Newsgroups: comp.arch
Path: utzoo!henry
From: henry@zoo.toronto.edu (Henry Spencer)
Subject: Re: HPE Spectrum
Message-ID: <1990Oct14.002438.19524@zoo.toronto.edu>
Organization: U of Toronto Zoology
References: <123093@linus.mitre.org>
Date: Sun, 14 Oct 90 00:24:38 GMT

In article <123093@linus.mitre.org> jfjr@mbunix.mitre.org (Freedman) writes:
>I just learned about the HPE spectrum (64 bits address)
>in class...

Well, "64 bits address" after a fashion, in the same sense that the 8086
has 20-bit addresses or the pdp11/44 has 22-bit addresses (both of these
are normally considered 16-bit machines) or the RT has 40-bit addresses.
That is, you can change segment registers to map your *real* address space
to semi-arbitrary parts of a bigger space.  The trouble with this is that
if you start seriously exploiting it, it becomes a programming nightmare,
as any IBMPC programmer will tell you:  remapping is costly enough that it
cannot be made invisible, and so you run into abominations like having two
different kinds of pointers.
-- 
"...the i860 is a wonderful source     | Henry Spencer at U of Toronto Zoology
of thesis topics."    --Preston Briggs |  henry@zoo.toronto.edu   utzoo!henry