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From: mikey@bbimg
Newsgroups: net.micro.pc
Subject: Re: Orphaned Response
Message-ID: <-217500@bbimg>
Date: Thu, 17-Apr-86 12:32:00 EST
Article-I.D.: bbimg.-217500
Posted: Thu Apr 17 12:32:00 1986
Date-Received: Mon, 21-Apr-86 04:47:02 EST
References: <1484@mtuxo.UUCP>
Lines: 35
Nf-ID: #R:mtuxo.UUCP:1484:bbimg:-217500:000:1697
Nf-From: bbimg!mikey    Apr 17 11:32:00 1986


> When 360K floppies are written by a 1.2M drive, however,
> they are not always perfectly readable on a 360K drive.
> It helps if the floppy was formatted on a 360K drive.

WRONG!!!!!!!!

The problem is the narrow head width of the 1.2 meg floppy drive
lowering S/N when read on a 360K drive.  DO NOT format on a 360K
drive and then write on a 1.2M unit, this is the quickest way to
insure that the diskette will have problems when returning to a 360K
unit.  To make the diskettes readable on a 360K unit, BULK ERASE them
FIRST, then FORMAT (40tk mode) and WRITE to them on the 1.2M unit.  THEN
use the 360K unit to --->>> READ THEM ONLY!!!!<<<---.  When a 360K
unit writes, it puts down a wider track than the 1.2M unit.  Since
the 1.2M unit leaves some of this when it writes (it double steps) 
when the 360K units try to read, it reads a NARROW data channel with
a NARROW trim erase band, with the OLD DATA causing noise around the
track!  This is also the problem with the 80 track drives as used
in the Tandy 2000.

There is the possibility that if both drives are in perfect alignment,
formatting on the 360K will lay down a guard band that the 1.2M will
EXACTLY center in when it writes, but this is the real world, I don't
believe in tooth fairies or units that might be 'perfect' just 
because they work once.  
 
Understand how floppys work, they lay down a wide band of data, then a trim
erase (DC) comes along and clips the sides of the data band so that there is
a data track with a 'silent' buffer on either side.  The head reads 
wider than just the data track and the 'guard bands' are needed to be
'silent' for higher S/N ratio.

				Mike Yetsko 
				trsvax!techsup!bbimg!mikey