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From: casey@admin.cognet.ucla.edu (Casey Leedom)
Newsgroups: comp.sys.next
Subject: Re: blasting bitmaps (was Re: How did they make the printer so cheap?)
Message-ID: <17012@shemp.CS.UCLA.EDU>
Date: 20 Oct 88 08:09:29 GMT
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| From: spolsky-joel@CS.YALE.EDU (Joel Spolsky)
| 
| I have a dumb question.  Why does anybody bother to send complete bitmaps
| to laser printers, especially 2M bitmaps?  Wouldn't it be trivial to
| compress them for transmission using ZLW or such?  I'll bet you could get
| 90% compression or more for plain text.  Surely the time saved in
| transmission would pay for the compression time, especially if
| compression is implemented in hardware.  Not to mention the savings in
| ethernet traffic on networks. 

  Someone said earlier that the NeXT lpr transfers PostScript across the
net, not bitmaps.

  Compressing the data stream to the laser printer would require that
significantly complex hardware be put into the printer.  This would in
turn drive up the cost of the printer.  At 300dpi the NeXT sends data to
the printer at 1.8mbps and at 400dpi it transmits at 3.2mbps [1].  The
fact that it transmits faster at the higher density indicates that the
printing process is printer engine bound rather than data transfer bound.
A quick check shows:

	300dpi:	300x300 bits/inch^2 / 1.8e6 bits/second
		== 5e-2 seconds/inch^2

	400dpi:	400x400 bits/inch/inch / 3.2e6 bits/second
		== 5e-2 seconds/inch^2

At a conservative 8.5 x 11 inch^2 / page (the whole page is not really
printable, but I've forgotten what the minimum border is), this gives us

	8.5 x 11 inch^2 x 5e-2 seconds/inch^2
	== 4.675 seconds/page
	== 12.834 pages/minute

I think the minimum border is something like 1/4 inch which gives a more
realistic 4.2 seconds/page == 14.286 pages/minute.

Casey

[1]	First Impressions - The NeXT Computer; Tom Thompson, Nick Baran;
	BYTE BIX, October 15, 1988

--------
The problems and issues are complex and inextricably linked: the national
deficit, defense spending, foreign policy, the foreign trade deficit, the
environment, homelessness, affordable health care, ...  No simple answer
will suffice.  And yet Bush claims that things are fine and can be left
as is.  Where has he been for the last eight years???  Disneyland?