[inforoots] Recovering data from old media (Was: "The digital DarkAge")

[Keith Graham]

I've come across this thread a little late, but I've been buried in
writing a proposal - coincidentally - for the restoration and
preservation of a TV company's Video Archive (both Film and Tape).

The big problem with magnetic tapes (Oxide as opposed to Metal
Evaporated) is separation of the oxide from the backing material due to
aging of the binder. This is exacerbated by poor storage conditions, too
hot, too cold, widely varying temperatures, too dry, too humid - you
name it. Cleaning the tape, especially with fluid-based cleaners will
not help. In severe cases it will accelerate the separation of the
oxide. You wind up with a brown sludgy fluid and a see-through tape! 

What we do for the video boys is to bake the tape. There are specialist
companies that make ovens into which the tape is put and *gently* warmed
over a period of time. NOT 375 degrees for 1hr!! This has the effect of
stabilizing the oxide layer enough to allow 1 or 2 passes (at most) to
attempt to recover the data. We cannot expect the tape to return to it's
original state after this process, but it's often enough to recover the
material onto some other medium.

Film survives much better. A 60 year old film is often easier to treat
that a 15 year old tape.

Which begs the question as to whether the film chip data storage machine
in VS was not such a bad idea after all!

Keith Graham

-----Original Message-----
From: inforoots-bounces at computerhistory.org
[mailto:inforoots-bounces at computerhistory.org] On Behalf Of John C Green
Jr
Sent: Wednesday, September 28, 2005 3:11 PM
To: inforoots at computerhistory.org
Subject: [inforoots] Recovering data from old media (Was: "The digital
DarkAge")

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=======================================
At 07:35 PM 9/27/05, Mike Albaugh wrote:
>Texx wrote:
>
> > Our own musuem collection contains boxes of mag tape that we havent 
> been able
> > to read yet.  Alas Im sure some of it has succumed to bit rit.
>
>  Perhaps, depenidng on storage conditions, but the older stuff
>was 200 or 556 BPI, and as long as its on "decent" media,
>it may surprise you. Paul Pierce was able to recover all but
>a few blocks of a tape with the sources for a CDC 3600
>Timesharing O.S. from a 7-track tape for me, about two years
>back. And since then, he has revamped and improved his
>read electronics.

A couple or three decades ago Datamation had an article about
a Navy guy who found a room of old tapes that had never been
intended to be archived e.g. had not been slowly wound end to
end in both directions to relieve tension and minimize print
through, rather had been high speed rewound.

He tried to recover data from tapes that were over a decade
old.  There was a mix of 200, 556, and 800 BPI.  As there
were mostly 556 BPI he only did them.

Results ...
Trying to read directly: Total failure
Cleaning with do-it-yourself tape cleaners available at the
time: Mostly failure
Sending out to commercial cleaners: Excellent results.

He had a table of the bit error rates by tape manufacturer.
One manufacturer had two grades: Normal and Millennium with
the premium supposed to last far longer than the normal.
The Normal had a much better bit error rate than the
Millennium under the conditions of his room of tapes i.e.
no special care having been taken to make the tapes readable
a decade later.

The vendor of the Normal and Millennium tapes: IBM.

Regards,
JC Green


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