[TUHS] PL/I stuff - was: Book Recommendation

Noel Chiappa jnc at mercury.lcs.mit.edu
Sun Nov 28 01:25:27 AEST 2021

    > From: "Charles H. Sauer"k <sauer at technologists.com>

    > I haven't done anything with 9 ktrack tapes for a long time ...
    > I don't recall problems reading any of them. ...
    > IMNSHO, it all depends on the brand/formulation of the tape. I've been 
    > going through old audio tapes and digitizing them 

The vintage computer community has considerable experience with old tapes; in
fact Chuck Guzis has a business reading them (which often includes converting
old file formats to something modern software can grok).

We originally depended heavily on the work of the vintage audio community, who
pioneered working with old tapes, including the discovert of 'baking' them to
improve their mechanical playability. ("the binder used to adhere the magnetic
material to the backing ... becomes unstable" - playing such a tape will
transfer much of the magnetic material to the head, destroying the tape's

It's amazing how bad a tape can be, and still be readable. I had a couple of
dump tapes of the CSR PWB1 machine at MIT, which I had thoughtlessly stored in
my (at one period damp) basement, and they were covered in mold - and not just
on the edges! Chuck had to build a special fixture to clean off the mold, but
we read most of the first tape. (I had thoughtfully ade a second copy, which
read perfectly.)

Then I had to work out what the format was - it turned out that even though
the machine had a V6 filesystem, my tape was a 'dd' of a BSD4.1c filesystem
(for reasons I eventually worked out, but won't bore you all with). Dave
Bridgham managed to mount that under Linux, and transform it into a TAR
file. That was the source of many old treasures, including the V6 NCP UNIX.


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