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From: crs@cpsc6a.att.com (Chris (Beam me up, Scotty!) Seaman)
Newsgroups: comp.binaries.ibm.pc.d,comp.sys.ibm.pc
Subject: High/Low density disk/drive compatibility
Summary: There is one other problem...
Message-ID: <2329@cpsc6a.att.com>
Date: 25 Aug 89 22:48:55 GMT
References: <2734.24F37377@isishq.FIDONET.ORG> <312@kurz-ai.UUCP>
Organization: AT&T (CPSC), Oakland, CA
Lines: 51

simcha@kurz-ai.UUCP (Simcha Lerner) writes:
< 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.

This is the best way short of installing a 360KB drive in your machine,
at least.

< 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.

Actually, there is a potential problem when reading 360KB disks in a
1.2MB drive.  Suppose you have a 360KB disk, which formatted fine
on a 360KB drive, and you scribble some data onto it.  Now you
place the disk in a 1.2MB drive, and attempt a read.  However, the
surface of the disk looks like the following (any single track):

-----------------------------------------------------------
Area written by 360KB drive

- - - - - - - - - - - - - - - - /---------\ - - - - - - - -
Area read by 1.2MB drive       |  defect   |
- - - - - - - - - - - - - - - - \_________/ - - - - - - - -

Area written by 360KB drive
-----------------------------------------------------------

This is a crude representation, but I think you can get the idea.
The questionable track can be read by the 360KB drive, but will
consistently error on the 1.2MB.  You may say, "Sure, but how
often will this happen?".  Well, it happened to me within 2 weeks
of getting my 1.2MB drive.

< 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.

Ditto.  This was the only equitable solution I was able to come up
with, at least until I can copy all my files onto 1.44MB disks :-).

< -- 
< Simcha Lerner
< Kurzweil Applied Intelligence

-- 
Chris (Insert phrase here) Seaman |    ___-/^\-___
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