How fast is a parallel port?

[Bill Stewart 908-949-0705 erebus.att.com!wcs]

I'm trying to find out how to connect big laser printers (50-100ppm)
to normal computers, in particular to 386/486 boxes running UNIX.
For a variety of ugly reasons, I don't want to use Ethernet -
I'd really like to use a parallel port.  But nobody I've talked to
knows how fast a parallel port can go on a typical machine, and
nobody's tried it at speeds over about 10ppm.

50-100 ppm is 1-2 pages/second, or typically 40-80 kilobits/second;
not much faster than a 38.4 kbps RS-232 port.
At least on our machines, and on the parallel port boards anyone
knew about, the Centronics driver was simple - the sender toggles a
lead when there's a byte to send, and the receiver toggles a lead
(causing hardware interrupt) after it reads it.  So the hardware guy
says "The port can go as fast as the software will handle interrupts."
After all, the traditional dot-matrix printer didn't need a whole
lot of CPU to feed it data, so there's no hardware assist.

Does anybody know how fast the typical 386/33 or 486 box running UNIX
can push data out the parallel port?  Has anybody tried it?
How much CPU does it burn?  Unfortunately, I don't have access to a
big printer to try it - is there some way to make a parallel port
READ data on UNIX?  DOS programs like LAPLINK or its equivalents can
get fairly high performance, but they're single-tasking programs
that can sit there and poll the hardware, rather than sharing a
multi-processing machine.

Are there any parallel port boards out there with hardware support
and/or DMA?  It wouldn't take much to do some simple buffering.

				Thanks;  Bill

P.S. Sorry about posting this twice; something's having trouble
doing cross-posting here, and I'm trying to concentrate followups to one place.
-- 
				Pray for peace;
					Bill
# Bill Stewart 908-949-0705 erebus.att.com!wcs AT&T Bell Labs 4M-312 Holmdel NJ
# "I can see all Southeast Asia, I can see El Salvador, ..."