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From: laser-lovers@ucbvax.UUCP
Newsgroups: mod.computers.laser-printers
Subject: Re: Fast PostScript engines
Message-ID: <8602210933.AA08055@uw-beaver.arpa>
Date: Fri, 21-Feb-86 04:33:17 EST
Article-I.D.: uw-beave.8602210933.AA08055
Posted: Fri Feb 21 04:33:17 1986
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> What is the bottleneck for printing large documents? Is it the 9600 baud
> RS232c or the hostcomputer speed? When using the Appletalk connection at
> some 100kbaud, isn't the 68000 the bottleneck?

I don't know a lot about the LaserWriter, but other people have commented
that generating bitmap fonts from the LW's internal form is probably a
major bottleneck, since this is a cpu-intensive process.  Also, see below.

> When you talk about processing overhead over drawing time, don't you think
> something like a hardware matrix mulitiplier like in an IRIS 2400
> workstation would speed up the whole thing?

You miss the point:  the problem is not complex calculations, but simple
decision overhead.  Determining what character is wanted, finding it in the
font, deciding where to place it in the bitmap.  A 68000 is not a Cray;
doing these things takes time.  On an 8 MHz 68000, a typical instruction
time is a couple of microseconds.  That adds up very quickly.  Decision
overhead is several hundred microseconds per character even in something
like Rob Pike's Blit terminal, which uses very simple fonts and has *no*
fancy transformations that would be helped by Iris-like hardware.

Note that this implies that a 9600-baud line is plenty fast enough if all
you are doing is sending characters to be drawn.  (Bitmaps are another
story, mind you!)  That's a character arriving about every millisecond,
which will be close to 100% cpu utilization in the printer even in the
very best case.

> Beside this all: do you know something about conversion software from
> PostScript to the QUIC language on QMS' LaserGrafix printers?...

Absolutely nothing, I fear.

				Henry Spencer @ U of Toronto Zoology
				{allegra,ihnp4,linus,decvax}!utzoo!henry