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From: steckel@alliant.UUCP (Geoff Steckel)
Newsgroups: comp.arch
Subject: Re: Word vs. Byte Orientation (really about nasty hardware)
Message-ID: <480@alliant.UUCP>
Date: Sat, 18-Apr-87 20:06:21 EST
Article-I.D.: alliant.480
Posted: Sat Apr 18 20:06:21 1987
Date-Received: Sun, 19-Apr-87 17:57:52 EST
References: <16122@amdcad.AMD.COM> <16125@amdcad.AMD.COM> <305@winchester.mips.UUCP> <16167@amdcad.AMD.COM> <7927@utzoo.UUCP>
Reply-To: steckel@alliant.UUCP (Geoff Steckel)
Distribution: na
Organization: Omnivore Technology, Newton, MA
Lines: 14
Keywords: word-addressing
Summary: New machines have to work with old boards

One point that I believe needs to be emphasized in the word-vs-byte discussion:

Many existing and useful boards (VME, Multibus I & (yuck) II, QBUS, etc, etc,
not excepting IBMPCbus) cannot be used except by a CPU with bus-level byte
addressing.  The life cycle cost of redesigning an entire system of peripherals
just to be able to use the newest CPU seems very high.  If I/O space is
separate from memory space, one can kluge some very clumsy fixes, but memory
mapped peripherals have problems...

Under my OS and I/O hat, I have quite a stock of horror stories about CPUs
with this problem.  Given the actual cost of CPUs vs peripherals, guess which
one got canned when the problems showed up?  Hint - we HAD to keep the
peripherals.
	Geoff Steckel (steckel@alliant.uucp, gwes@wjh12.uucp)