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From: ebg@clsib21.UUCP (Ed Gordon)
Newsgroups: comp.arch
Subject: Re: D-machine helped spawn RISC
Message-ID: <551@clsib21.UUCP>
Date: Tue, 29-Sep-87 08:46:45 EDT
Article-I.D.: clsib21.551
Posted: Tue Sep 29 08:46:45 1987
Date-Received: Wed, 30-Sep-87 07:10:37 EDT
References: <347@erc3ba.UUCP> <478@esunix.UUCP> <2785@ames.arpa> <6266@apple.UUCP> <696@gumby.UUCP>
Organization: CLSI Inc., Newtonville, MA
Lines: 32
Summary: RISC and parallelism



Having never worked explicitly with the D machine, but having worked with
D machine graduates, and the Mini-D machine, I cannot claim to have explicit
knowledge of it's inner working.  But, if my knowledge does not fail me,
the D-machine, had a highly parallel, rather complicated parallel instruction
set, each made up of sub-instructions to handle the registers, alu, and
branch processing.  All of which was done in parallel for each instruction,
producing a fairly complex instruction, disregarding the simplistic nature
of the register set, which was understandable considering the nature
of the system.  The processor was essentially a microcontroller, with explicit
mechanisms for control of the bus.

I was also involved in the development of a "RISC"-like, pre-"RISC"
era processor, but I don't know what became of it.

If I understand the RISC architecture, it does not strive for parallelism,
but strives for a reduced instruction set, to simplify chip design, in order
to speed up execution times of instructions (one cycle per?).  The extent
of the effort was defined to me as an attempt to produce "assembler"
instructions, without the complications of (slow) HLL constructs,
not "firmware" instructions with explicit bus manipulation, as does the
Mini-D.  Comparing RISC's with the Mini-D, is like comparing "Apples" with
"Oranges", (or is that "Apples" with "Compaqs"?).  Do I misunderstand
the concept?

			--Ed Gordon
			--Data System Associates

"I know it's only rock and roll, and the opinions expressed are my own,
and are not necessarily those of any of the major recording studios, or
any other semi-coherent organization."