16 Jan
2007
16 Jan
'07
8:51 p.m.
On 16 Jan 2007 at 19:59, Roger Holmes wrote:
Well OK 5k dollars is not much, but in January the
following year for
10k, Apple's Lisa had several of the above, though I have to admit I
have seen some spectacular crashes as it was possible to corrupt the
sound buffers and also to seriously derange the CRT scanning. The
compiler generated some strange code to 'touch' the new top of stack
on subroutine entry so the OS could allocate all the extra space in
one go rather than in little bits. One enterprising British software
house even got Unix running on a Lisa with the (then) optional 5MB
profile hard disk. It wasn't C.A.P. but one of the other big ones of
the time.
The reason I mention this is because around 1981 I was working with
early steppings of the 80286. Microsoft had most of the code for
Xenix ported, but for the kernel--which they pretty much left to
Intel. Oddly, the system in the lab we were working with for our
own software was an Onyx box running, I think, V7 on a Z8000.
Consider how long it was after 1981 that the 80286 on the PeeCee
platform was running virtual memory tasks.
Doubtless the folks at Olivetti knew about the Onyx box and decided
to take a more modest approach and create a desktop "Personal
Computer".
The Lisa sold for twice the price of an M20 and contained quite a bit
more hardware. Categorizing the memory management as "virtual" is
perhaps stretching a term. A Lisa program had to "advise" the 68K
that it was going to use a physical address (i.e. you couldn't just
invent an address and use any old instruction to access it--
instructions on a single-CPU 68K weren't restartable after a fault).
So perhaps the memory was a bit more than "real physical" and less
than "virtual".
As an interesting aside, the operation I was with at about the same
time as the Lisa was being trotted out was looking to expand a bit
and needed something to supplement the VAX 11/750 that was our
workhorse. Since we didn't need another 750, I lobbied for a 730,
but one of the other founders lobbied hard for a Plexus 68K box. I
recall meeting with the Plexus sales guy and hearing him tell me that
they were working on virtual memory for their System III port. I
called him a liar and said that the 68000 was incapable of true VM.
I lost the battle and our firm bought the Plexus. It was an
incredibly slow waste of money.
For the M20's price point and market positioning, I really think that
an MMU would have been a waste of resources--and could well have been
a budget-buster.
Cheers,
Chuck