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From: clyde@hitech.ht.oz (Clyde Smith-Stubbs)
Newsgroups: comp.sys.ibm.pc
Subject: Re: MFM as an RLL drive?
Message-ID: <423@hitech.ht.oz>
Date: 21 Dec 89 23:55:31 GMT
References: <887@crash.cts.com> <28373@amdcad.AMD.COM> <44809@bu-cs.BU.EDU>
Organization: HI-TECH Software, Brisbane, QLD, Australia
Lines: 31

ngeow@bu-cs.BU.EDU (Yee Ngeow) writes:

>  Please note that running an MFM drive as RLL DEFINITELY CAN HURT
>it physically. Running an MFM at RLL push the drive electronics at
>50% higher clock rate then an MFM. As with any electronic components, this

Would someone who knows what they are talking about please stand up
and clear this up: to my knowledge the difference between MFM and RLL is NOT
that the clock rate is different, but that RLL has less redundant information,
i.e. to record one MFM bit takes two transitions while to record one
RLL bit takes only 1 point something transitions. If this is the case, then
the drive electronics surely are unaware of the difference? The only thing
that should matter is the stability of the drive (i.e. motor flutter etc.)
because of the reduced redundancy.

One thing that would affect an old drive being used with a new controller
is the difference in step rate. Older drives (e.g. the old Shugart 10MB
drives) could not accomodate buffered seek so maybe putting one of these
on a new controller that is toggling the step line at a high rate could
cause damage to the drive. Virtually all ST506 (really ST412) drives made
in the last few years should not be affected by this.

Incidentally I have formatted a Micropolis 1335 (MFM) as RLL and it came
up ERROR-FREE! When formatted as MFM it has bad sectors. I still entered
the factory bad tracks manually to be safe.

-- 
Clyde Smith-Stubbs
HI-TECH Software, P.O. Box 103, ALDERLEY, QLD, 4051, AUSTRALIA.
ACSnet:		clyde@hitech.ht.oz		PHONE:	+61 7 300 5011
UUCP:		...!nwnexus!hitech!clyde	FAX:	+61 7 300 5246