Path: utzoo!dptcdc!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!cs.utexas.edu!uunet!dg!mpogue
From: mpogue@dg.dg.com (Mike Pogue)
Newsgroups: comp.arch
Subject: Re: (graphics processor speedups)
Message-ID: <132@dg.dg.com>
Date: 18 Apr 89 13:06:56 GMT
References: <28930@apple.Apple.COM> <3300064@m.cs.uiuc.edu> <3880@ficc.uu.net> <7459@cadnetix.COM>
Reply-To: mpogue@dg.UUCP (Mike Pogue)
Organization: Data General, Westboro, MA.
Lines: 45

In article <7459@cadnetix.COM> beres@cadnetix.COM (Tim Beres) writes:
>
>In my opinion/guess, DEC went unaccelerated due to price reasons.  Likely
>wanted the best $$$/CPU MIP ratio at the time.  As someone from DEC pointed
>out, it wasn't due to the fact that a raw CPU is faster.  
>
>An interesting side-note:  It appears the future of microcoded graphics engines
>are over.  As well, general purpose graphics CPU's *appear* to be numbered.
>Gate-arrays to perform specific rendering tasks are the way to go.  This 
>statement is doused in gasoline - so flame away.
>
>				Tim
>

   Interestingly enough, we went through the same tradeoffs when we designed the
AViiON graphics subsystem.  We finally decided that it would costs just as much
to put in the circuitry to do the video refresh (e.g. 6845) as it would to put in
the uPD72120.

   With the uPD72120, we got the screen refresh along with a pretty fast drawing
engine for free!  If you haven't checked out this chip, from NEC, do so, because
it is cheap, fast, and does just about all you need it to do.

   For our COLOR AViiON, we needed something faster than the 72120 (which slowed
down with 8 planes of memory), and we wanted to very carefully control the 
POWER used (power costs money!!).  Therefore, we designed a custom array (about
25K gates) that took care of reducing power, as well as giving us the performance
we were looking for.

   We were able to design the gate array (using RISC techniques, incidentally)
to minimize bus bandwidth from CPU to GA, and we customized the array for X11
and Postscript support.

   I would agree that general purpose graphics processors hae their place, but
they are, in a sense, TOO flexible.  Future versions of the processor have to
start looking like a CPU (note that the i860 costs $750, and requires all kinds
of support chips, like static RAM, to take advantage of the speed).

   I like my graphics LEAN and MEAN.

   Mike Pogue
   Mngr, Graphics Workstations
   Data General Corp.

   My opinions are my own....