Path: utzoo!mnetor!tmsoft!torsqnt!jarvis.csri.toronto.edu!rutgers!att!cbnews!wsd
From: wsd@cbnews.ATT.COM (wayne.s.dinsmore)
Newsgroups: comp.sys.ibm.pc
Subject: Re: RLL controllers & MFM disks
Summary: RLL overrides MFM
Keywords: RLL, MFM, Hard Disks
Message-ID: <9611@cbnews.ATT.COM>
Date: 19 Sep 89 12:01:21 GMT
References: <629@ccssrv.UUCP>
Reply-To: wsd@cbnews.ATT.COM (wayne.s.dinsmore,54265,an,4a118,508 691 3653)
Distribution: na
Organization: AT&T Bell Laboratories
Lines: 46

In article <629@ccssrv.UUCP> perry@ccssrv.UUCP (Perry Hutchison) writes:
-I can see why Seagate wouldn't want to warrant the _performance_ of a non-rll
-drive with an rll controller, but if it didn't work what's to prevent re-
                                                     ^^^^^^^^^^^^^^^^^^^^^
-formatting and using it with an mfm controller?  Surely the attempt at rll
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-isn't going to physically damage anything, is it?
-
-I can even less understand their objection to using an rll-rated drive with
-an mfm controller.
-
-Can anyone explain this?  Seagate, are you listening?

I have just the answer because of what I went through one weekend. Basically
it boils down to this: Rarely will a drive thats been formatted by an RLL
controller succumb to MFM formatting. 

I started with a 32MEG RLL drive on a hard card with an 8-bit controller.
I bought an AT clone and decided to use the nice new WD 1:1 interleave
MFM controller. Low level format succeeds, fdisk succeeds, format succeeds
with a few complaints about bad sectors. Next I loaded some software, 
with a few spurious track seeks, and then it happened. The boot sector
got trashed. No problem. Boot off the floppy, run 'sys c:' and reboot without
the floppy. Ahh, that's better.

Well after several rounds of this I thought the 1:1 interleave was just
too much for this drive. So I tried the whole re-format process with
several different interleaves and always the same results; trashed files
and boot sectors.

A month later I am intrigued by a WD 16 bit 1:1 RLL hard-disk-only controller.
Should I try it? What the heck. It's only $145. Well after changing the
HD address on the WD-MFM controller (making the RLL the primary controller)
I had a screaming 32MEG hard disk. I haven't had a single error yet, not one.

If you're still confused or not sure about MFM and RLL formmating then
just remember this: If you format a hard disk with RLL, the MFM you try
on it later will never be quite the same.

TVOE - The Voice Of Experience

-- 
__________________________________________________________________
                              |    Wayne S. Dinsmore
Make  it in Massachusetts,    |    AT&T Bell Labs   att!cbnews!wsd 
Spend it in New Hampshire.    |    Room MV-1X54     (508)960-6113