Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!mailrus!iuvax!watmath!grand!himacdonald
From: himacdonald@grand.waterloo.edu (Hamish Macdonald)
Newsgroups: comp.sys.amiga
Subject: Re: Questions about Harddisks
Message-ID: <32033@watmath.waterloo.edu>
Date: 28 Nov 89 13:48:54 GMT
References: <553@bmers58.UUCP>
Sender: daemon@watmath.waterloo.edu
Reply-To: himacdonald@grand.waterloo.edu (Hamish Macdonald)
Organization: U. of Waterloo, Ontario
Lines: 33

In article <553@bmers58.UUCP> keithh@atreus.UUCP (Keith Hanlan) writes:
>I'm putting together an A2000 machine...
>...
>o DMA vs non-DMA
>	I'm almost ready to give up. I continue to read conflicting
>	optinions about DMA vs non-DMA hard-disk controllers. My gut
>	opinion is that DMA is a more elegant solution that off-loads the
>	CPU and hence doesn't degrade the machine as much. Am I right?
>	Then why does anybody build non-DMA? Why do they claim such
>	remarkable through-put with some non-DMA drives? And finally,
>	what the heck is the "quasi" DMA and "true" DMA I occassionally 
>	hear about.
>...
>Thank you,
>Keith Hanlan
>Bell-Northern Research
>utgpu!bnr-vpa!bnr-fos!bmers58!keithh%atreus or keithh@bnr.ca

In effect you are correct.  They sell non-DMA controllers because people
will buy them...  and because they are cheaper to build/buy.

A lot of the non-DMA controllers probably do get remarkable
throughput, but the point is, you can't do anything else with your CPU
while you are getting this remarkable throughput. A DMA controller
lets your CPU do other stuff while reading the disk.

Don't know about 'quasi' DMA.

Hamish.
----------------------------------------------------------------
Hamish Macdonald.
himacdonald@grand                       watmath!grand!himacdonald
himacdonald@grand.uwaterloo.ca     himacdonald@grand.waterloo.edu