Path: utzoo!attcan!uunet!cs.utexas.edu!sun-barr!newstop!sun!amdcad!brahms!phil
From: phil@brahms.amd.com (Phil Ngai)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: Can you RLL format the Seagate ST251 drive?
Message-ID: <1990Sep16.070847.16262@amd.com>
Date: 16 Sep 90 07:08:47 GMT
References: <4285@trantor.harris-atd.com> <1990Sep10.162707.18613@amd.com> <11257@spool.cs.wisc.edu>
Sender: usenet@amd.com (NNTP Posting)
Distribution: na
Organization: Advanced Micro Devices, Inc; Sunnyvale, CA
Lines: 36

In article <11257@spool.cs.wisc.edu> peng@chaource.cs.wisc.edu (PENG) writes:
|I know Mitsubishi is advertising a drive (MR535?) that allows you to
|format as either an RLL or an MFM drive.  But I never see Seagate does this.
|So what's the catch?  Do RLL drives have to be better built?  And therefore
|Mitsubishi doesn't mind that their drives are being formatted in MFM? (because

It's not primarily a matter of how well they are built. The thing about
RLL is that, although it uses the same number of flux transitions as
MFM, they must be more precisely placed. Things like a poor signal
to noise ratio in the head amplifiers or imperfect write compensation
can cause a problem.  Apparently Seagate does not want to certify some
of their drives as RLL (although many of them do work that way).

I think all RLL drives can be used in MFM but there are plenty of
rumors about how you can't do this, so I believe the Mitsubishi
drive is really a RLL drive and Mitsubishi is simply trying to
reassure those people who do not have RLL controllers that they
can also use that disk.

In my limited experience, most reliable MFM drives work in the RLL
mode. I would expect that a drive which failed RLL to be pretty
marginal with MFM but I will not claim to be an expert at this,
I do feel I have an understanding of how MFM and RLL work at the
bit level.

No doubt someone will post about how he tried his MFM drive with
RLL and it caught fire and burned down his house, but I don't believe
it was because of the use of RLL.

And there are stories about how if you use an RLL drive with an
MFM controller it will give off X-rays and prevent you from having
any children, but you shouldn't believe them either.

--
Phil Ngai, phil@amd.com		{uunet,decwrl,ucbvax}!amdcad!phil
"Why would Xerox Corp. want a paperless office?"