Path: utzoo!attcan!uunet!seismo!sundc!pitstop!sun!decwrl!labrea!rutgers!cs.utexas.edu!utastro!bigtex!james
From: james@bigtex.cactus.org (James Van Artsdalen)
Newsgroups: comp.sys.ibm.pc
Subject: Re: 1:1 interleaving MFM controllers
Message-ID: <11559@bigtex.cactus.org>
Date: 11 Dec 88 04:44:03 GMT
References: <11272@spl1.UUCP>
Reply-To: james@bigtex.cactus.org (James Van Artsdalen)
Organization: Institute of Applied Cosmology, Austin TX
Lines: 32

In <11272@spl1.UUCP>, raj@spl1.UUCP (Robert Alan Johnson) wrote:
> I would like opinions on the best 1:1 controller for
> MFM drives. 

WD1006/WA2 is a good bet.  Has floppy support too.

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

Nonsense.  If they can't get this right, don't buy anything from them.

> 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.

Yup.  DMA on a PC is much slower than "rep insw".  I don't know if
anyone at all uses DMA for disk access.

> 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!

Not necessarily true.  The controller reads the data into local memory
and then interrupts the CPU.  CPU then does "rep insw" and grabs it
all rather quickly: 6 clocks per word + I/O wait states.

We'll embarrass VAXen with raw CPU throughput, but never with I/O
bandwidth...
-- 
James R. Van Artsdalen		james@bigtex.cactus.org	  "Live Free or Die"
Dell Computer Corp, 9505 Arboretum Blvd Austin TX 78759		512-338-8789