Alpha CPUs, was Re: [rescue] i860 Success

Patrick Giagnocavo +1.717.201.3366 patrick at
Mon May 3 22:06:49 CDT 2004

On Mon, May 03, 2004 at 06:55:25PM -0700, Francisco Javier Mesa-Martinez wrote:
> On Mon, 3 May 2004, Phil Stracchino wrote:
> > That coincides with my recollection that the first CPU Apple shipped
> > with virtual-memory capability was the 68020.
> I believe it was because Moto also offered the 68020 as a full chipset,
> including math coprocessor and MMU. Before that most people had to use the
> 68K with their own MMUs (like SUN). I believe that even with the 020 SUN
> used their own MMU (but I may be not correct there). The 020 was full
> 32bit adress, where the 68000 was 24bit real adress, but it used
> internally 32bits I believe, I dunno if this arrangement made the 68000
> hard to deal with. But at least it allowed any program to use 16MB which
> in the early 80s was a pretty big deal. I suppose that is why the original
> macOS came in 24 and 32bit modes.

Actually you are confusing a few things together.  

The original Mac shipped with a 68000.  Later Macs shipped with

A smart programmer wrote a tool which Apple bought and distributed for
free to everyone.  It was called Mode32.  Also some of the ROMs needed
to be cleaned up for later use - such ROMs that run properly are
called "32-bit clean".

The original MacOS would be the one that shipped with the first Macs;
they had no support for 32bit mode.  Later versions of the MacOS did
support 32bit mode - but the first Mac only supported 512K of RAM!

> Motorola seemed to have a much cleaner architecture, as they got the 68000
> out of the door with just 68000 transistors (and that is pretty neat for a
> system with 32bit registers), at least a lot of the alternative
> architectures from the 80s seemed to prefer Moto over intel. Atari, Amiga,
> Mac, SGI, SUN, NCR Tower, HP 9K et al all were based around Motorola CPUs.

I have heard it claimed (but have no experience to say) that the 68k
instruction set is more "orthogonal" than the x86's.

I remember running SunOS 4.something on a Sun3 box with a 68020.  It
was actually impressively fast at the time.


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