From: billk@sr.hp.com (Bill Katz)
Newsgroups: alt.folklore.computers,comp.arch
Subject: Re: why 8088? [was: Re: A primeval C compiler]
Date: 9 Aug 1999 05:00:38 GMT

Paul DeMone (pdemone@igs.net) wrote:


: Rob Nicholson wrote:
: >
: > >    It wouldn't be the 6809 since that part could still only address
: > >    64K.  This was a primary selection criterion that ruled out
: > >    virtually all 8 bitters.
: >
: > 68008 would have been a nicer choice. Then we would never have had any of
: > that FAR larking about :-) Jeez - those memory models in Borland C made my
: > head hurt.

In his book _Interfacing to the IBM Personal Computer_ (Sams, 1990)
Lewis C. Eggebrecht states:

"As the architect and design team leader for the IBM PC project,
I am often asked why the 8088 microprocessor was selected for the
original PC"

To paraphrase:

IBM proprietary chips ruled out because of high cost, and the lack
of self-hosted development tools. "You needed an IBM mainframe to do
software development, which was somewhat beyond the target developer's means".

6502 ruled out because "the last thing IBM wanted was to be viewed
as an Apple-compatible manufacturer.

Z80 ruled out as IBM would be seen as a follower, 64kaddress space
wasn't enough, Z8000 had a totally different architecture, so there wasn't
a good migration path.

68000 was carefully considered.  "AN excellent architecture chip, it has
proven to be a worthy competitor to the Intel-based architecture."
there wer four major concerns:

1) 16 bit data path would require more bus buffers, therefore a more
	expensive system board.

2) more memory chips for a minimum configuration.

3) while it had a performance advantage, the 68000 was not as memory
	efficient.

4) Companion and support chips not as well covered as Intel.o

He also felt the the 68000 didn't have as good software and support tools,
and the similar register model allowed the porting of 8080 tools
to the 8086/8088.

"In summary the 8088 was selected because it allowed the lowest
cost implementation of an architecture that provided a migration path to a
larger address space and higher performance implementations.  Because
it was a unique choice relative to competitive system implementations, IBM
could be viewed as a leader, rather than a follower.  It had a feasible
software migration path that allowed access to the large base of existing
8080 software.  The 8088 was a comfortable solution for IBM.  Was it the
best processor architecture available at the time? Probably not, but history
seems to have been kind to the decision."


#MY OPINION MODE ON

I often wondered when dealing with PCs how much farther ahead we would
have been if IBM had chosen the 68000, and we wouldn't have collectively
wasted millions of man years futzing with silly 64k segments and
the 640k limit.  Granted a 68000 design would have probably had an 8,12,
or 15M limit, but it would have taken many more years to run into it.

	-Bill Katz

My opinions are not those of Hewlett-Packard (or Agilent Technologies).

From: mash@mash.engr.sgi.com (John R. Mashey)
Newsgroups: alt.folklore.computers,comp.arch
Subject: Re: why 8088? [was: Re: A primeval C compiler]
Date: 9 Aug 1999 22:37:53 GMT

In article <7oln9m$g1u@canyon.sr.hp.com>, billk@sr.hp.com (Bill Katz) writes:

|> "As the architect and design team leader for the IBM PC project,
|> I am often asked why the 8088 microprocessor was selected for the
|> original PC"

This is the story I've always heard, but I've also heard of one more factor
that encouraged X86 over 68K,
from a reliable source, and it makes sense, and may even be
true, even if it usually doesn't get mentioned:

In dealing with external supplier, there would generally be one IBM
division that would be the lead in dealing with that supplier, and
if you were in another division, you had to work through that first division.
Needless to say, a fast-track effort like the IBM PC wouldn't care for that
much ... and there was already another division using 68Ks  ...

--
-john mashey    DISCLAIMER: <generic disclaimer: I speak for me only...>
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