Path: utzoo!dptcdc!jarvis.csri.toronto.edu!mailrus!husc6!rutgers!apple!oliveb!amiga!cbmvax!daveh
From: daveh@cbmvax.UUCP (Dave Haynie)
Newsgroups: comp.sys.amiga
Subject: Re: UNIX vs. Amiga speeds
Message-ID: <6627@cbmvax.UUCP>
Date: 18 Apr 89 22:00:14 GMT
References: <626@xroads.UUCP>
Distribution: na
Organization: Commodore Technology, West Chester, PA
Lines: 41

in article <626@xroads.UUCP>, skipper@xroads.UUCP (Skipper Smith) says:
> Summary: That minor change
 
> By adding the 68010, the Amiga would have gained the capabilities
> to use virtual memory and create virtual machines.  For those who don't know
> what a virtual machine is, suffice to say that the problem (?) of running
> UNIX under AmigaDOS could have fairly easily (as a guess only, I am no expert
> on this topic) circumvented.  Oh yes, it is the MOVE.W SR,<ea> that causes
> that problem.  

Not really.  Virtual memory only works when you have an MMU of some sort.
While some instruction restart or continuation capability, as you get with
the 68010, is a necessary precondition to running a virtual memory system,
it's not sufficient on it's own to support such a system.

Running UNIX under AmigaOS, or visa-versa, is a much higher level problem
that dealing with condition codes.  For example, many aspects of AmigaOS
depend on the realtime response it delivers, which would disappear under
UNIX.  UNIX, on the other hand, requires things that would certainly trip
up AmigaOS's Exec.  And if you got UNIX working under AmigaOS somehow,
your UNIX would still be subject to crashes by errant AmigaOS programs.
To really get both working simultaneously, if it's even possible (eg, 
Dave != The Software Architect Of All This, I just build the hardware
that makes the discussion worthwhile), would probably require some kind
of superkernel that manages both operating systems.

> since I don't have 5-9 Mb of RAM to make it work reasonably well, but I would
> sure like to be able to use the unused portions of a 380 Mb hard drive (I got
> a good deal, ok?) for virtual memory until I can get that extra RAM.

If you have a 68020+68851 (like the A2620) or some 68030 system, this could be
done.  I'm not about to say it's easy, just possible.  Without an MMU of some
sort, forget it (an obvious conclusion if you really think about virtual 
memory and how it would have to work under the Amiga OS).

> Skipper Smith

-- 
Dave Haynie  "The 32 Bit Guy"     Commodore-Amiga  "The Crew That Never Rests"
   {uunet|pyramid|rutgers}!cbmvax!daveh      PLINK: D-DAVE H     BIX: hazy
              Amiga -- It's not just a job, it's an obsession