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From: nigelm@ohm.york.ac.uk (Nigel Metheringham)
Newsgroups: comp.sys.ibm.pc.hardware,comp.multimedia,comp.misc,connect.audit
Subject: Re: Diffs between DD & HD disks
Message-ID: <1991Apr18.080421.1217@ohm.york.ac.uk>
Date: 18 Apr 91 08:04:21 GMT
References: <1991Apr17.000314.29195@ibmpcug.co.uk>
Organization: Electronics Department, University of York, UK
Lines: 34

In <1991Apr17.000314.29195@ibmpcug.co.uk> hdrw@ibmpcug.co.uk (Howard Winter) writes:

>No - you CANNOT reliably use DD disks as HD - especially 5.25".
>You can certainly format them (there is no physical indication
>of the disk type, as there is with 3.5") but you will find that
>the Format program reports about 25% bad sectors.  The inner tracks
>just cannot take the density unless they are made of the correct
>material - and 360K disks just aren't.

This applies just as much to 3.5 inch disks.  We have just had a set
of people demonstrating software at an exhibition here.  One bloke
had bought his precious programs with him (only one copy) on some
3.5 inch 720KB disks with the extra hole punched in them to persuade
the PC that they were really 1.4MB disks (apparently his Lab had run
out of disks in the few days before he came to the exhibition).

Our systems could read about 75% of the disk, but wouldn't touch the
inner tracks on any of the drives we tried.

The morals (probably loose) of the story are:-
    1.  Use disks of the correct type for the capacity you want.
    2.  Always have a second copy.
    3.  If its important have an extra set of copies, or some
        other way of rebulding it.
    4.  If its very important don't let it near a computer in 
        the first place :-) !


        Nigel.
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