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From: jxw@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
Xref: watmath net.micro:12837 net.arch:2170


	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