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From: legg@sirius.ua.oz.au (Christian Legg)
Newsgroups: comp.sys.mac.hardware
Subject: Re:HD disks in a low density drive
Message-ID: <646@sirius.ua.oz.au>
Date: 28 Nov 89 22:22:39 GMT
Reply-To: legg@sirius.ua.oz.au (Christian Legg)
Organization: Computing Services, Uni of Adelaide, Australia
Lines: 29

Vaughan Turner (vturner@nmsu.edu) writes...

>I heard somewhere that High Density Mac Disks shouldn't be used on a
>low density drive (400 or 800K).  I kindof understand why this might
>be, but I was wondering if anyone could point me towards some
>technical information that confirms this (or not, I'd just like to
>know which it is).

Well Vaughan, I believe the answer that you are looking for is a technical one.
It is possible to format an HD disk in a Plus or SE (or similar 800k drive
equipped Mac) and use it as a 400/800 k disc. However, if you then place
this disk into a Mac with an HD disk drive it will try to read the disk as a
1.44 meg disk regardless. This is enforced by hardware - the Mac detects the
extra hole in the disk and assumes that it is a 1.44 meg disk. Thus, it
considers the 800k disk as faulty and gives you the option of formatting it.

This problem could probably be overcome by blocking the high density hole, but
then you may as well use normal 800k capable disks!

    Christian Legg

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* Christian Legg,                *                                          *
* University Computing Services, *  'Base 8 is just like base 10 really...  *
* University of Adelaide.        *  ...if you're missing two fingers.'      *
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* (08) 228 5549                  *                       Tom Lehrer         *
* ACSnet : legg@sirius.ua.oz     *                                          *
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