Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!wuarchive!zaphod.mps.ohio-state.edu!know!tegra!vail
From: vail@tegra.COM (Johnathan Vail)
Newsgroups: comp.periphs.scsi
Subject: Re: DOS/SCSI DMA?
Message-ID: <2154@atlas.tegra.COM>
Date: 12 Mar 91 17:11:27 GMT
References: <27080001@hplred.HP.COM>
Organization: Tegra-Varityper, Inc., Billerica, MA
Lines: 31
In-reply-to: piety@hplred.HP.COM's message of 11 Mar 91 16:08:39 GMT


In article <27080001@hplred.HP.COM> piety@hplred.HP.COM (Bob Piety) writes:

   Does anyone know of the availability of a driver that hooks into DOS
   and lets DOS and, hence, application programs communicate to a SCSI
   hard disk via DMA?

The DMA on an AT is much slower than the equivelent loop in software.
The DMA is there mostly for the refresh, I believe.  If DMA is used
then the bios for the disk would have the "driver" and DOS would still
wait for the IO to complete.

   It sure is sad to to see a high-performance 386 or 486 spinning its
   wheels while a disk head seeks to a given track.....

What *else* would a PC running DOS be doing?  DOS is not multitasking
and if a program is waiting for data from the disk then it waits for
that data.


Now if you were running unix....

jv


"Everything that gives us pleasure gives us pain to measure it by."
    -- The Residents, GOD IN THREE PERSONS
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|     | Johnathan Vail | n1dxg@tegra.com
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