Path: utzoo!attcan!uunet!dino!ux1.cso.uiuc.edu!ux1.cso.uiuc.edu!m.cs.uiuc.edu!sunc5!voss
From: voss@sunc5.cs.uiuc.edu
Newsgroups: comp.lang.smalltalk
Subject: Re: PPS R4 under OpenWindows?
Message-ID: <26900003@sunc5>
Date: 18 Sep 90 22:18:00 GMT
References: <174602@<1990Sep17>
Lines: 46
Nf-ID: #R:<1990Sep17:174602:sunc5:26900003:000:2490
Nf-From: sunc5.cs.uiuc.edu!voss    Sep 18 17:18:00 1990


> Can someone explain what is in the SPIM (St portable imaging model)?

As you should know, ST-80 is traditionally executed on a "virtual
machine" which (in theory) makes any supported machine look as though
it was specifically designed to run ST-80.

Basically, ParcPlace uses machine specific window systems to provide a
"virtual monitor" (they don't call it that).  You invoke ST-80 which
opens a window on the host, and then ST-80 treats that window as a
dedicated (normally mono) frame_buffer/monitor pair.  Inside the
window, PP ST-80 provides the traditional ST-80 windowed environment.

Except for differing screen sizes, the ST-80 graphics code can not
tell the difference between different machines.  ParcPlace also makes
a point of insuring that every SUN, MAC, ..... version A.B virtual
machine can use any other version A.B virtual machine's image.  Thus
if your ST-80 image will operate on any ParcPlace supported host, it
will (in theory) work on every ParcPlace host.  You can still write
non-portable code, the file-system is a standard problem.  However,
graphics are portable, self contained applications are portable, and
the host specific classes are explicitly isolated.

The cost of using a "virtual monitor" is the same as using a "virtual
machine" SPEED.  Obviously, writing directly to the hardware
frame_buffer is faster than going through a window system.  However,
by going through window systems ParcPlace can make someone else worry
about all the various flavors of graphics hardware.  This either cuts
their programming costs, increases the number of platforms supported,
or both.

I believe that ParcPlace uses the SunView windowing interface on Suns
at least in part because this is faster than X or NeWs when you are
specifying EVERY PIXEL.  The X and NeWs systems were both designed so
that clients could say things like (line from x1 y1 to x2 y2) instead
of (x1 y1 black, ..... xn yn black, ..... x2 y2 black).  X and NeWs
can support EVERY PIXEL mode, but SunView has less overhead.

The above is based on my experience with ParcPlace Smalltalk-80 over
the past three years.  I am currently using version 2.5 on a Sun 3/60.
I've never personally licensed PP ST-80, but I've convinced two
Universities to license it for me!
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Bill Voss -- Graduate Student -- University of Illinois at Urbana/Champaign