A/UX on new 030 notebooks?

[Paul Campbell]

In article <7941 at segue.segue.com> gene at segue.segue.com (Gene Hightower) writes:
>
>If A/UX was important to Apple you would see 68851 sockets in LCs and
>maybe CMOS versions of the 68010 in the portable with some type of low
>power MMU.
>
>Unix can run on 68010 systems.  Look at the old Sun-1 and Sun-2
>workstations.

No! - the old Sun MMUs use LOTS of power hungry SRAM - not something you pop
in a portable, and the 68451 (the Mot. MMU) is very tacky (hard to program
well) and also very slow. Chances are you will end up finding that a CMOS '030
is lower power than a CMOS '010 plus an SRAM MMU. Also the '010 only has a
16MB address space (small programs only please, no 32-bit Mac world). Finally
you are talking about a rewrite of a VERY large part of the A/UX kernel for
a new MMU probably not something anyone at Apple's going to look on as  
a high priority compared with doing the work for '040s (easier), 7.0 and
future Unix release support (ie V.4 or some such).

>I don't design hardware and so I don't claim to be an expert, but in
>the case of the LC I don't think that adding support for the 68851
>would have been a big deal.

Actually it is since the addressing path must pass through the PMMU,
unlike an FPU where it is just tacked onto the bus you can't have something
with a PMMU that unplugs without having something that plugs into the
PMMU socket in it's place - this also means you have to have the socket on
main CPU board (you can't add it to an external board). Also I don't think
that they make anything in a PMMU that is pluggable that isn't a ceramic
PGA (which in hardware terms means expensive and physically big). Adding a PMMU
also slows an '020 down. Finally the volumes for PMMUs these days must be very
low - everybody is using '030s and '040s which means that the prices aren't
going to get any cheaper.

My guess is that a '020 + PGA socket + dummy chip + board space probably
costs more than an '030. So what the people at Apple were really deciding
was "is the added cost of an '030 worth the added functionality in this low
end machine" (where the added functionality is 7.0 VM + A/UX)

Also rumor has it that the 'LC was a 'pirate project' that was just about done
when they decided to concentrate on low-end machines - chances are they just
took what was done and decided to ship it ...

	Paul

-- 
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