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From: ruiu@tic.UUCP
Newsgroups: comp.dcom.lans,comp.sys.ibm.pc
Subject: Re: IBM PC/AT DMA loses (was Re: PC LAN Comparison)
Message-ID: <162@tic.UUCP>
Date: Wed, 25-Nov-87 00:07:42 EST
Article-I.D.: tic.162
Posted: Wed Nov 25 00:07:42 1987
Date-Received: Sun, 29-Nov-87 02:02:30 EST
References: <2070@killer.UUCP> <1020@kodak.UUCP> <155@tic.UUCP> <261@kaos.UUCP> <1560@cup.portal.com>
Organization: U of A, E.E., Edmonton,Canada
Lines: 27
Xref: utgpu comp.dcom.lans:865 comp.sys.ibm.pc:8999
Summary: All this seems to make the dual ported approach more sensible.


[The discussion is about why DMA would be slower on an AT than polled I/O]

In light of the facts pointed out by everyone, a poor implementation of DMA
seems to be available on the AT. A certain traditionalist streak in me refuses
to accept a tight loop as the highest performance data transfers.

So if DMA is no good, then what is the high performance approach needed to
'squeeze' every ounce of performance out of an AT ?

An aquaintance who is designing a major PC based hardware project has chosen
to use double-ported memory. Truett Smith has already suggested this as the 
solution.

So, in light of the dropping cost of such devices, they are the preferred way
to go. Right ?

Does anyone care to comment? Does anyone know of any products that use this
approach to data transfers ?

(What did I start with that innocuous first posting ??!!? :-)

-- 
Dragos Ruiu          Disclaimer: My opinons are my employer's, I'm unemployed!
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(403) 432-0090         #1705, 8515 112th Street, Edmonton, Alta. Canada T6G 1K7 
Never play leapfrog with Unicorns...