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From: j...@fas.ri.cmu.edu (John Willis)
Newsgroups: net.micro,net.arch
Subject: Re: What if IBM used a 68000
Message-ID: <212@fas.ri.cmu.edu>
Date: Sat, 23-Nov-85 00:58:09 EST
Article-I.D.: fas.212
Posted: Sat Nov 23 00:58:09 1985
Date-Received: Mon, 25-Nov-85 08:02:16 EST
Organization: Carnegie-Mellon University, CS/RI
Lines: 44
But wait...
IBM tried workstations around both the 8088 and 68000. While
the Entry System division was designing the PC, IBM Instruments was
developing the 9000 family around the 68000. Both were initially given
the kind of strong marketing support IBM is famous for. Customers
cast an economic vote for the 8088, not the 68000.
I believe that there were good technical reasons...
* Ignoring the abortive 68451, Motorola did not even
produced an external VLSI MMU until 1985 (does it work
even now ?). When it came time to put XENIX on the
9000, a separate board full of LSI was required,
substantially driving up the cost. The 8088 came with
MMU on board.
* Virtual memory support (through the MMU) required an
awkward probing of each page with the 68000 in order
to avoid having to use two processors for each system.
It took the 68010 to make demand paging a real
possibility.
* The Motorola addressing scheme lead to use of Motorola's
Versabus in an effort to support an outside standard.
Versabus was far more complex and expensive to support
than the "proprietary" PC bus. Carrying a sixteen bit
data path through out the machine led to a planar board
nearly 17" square.
* Motorola did not have a real VLSI floating point
processor, leading IBM to OEM the SKY Versabus FPU
board. For ~7K$, the consumer got perhaps five
times the performance of a 150$ 8087. Without the
accelerator, the 68000 was substantially slower on
floating point than the 8088 / 8087. (Newer SKY
boards now provided higher bang / buck.)
The 68000 had it's chance, with some of the best effort IBM
could put behind it, and failed to make the impact the PC has for
numerous, solid technical reasons.
-John
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From: hamm...@petrus.UUCP (Rich A. Hammond)
Newsgroups: net.micro,net.arch
Subject: Re: What if IBM used a 68000
Message-ID: <702@petrus.UUCP>
Date: Tue, 26-Nov-85 07:16:04 EST
Article-I.D.: petrus.702
Posted: Tue Nov 26 07:16:04 1985
Date-Received: Wed, 27-Nov-85 05:48:14 EST
References: <212@fas.ri.cmu.edu>
Organization: Bell Communications Research, Inc
Lines: 39
> IBM tried workstations around both the 8088 and 68000. While
> ... Customers cast an economic vote for the 8088, not the 68000.
>
> I believe that there were good technical reasons...
>
Re: MMU - the 68451 is at least as good as 8088's on board MMU
besides, it is quite possible to write position ind. code
with a 68000. (i.e. no MMU required)
Re: Virtual Memory - the 8088 can handle page faults? No way!
Faulting on segment sized (64k) objects in a 256k
memory is pretty silly.
Re: Addressing scheme - Motorola's addressing scheme does not
force one to do anything in particular. The use of the
Versabus was probably to pick up some exisiting boards
(A/D, ... maybe?). A sixteen bit data path isn't all
that expensive, remember, both systems have a 20 bit plus
address bus. 20 + 8 vs 20 +16
Re: 8087 support vs Motorola. I don't believe early PC's came
with an 8087, by the time the 8087 could have been
a factor PC's were already well established. Most software
ported from CP/M systems didn't use 8087's.
>
> The 68000 had it's chance, with some of the best effort IBM
> could put behind it, and failed to make the impact the PC has for
> numerous, solid technical reasons.
>
> -John
One other point, which you don't mention, but many do. The 68000 supports
8 bit peripherals (6800 family chips) with CPU generated E, VMA', VPA'
and with instructions (Move Peripheral Data). The 6800 family chips
include a nice video display controller, UART, ... As far as I can see,
the claim that an 8088 supports 8 bit stuff better is pure baloney.
You fail to convince me that the reasons are technical, or solid.
I don't believe that the 68000 had the best effort behind it, marketing
wise, and it was certainly aimed at a different environment than a PC.
