Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!husc6!uwvax!astroatc!johnw
From: johnw@astroatc.UUCP (John F. Wardale)
Newsgroups: comp.arch
Subject: Re: The 360 was a design landmark  (360 vs vax)
Message-ID: <422@astroatc.UUCP>
Date: Tue, 25-Aug-87 15:54:28 EDT
Article-I.D.: astroatc.422
Posted: Tue Aug 25 15:54:28 1987
Date-Received: Fri, 28-Aug-87 05:11:50 EDT
References: <855@tjalk.cs.vu.nl> <2683@hoptoad.uucp> <916@haddock.ISC.COM> <418@astroatc.UUCP> <26444@sun.uucp>
Reply-To: johnw@astroatc.UUCP (John F. Wardale)
Organization: Astronautics Technology Cntr, Madison, WI
Lines: 47

In article <26444@sun.uucp> guy%gorodish@Sun.COM (Guy Harris) writes:
>> VAXen are falling by the wayside (despite DEC's best efforts)
>
>VAXes falling by the wayside?  I dunno about that, either.  DEC, VAXes, and VMS
>seem to be doing quite well for themselves.
Hoding, maybe....many "VAX-labs" are buying into non-DEC stuff
(MIPS, Sun, Pyramid, Sequent, et.al.)

>> is that 360's *CAN* be pipelined (tho not necessarily real easily) and
>> VAXen can't!  
>
>VAXes can't be pipelined?  Gee, I suspect some of the 8600's designers would be
>surprised to hear that.
The 8600 overlaps operand-decode with operand-fetch, and uses
multiple functional (execution) units, but **UNLIKE** IBM and any
other true pipe-line design, can *NOT* have multiple instructions
in the decode phase simultaniously!  
Why you ask?
Because the vax (unlike most others) encodes the instructions so
tightly that you can't find the next one until you're almost done
with the current one!!  This is due to operand-mode encoding,
the 200 some addressing, etc. etc. etc.

>> Top 370 designes top out at 20 MIPS (or is it more now?)
>> Top Vax design is maybe 8 MIPS.
>
>So?  By itself, that may merely indicate that DEC hasn't pushed raw hardware
>technology as hard as IBM has.
While the 370 is not nice, at least with it, the first
operand-byte **ALLWAYS** tells you where the next instruction
starts!  The vax could be *MUCH* faster if it did this too, but
then it would lose its code-density!

360:  designed for easy of implementation  (An idea common to RISC)
VAX:  designed for maximum code density    (Poor choise today!)
RISCs:designed for speed, thru simplicity

This is why a couple M$$ will buy a 20+ MIP IBM, or a sub-8 MIP
VAX, or gobs (20-80) of 10 MIP RISC-workstations  (Yes, this is
very much like comparing mopeds, pickup-trucks and 18-wheelers as
"cars", but it does show how design decisions effect speed!)

-- 
					John Wardale
... {seismo | harvard | ihnp4} ! {uwvax | cs.wisc.edu} ! astroatc!johnw

To err is human, to really foul up world news requires the net!