Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!usc!neuro.usc.edu!annala
From: annala@neuro.usc.edu (A J Annala)
Newsgroups: comp.sys.ibm.pc
Subject: SOURCING:  IBM PC/AT Controller Using the 8237A DMA Controller
Message-ID: <22875@usc.edu>
Date: 14 Feb 90 09:06:35 GMT
Sender: news@usc.edu
Organization: University of Southern California, Los Angeles, CA
Lines: 13

There is a serious design defect in the IBM PC/AT that makes it very
difficult to use for real time data acquisition ... the fixed disk
controller was implemented using programmed i/o instead of DMA for
transfering data between memory and the hard disk drive.  The lack
of hardware DMA support for the hard disk means that if some other
DMA channel goes active (e.g. the 176.2 KHz parallel i/o channel on
my 8 channel digital audio tape deck) the 80286 processor is slowed
and the disk write request aborts.

I would really appreciate any advice you can offer about how to get
an IBM PC/AT hard disk controller that either uses DMA or has enough
internal memory buffering to be immune to the presence of another
active DMA channel.