Path: utzoo!utgpu!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!bloom-beacon!gatech!purdue!decwrl!mejac!gryphon!elroy!spl1!raj
From: raj@spl1.UUCP (Robert Alan Johnson)
Newsgroups: comp.sys.ibm.pc
Subject: 1:1 interleaving MFM controllers
Message-ID: <11272@spl1.UUCP>
Date: 4 Dec 88 00:49:41 GMT
Organization: The Software Public Library, Chicago, IL.
Lines: 30

I would like opinions on the best 1:1 controller for
MFM drives. 

There are a number of interesting issues I would like to
hear opinions about from qualified persons on the net.

ISSUE 1: NORTHGATE's contention that you can't do 1:1
on MFM drives.

ISSUE 2: Controller design approach.  I have recently looked
at the OMTI 1:1 MFM controller and discovered that they use
a PIO (Programmed I/O) approach which has a firmware routine
dispatching the characters from the controller.  When tested with
a 12MHz AT at 1:1 the throughput was awful.  We then tried again with a
20MHz AT.  Results were still bad.  When we discovered that we were running
in NON-TURBO mode.  When we kicked the 20MHz machine into TURBO, the
disk throughput went up to over 750KB/Second, blowing away a PS2/70 with
an ESDI drive!  It seems that the PIO design relies upon the CPU's 
power to get the high disk throughput.  The implication is that 1:1 is
wasted on 12MHz designs with this type of controller and that the
entire CPU would be sucked up during disk I/O being bad news for Windows,
XENIX, OS/2 and other software which attempts to overlap I/O and
other operations or multitask anything!  Aren't there DMA based
designs which can use local buffering and DMA to accomplish the same thing
without eating up the CPU?

Feedback much appreciated.
-- 
Robert A. Johnson, SysAdmin  {elroy,lll-winken,hombre,irs3,laidbak}!spl1!raj
The Software Public Library  VOICE: 1 312 248 5777