From: Foley, Brian (Galway) (Brian.P.Foley at domain compaq.com)
Date: Fri 29 Jun 2001 - 11:42:38 IST
From: kevin lyda [mailto:kevin at domain suberic.net]
> ibm *did* decide to mass market - they came up with the ibm pc.
> the original pc was ill-suited to run unix. my understanding was that
> there was no memory management unit on the 8088/8086 and no such thing
> as kernel mode on the chip. so you couldn't offer memory protection
> between processes. dos was about the best you could do (not surprising
> since it was based on the most widely used micro os of the time - cpm).
> otoh, the motorola 68k *did* offer a full set of features. the first
> sun workstation used them. but apple chose not to use those features in
> favor of a single-tasking computer. this later evolved into cooperative
> multi-tasking (baaaaad idea).
This one comes up every now and then, and I'm afraid it's not true.
Sure, the 8086 doesn't offer any MMU to let you do protected memory, but
there were plenty of UNIXes in the 80s that ran on raw 68000s. The 68000
could not support MMUs properly, as it lacked the support to correctly
'restart' a number of instructions if they were interrupted by page faults.
(This problem was fixed in the 68010 BTW, which was the CPU Sun used in
their earlier machines)
One of the other arguments usually used against UNIX on the original PCs is
that the first IBM PC only had 64K RAM. This conveniently ignores the fact
that there were UNIX implementations that ran on a PDP-11 with 128KB RAM
(and possibly even less, my memory is fuzzy here). Intestingly, like the
8086, the PDP-11 had 16-bit 'segments' of memory, so unless you went
fiddling with segment mappings, each process could only directly access 64K
code and 64K data at any one time...
Of course, the best argument is working code. So head over to
http://uzix.msx.org/ and have a look at a UNIX that runs on 8086s and Z80
based MSXes.
I think there was a discussion of this on alt.folklore.computers a couple of
years back too, but I can't remeber whether they said anything interesting
or not.
Cheers,
Brian.
-- "Oh my God, they killed Alpha!!! You bastards!" (Anonymous Alpha Engineer)
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