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

[Charles H Sauer]

On 11/27/2021 9:25 AM, Noel Chiappa wrote:
>      > 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
> contents.)

The notion of "baking" is slightly misleading. When done with audio 
tapes, the practice is to use a dehydrating oven at about 130F for about 
24 hours.

> 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.
> 
>        Noel
> 

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