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From: fisher@sc2a.unige.ch (Markus Fischer)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Question about diskette densities
Message-ID: <97@sc2a.unige.ch>
Date: 25 Jun 89 22:53:18 GMT
References: <2210@bingvaxu.cc.binghamton.edu>
Organization: University of Geneva, Switzerland
Lines: 39

In article <2210@bingvaxu.cc.binghamton.edu>, vu0112@bingvaxu.cc.binghamton.edu (Cliff Joslyn) writes:
> I'm beginning to doubt common sense about diskette densities.  Both
> single and double sided diskettes can be formatted as if they were
> double.  I'm told it's simply a difference in quality control.  On my
> new 1.2 meg 5.25" drive I can format DS/DD disks at 1.2 meg?  What am I
> risking by not buying HD disks?  etc.

Well, i expored the same topic with the first AT i had access to.  The most
visual approach is to use Norton's Utilities, whith the `map disk usage'
command.  As it appeares, the magnetic response of DSDD diskettes is high
enough for the EXTERNAL CYLINDERS to be formatted as DSHD.  But, as the
rotation speed of the drive is constant (i actually heard say of a variable
speed drive, i.e. more sectors on the outside... !), the density gets below
tolerance in the inside cylinders, thus failing format's own tests and
being marked as bad.  When you look at the results with a `disk-map' utility,
you will see that the limit between `good' and `bad' is a statistical one.
Personally, i wouldn't trust the lone good cluster in the middle of bad ones!

You must be warned about something else:  The heads of a 1.2 Mb drive are
smaller than those of a 360 kb.  This means that when you modify information
stored on a DD (360) diskette using a 1.2 Mb drive, you don't update the
entire track !  This means that you might be unable to read the modified
diskette on  your old 360-drive.  The only solution is then to format an
unused DD diskette whith the /4 option and to use `diskcopy' or `xcopy'.
(Then there is only the small track, no old parasites)

So my answer to your original question is: if you follow the manuals, you
won't risk (more than usually) to loose data.  And if you use the right kind
of diskette for your drives (i.e. no DD diskettes in 1.2 Mb drives, even with
the /4 option), you won't loose time (i.e. arriving to a site with unreadable
data...)

Markus Fischer                -|--|--|--|--|--|--I   Department of Anthropology
                        -|--|--|--|--|--|--|-(#)-I   University of Geneva
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black (#) to kill ! --|--|-(#)(_)(_)(_)(#)(#)(_)(_)  fisher@sc2a.unige.ch
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