Extracting data from DEC VAX tape recordings

Dennis Boone drb at msu.edu
Sun Mar 19 14:01:19 CDT 2017

 > I have a rather crude way of reading 9-track tapes in 1600 and 6250
 > BPI densities.  I have worked out how to unpack VAX BACKUP format
 > tapes, if that is how they were written.  I have read some tapes that
 > were about this old, but they have been stored in excellent
 > conditions, and they were high-quality tapes.  Some tapes that were
 > of lesser quality or stored in poor conditions may not be
 > recoverable.

9-track tape is remarkably resilient.  I've successfully read tapes that
were stored in an uncontrolled Michigan attic for 20+ years.

VMS Backup format isn't that hard to deal with: there are at least one
or two open source tools which can read most save sets, and feeding an
image to an actual VMS system in emulation is easy too.

The worst threat is the "sticky shed" issue, wherein the binder which
holds the coatings onto the tape backing absorbs moisture and gets
gooey.  A number of approaches have been described in the literature,
from mechanically removing the back coating applied to some media to
reduce static and other issues, to chemical applications, to baking out
the moisture.

 > Some other people have a lot of experience with baking the tapes at
 > low temperature to improve the chances of good data recovery, you you
 > might see if they want to do it, first.

I've had good luck with the lowest of tech solutions: a food dehydrator.
Many libraries have used convection ovens.  Target temperature seems to
be in the neighborhood of 130-140 degrees.  I've seen recommendations
for 2-4 hours, but I seem to have better luck with 24.


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