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From: moore@PULSAR.FAC.CS.CMU.EDU (Dale Moore)
Newsgroups: comp.lang.postscript
Subject: ideas on onboard processors
Message-ID: <3068@pt.cs.cmu.edu>
Date: 21 Sep 88 16:50:46 GMT
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Organization: Carnegie-Mellon University, CS/RI
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Here are some of my thoughts about onboard vs outboard PostScript.

Outboard is the way most all PostScript printers work today.  The
processing is done out on the peripheral rather than in on the
general purpose processor.

Some folks concern is that the extra bandwidth necessary to ship the
image to the printer will be a bottleneck.  Ethernet and other mediums
operate at 10mps.  With a large number of vendors building hardware for
such networks, it is entirely feasible to build inexpensive Ethernet 
(rather than serial line or Appletalk) printer. Several folks have
already done so.  At an effective usage of 20% of the network bandwith,
300 dots per inch, 1 bit per dot, that comes down to less than 5 seconds
per page.  With the advent of FDDI and other networking technology, the
time necessary to ship that many bits over a standard cable will decrease.

Many of todays PostScript printers have more memory and faster CPU
inside the printer than the general purpose machine that is generating
the PostScript and sending it to the printer.  The analogy is that
the slave peripheral has more potential power than the master.
That is something that seems entirely backward to me.

Much of the time, a PostScipt printer (and its CPU and memory) are
sitting idle.  If the CPU and memory were available to the user
to perform other computing tasks when the printer was not in use,
this would result in a more effective use of the hardware.

Multi-Processors with multi-processing systems are commercially
available.  Sequent, Balance and Next are systems that produce
(or will shortly) commercial multi-processor systems.
The hardware that is typically devoted to the task of changing
page description languages into bitmaps could instead be part
of a multi-processor operating system.  Upon demand a single
processor could be devoted to doing its traditional task of turning
a page desciption language into bitmaps, and shipping those bitmaps
to the printer.  But when the printer was not needed for that task
the processor could be devoted to performing other tasks as a
normal part in the multi-processor system.

The time necessary to ship images to a printer will only decrease
as networking technology develops.   More effective use can be
made of the hardware if the hardware is part of a general purpose
system, rather than devoted to supporting a complex function
inside a peripheral.

Dale Moore
Computer Science
Carnegie Mellon University