Re: Disk imaging

[Rubywand <rubywand@swbell.net>]

Paul Grammens writes ...
> 
> Rubywand <rubywand@swbell.net> wrote
> >
> >  There are a number of factors which impact useful life of software on diskette. For instance, software on a 3.5" diskette is likely to have a much shorter life than a that on 5.25" diskette.
< <
> 
> That's interesting, I would have thought the other way
> around, just based on the better protection and more advanced
> technology of the 3.5" diskette.
> Any idea why the 3.5" diskettes are less reliable?
 ....

     Most likely, it has to do with less tolerance for error combined with
higher probability of error. For instance, a much smaller error in head
positioning can lead to overwriting bits in an adjacent track. 

     Experience with 5.25" diskettes (some going back to the early 1980's)
vs. 3.5" diskettes is that 3.5" diskettes are much less reliable. I've had to
trash quite a few 3.5" diskettes and only a few 5.25" diskettes; yet, we have
many more 5.25" disks.

     My guess is that the formulation used for DD 3.5" diskettes is not
consistently up to 800k density. (Maybe, a variety of formulations were
employed for DD.) One indication is that 3.5" HD diskettes are normally
formatted for just 1.4MB. This is a fairly small jump in density when you
consider the easily measured difference in the magnetic properties of DD vs
HD media.

     Putting this another way, we each probably have some 3.5" DD diskettes
which are doomed to screw up very soon and others which will be good for a
decade or more. Backing up 3.5" diskettes via ShrinkIt whole-disk archives is
a good idea.

     Another good practice is to backup and retire diskettes which exhibit
signs of 'weakness'-- like, file loads from the diskette are slow because the
drive is obviously having to reread blocks.

Note: By the way, avoid automatically trashing diskettes which are rejected
after booting from an IDE hard disk or SCSI drive. (Also, avoid ripping into
your 3.5" drive.)  Sometimes, the 3.5" drives are not correctly initialized
if no 3.5" diskette is present in Drive 1 when the IIgs is powered ON.
     


Rubywand