Newsgroups: bit.listserv.aix-l
Date:         Tue, 6 Oct 1992 13:29:00 EST
From:         "Peter C. Vernam" <pcv1584@MVS.DRAPER.COM>
Subject:      Re: help

Marcel Wijkstra AIO <wijkstra@fwi.uva.nl> writes:

>mmcglone@MGH.COM (Mike McGlone) writes:
>
>#a.) Has anyone compared a Sun (sparcstation 2) to their RS6000, and what
>swayed
>#your decision to the  RS6000.
>
>I just compared the PHIGS (a graphics standard for writing applications)
>capabilities of our RS/6000 model 730 running AIX 3.1.6, X11R3,
>graPHIGS 2.2.3 with two SPARCstations 2 (4/75) running SunOS 4.1.2,
>X11R5, PEX-SI.
>I wrote an iso-phigs program that runs on both systems almost without
>modifications, that implements a part of Lorensen's "Marching Cubes"
>algorithm (iso-surface generation from a 3D scalar valued array).
>(The reason I compared the RS/6000 with TWO Suns is, that PEX-SI is
>a layer on top of X-windows, which means that running a large PEX-SI program
>and the X-server on the same machine slows down both (since they are too
>big to fit into memory together in my case). The best thing to do was
>therefore to run the PEX-SI program on one and X on the other SPARC.)
>
>The RS/6000 was about 50% faster than a SPARC 2 on pure computational
>power (i.e. without any PHIGS calls included). When the complete program
>(i.e. including PHIGS routine calls) was run, the RS/6000 slowed down
>less than 7%, but the SPARC-combination took 140% more time for computing
>the iso-surface. Displaying the iso-surface was 680% slower on a SPARC than
>on the RS/6000...
>(When using one single SPARC 2, it was 7 times as slow as the RS/6000
>computing the iso-surface, and 14 times as slow displaying it.)
>
>No need to say I like the RS/6000 for its PHIGS implementation :-)

That's just about the most blatant case of comparing apples to oranges that
I've ever seen!!!  IBM's graPHIGS talks directly to the graphics hardware,
while MIT's PEX-SI uses the PEX protocol (an extension to the X protocol) to
talk to the PEX server process (an X server with the PEX extension).  The
advantage to the former is speed, the advantage to the latter is display
independence.

Also, PEX-SI is a PEX Sample Implementation -- it is not optimized for any
particular graphics hardware (as graPHIGS is) and, in fact, only works with
Sun's dumb frame buffers.  Therefore the graphics rendering is being done by
the SPARC CPU, which (even though you're using a completely separate machine)
is certainly not as fast for that purpose as IBM's custom graphics adapters
(by the way, you didn't specify which one you had on your RS/6000 -- I'm not
that familiar with the various RS/6000 model numbers).  If you ran SunPHIGS on
your SPARC with one of Sun's high-end graphics adapters (like the GT), you'd
get a fairer comparison, although I suspect the RS/6000 would still win
comfortably (at more than twice the cost; maybe MUCH more -- I can't find a
price for the 730).

I am not partial to Suns, nor a detractor of the RS/6000 (we have both here,
as well as DEC, SGI, HP, Apple, you-name-it), but let's be fair!


Peter Vernam                              Email: vernam@draper.com
Draper Laboratory, Inc.                   Voice: 617-258-2735
555 Technology Square                     Fax:   617-258-2705
Cambridge, MA 02139
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