2 Jun
2014
2 Jun
'14
8:37 p.m.
On Mon, Jun 2, 2014 at 10:24 AM, John Cowan <cowan(a)mercury.ccil.org> wrote:
The original Mac 128K was a 68000 processor, and IIRC
memory protection
didn't arrive until the 68020.
Sort of. Did not arrive to >>Apple<< until the '020 based Mac-II.
Les Crudele (one the 68k's designers) tells a great story about this. The
original device had a PDP-11 base/limit register MMU as an external chip
who's number I forget (and could not do demand paging by itself -- Masscomp
and Apollo would use 2 of them and build their own MMU). According to
Les, Moto offered to give Apple the MMU chip at a substantial discount
(maybe even free) if they would use it for the Mac. But Jobs famously said
it was a personal computer and did not need it (remember the Alto's did not
have an MMU either).
Later, Moto would release the '010 which could do demanding paging with
help of an external MMU. The Stanford University Network Terminal (aka
"SUN" board) could use the '10. I don't think Apple did themselves,
but
my memory is that the was an after market '010 mod for some of the Macs.
At Masscomp, we retrofited the original CPU board to take a '010. In this
mode, the 'fixer' 68K and the '010 could run in parallel during a page
fault, which was slightly faster. But functionally, to the end user it
was the same as two 68K's. I'm not sure if Apollo did a retrofit.
Clem