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From: truett@cup.portal.com
Newsgroups: comp.dcom.lans,comp.sys.ibm.pc
Subject: Re: IBM PC/AT DMA loses (was Re: PC LAN Comparison)
Message-ID: <1651@cup.portal.com>
Date: Sat, 28-Nov-87 03:35:54 EST
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Posted: Sat Nov 28 03:35:54 1987
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rulu@tic.uucp (Dragos Rulu) asks if there are any examples of commercial
hardware products that use the dual-ported memory approach to bulk data
movement into and out of an IBM PC/AT.  There are many, but let me illustrate
the preponderance of this method by looking at one situation where bulk data
must be moved quite quickly -- laser printer interfaces.

I know of at least four such interfaces that use some form of memory dual-
porting to achieve high transfer rates:  1) the Tall Tree JLaser, 2) the
Advanced Vision Research MegaBuffer, 3) the Cordata LBP interface, and
4) the AST Turbolaser interface.  I believe the Laser Master also does this.
Unfortunately, I am not very familiar with the Hewlitt-Packard LaserJet
interfaces.  This problem of moving data to a fast printing engine quickly
becomes most acute when bit-mapped graphics are involved.

Why all of the laser printer manuafacturers haven't come out with a SCSI
interface is beyond me!  It has the throughput and would allow the printer
interface to share a slot with other peripherals.  Similar considerations

would apply to input from image scanners.  This surfeit of proprietary
interfaces cannot be any good, in the long run, for the industry.  I would
note that most SCSI interfaces for the PC standard bus give the programmer
the choice of DMA or PIO control of the transfer.

Truett Smith, Sunnyvale, CA
UUCP:  truett@cup.portal.com