From: John P. Looney (john at domain antefacto.com)
Date: Fri 29 Jun 2001 - 13:56:38 IST
On Fri, Jun 29, 2001 at 11:36:11AM +0000, David Golden mentioned:
> The 68000 could have memory protection, but in the form of an extra chip,
> the 68851 - the Apple Lisa had one, but cost a small fortune. When no-one
> bought the Lisa, Apple produced a cut-down version - the Mac...
> The 68030 and above had on-board MMUs, except in the "EC" forms
> (embedded controls tend not to use them).
The 68851 wasn't made till 1985 or so. Before then, companies like sun
that needed an MMU on a 68000 based box had to use a second 68000 to be
the MMU - this is actually how the first Sun workstation worked. A
complete 68000 that was just acting as an MMU.
> The amiga (1985) used the 68000 for pre-emptive multitasking, but with
> cooperative memory protection (via semaphore locking). I always found
> that my Amiga, without true memory protection, was more stable than a
> windows pc, ostensibly with memory protection... When I later got an
> amiga cpu card with an MMU, I promptly stuck linux/m68k on it... :-)
Ah. You didn't do much development then. Ooops, I wrote to a null
pointer, and crashed my machine. Ooops. I've written into the wrong area
of RAM, over my memory-mapped floppy driver control ports, and killed the
floppy. Oooops, that hack I downloaded from the net's just started writing
to wierd places, and now everything is messed up.
> Given that the A3000 was price- and performance- competitive (and
> superior for gfx and sound) with high-end PCs of the day, history could
> have been bery different, if CBM management hadn't been such complete
I wouldn't go that far. It was priced at 3000UKP. About the same as the
486DX2s that were just out...but twice as fast, on the clock speed front.
The A3000+ - now that was a different story.
-- When I say 'free', I mean 'free': free from bond, of chain or command: to go where you will, even to Mordor, Saruman, if you desire. " -- Gandalf, paraphrasing the choice between Free and Non-free software
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