no-gawa."
      In the Summer Evening, Where is My Star Hidden in the Milky Way?
                         Kobayashi Issa (1763-1828)


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