Re: The Saltine's Disks Archived at Mac GUI Vault

["Michael J. Mahon" <mjmahon@aol.com>]

Moose wrote:
> > I agree that it's a great donation, but it's not at all surprising
> > that all the disks still work.
> >
> > Unless a disk was of very low quality at the start, or was subjected
> > to very punishing conditions since, 5.25" floppies should continue
> > to work after all these years.
>
>
> You've got a lot more experience that me with this Michael.
>
> Around 1999/2000, I tried to backup about 20 of my old Apple ][ disks,
> and IIRC, only about 2/3 were still OK, and they had been stored in
> "gentle" conditions, had not been punished, and most were reasonable
> quality disks (Data Life, etc).  Here we are 10 years later, and I'd
> pleasantly surprised if half still worked.  (Sadly, my Apple ][c is
> dead so I currently have no way of checking).
>
> I have just gone through and checked all of The Saltine's disks, and
> of the 160 disk images, 108 seemed fine, 50 had errors, and 2 I wasn't
> sure about.  e.g. data disks for games that could well have "strange"
> formats.
>
> If anyone would like to read my brief report, I have uploaded it here:
>
> The_Saltines_Disks__Disk_Check_Results__v1.0__Moose__21-Mar-2011.pdf
> (16KB)
> http://www.mediafire.com/?rm0976h97jldw8w

(I couldn't find this file when I checked.)

It would be very interesting to see some of the disks that had errors.

In my experience, if there is no mechanical damage (scratches, creases,
flaking oxide, etc.), then mold spots can make a disk unreadable until
they are carefully cleaned off.

Aside from disks, by far the biggest cause of disk errors is a dirty
or slightly misaligned drive head, or an off-speed drive.  It's about
50-50 whether the "bad" drive was the one used to write the disk or
the one used to read it.  In the case of speed or alignment issues,
if the same drive is used to write and read, no or few errors will
occur.

It is possible to have an "adaptive" drive (never used for writing)
whose speed and alignment are adjusted to get the best read of a
disk or group of disks.  Though this can be a bit labor intensive,
if the data is important, it can be quite helpful.

While we usually focus on the age of the disks as a problem, an even
bigger problem can be the age of the drive--specifically the age of
the rubber drive belt.  As these age, they harden, taking on the "set"
of the position in which they have been resting.  The result is that
the rotational speed of the drive "wows" badly once per belt rotation.
These fluctuations can be far beyond what the state machine can
tolerate.

A simple fix for belt problems is using a half-height drive, which
usually has a direct hub drive, eliminating the rubber belt completely.

When I spoke of storing disks in a benign environment, that includes
keeping them free of high humidity and condensation, as well as free
from compression, magnetic fields (particularly AC magnetic fields),
and, of course, in a human-friendly temperature range.

-michael

NadaNet 3.1 for Apple II parallel computing!
Home page:  http://home.comcast.net/~mjmahon/

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