Path: utzoo!attcan!uunet!cs.utexas.edu!csd4.csd.uwm.edu!mailrus!bbn!kurz-ai!simcha
From: simcha@kurz-ai.UUCP (Simcha Lerner)
Newsgroups: comp.binaries.ibm.pc.d
Subject: Re: High density disk drive & Low density diskette
Message-ID: <312@kurz-ai.UUCP>
Date: 24 Aug 89 17:19:40 GMT
References: <2734.24F37377@isishq.FIDONET.ORG>
Reply-To: simcha@kurz-ai.UUCP (Simcha Lerner)
Organization: Kurzweil A.I. Waltham, Mass.
Lines: 40


The problem with taking a 360KB diskette that has been written on a
1.2MB drive to a 360KB drive has to do with the different track
widths that the two drives' heads write. In essence, the 1.2 MB drive
leaves a border of unwritten media on either side of the track, which
the 360KB drive will end up reading.

My experience is that the best way to achieve reliable interchange is
to start with a never before used diskette, and only format and write
to it with one type of drive. This will give 98+% odds that the other
type of drive will be able to read it.

The ability of the 1.2MB drive to read a diskette written in a 360KB
drive is obvious, since it ends up reading the center of a track
wider than its head gap. The reason the 360KB drive can reliably read
a disk that was written on the 1.2MB is due to the border being
unformatted. Unformatted media has an average flux that cancels
itself out, allowing the flux of the narrow track that was written to
dominate.

If a diskette has been formatted or written by a 360KB drive, the
border will have flux values that contain data. Since the 1.2MB drive
leaves a border of this old data when it overwrites it, there is a
finite chance that this will cause read errors when returned to a
360KB drive with its wider head gap.

In any case, my personal practice is to NEVER write _critical_ data
on a 360KB disk in a 1.2MB drive if I am going to need to read it on
a 360KB drive. I get a 360KB drive installed instead.



-- 
Simcha Lerner
Kurzweil Applied Intelligence

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