Rich Hammond {ucbvax|allegra|decvax|ihnp4} !bellcore!hammond
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From: grunw...@uiucdcsb.CS.UIUC.EDU
Newsgroups: net.micro
Subject: Re: What if IBM used a 68000
Message-ID: <4400133@uiucdcsb>
Date: Wed, 27-Nov-85 14:00:00 EST
Article-I.D.: uiucdcsb.4400133
Posted: Wed Nov 27 14:00:00 1985
Date-Received: Sat, 30-Nov-85 06:32:31 EST
References: <212@fas.ri.cmu.edu>
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Nf-From: uiucdcsb.CS.UIUC.EDU!grunwald Nov 27 13:00:00 1985
anyway, if it's politics, why did IBM produce the IBM-PC/370 using re-micro-
coded 68000's?
clearly, that means that the vast powers & buckeroos of IBM were able to be
brought to bear on Motorola to allow IBM to have access to the mask-set.
Clearly, IBM wasn't going to simply contract the job out & let Motorola
make 370's-on-a-chip to sell to everyone.
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From: he...@utzoo.UUCP (Henry Spencer)
Newsgroups: net.micro,net.arch
Subject: Re: What if IBM used a 68000
Message-ID: <6178@utzoo.UUCP>
Date: Wed, 27-Nov-85 17:45:59 EST
Article-I.D.: utzoo.6178
Posted: Wed Nov 27 17:45:59 1985
Date-Received: Wed, 27-Nov-85 17:45:59 EST
References: <212@fas.ri.cmu.edu>, <702@petrus.UUCP>
Organization: U of Toronto Zoology
Lines: 13
> besides, it is quite possible to write position ind. code
> with a 68000. (i.e. no MMU required)
Try writing the code for position-independent pointers some time; it's lots
of fun, especially if you are never allowed to have a position-dependent
value around even for an instant (except in pre-agreed places like the A
registers). It's easy to write position-independent code if that code and
its data will *never* need to be moved once it starts running. Writing code
that can be moved at randomly-chosen times and continue to run is not
so simple.
--
Henry Spencer @ U of Toronto Zoology
{allegra,ihnp4,linus,decvax}!utzoo!henry
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From: j...@fas.ri.cmu.edu (John Willis)
Newsgroups: net.micro,net.arch
Subject: Re: What if IBM used a 68000
Message-ID: <213@fas.ri.cmu.edu>
Date: Thu, 28-Nov-85 16:03:15 EST
Article-I.D.: fas.213
Posted: Thu Nov 28 16:03:15 1985
Date-Received: Sat, 30-Nov-85 07:07:04 EST
References: <212@fas.ri.cmu.edu>, <142@heurikon.UUCP>
Organization: Carnegie-Mellon University, CS/RI
Lines: 22
* The 68451 may work now. After trying three
separate samples during the first year Motorola
tried to push them, we did not find one that
ran within reasonable temperature specs, let
along the published spec. Our software people
got disgusted well before Motorola final sold
us a running sample. Even within the spec,
the chip's translation time can easily be
improved on by LSI, take the SUN MMU for instance.
* Everyone's definition of an MMU is slightly
different, but the large number of XENIX systems
happily running on the 8088 suggest that their
scheme provides the basics for a UNIX system.
Try opening your mind to something beyond Motorola
hype.
* I wouldn't stoop to the level of character assasination
to support a point.
-John
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From: he...@utzoo.UUCP (Henry Spencer)
Newsgroups: net.micro
Subject: Re: What if IBM used a 68000
Message-ID: <6193@utzoo.UUCP>
Date: Sat, 30-Nov-85 20:31:19 EST
Article-I.D.: utzoo.6193
Posted: Sat Nov 30 20:31:19 1985
Date-Received: Sat, 30-Nov-85 20:31:19 EST
References: <212@fas.ri.cmu.edu>, <4400133@uiucdcsb>
Organization: U of Toronto Zoology
Lines: 15
> clearly, that means that the vast powers & buckeroos of IBM were able to be
> brought to bear on Motorola to allow IBM to have access to the mask-set.
> Clearly, IBM wasn't going to simply contract the job out & let Motorola
> make 370's-on-a-chip to sell to everyone.
It's not uncommon to contract such things out with a stipulation that the
result not be made available to anyone else. Quite possibly IBM did let
Motorola do the dirty work. This sort of deal is much more common than one
would think, because it's seldom publicized. For example, HP did not make
its own chips for its scientific pocket calculators in the early days (maybe
not even today, I'm not sure). They were done by outside contractors, under
ironclad confidentiality agreements.
--
Henry Spencer @ U of Toronto Zoology
{allegra,ihnp4,linus,decvax}!utzoo!henry