Odd "endianness" [was Re: RE: Base 64 posts to the list]
RichA at livingcomputers.org
Wed Dec 14 13:11:24 CST 2016
From: Lars Brinkhoff
Sent: Wednesday, December 14, 2016 3:54 AM
> Noel Chiappa wrote:
>>> 9-track tapes on the PDP-10 used one of the following encodings:
>> What about 7-track, any idea? I would assume 6 x 6-bit tape frames per
>> 36-bit word, but that's just a guess.
> A reasonable guess, and one I'd make too. But I don't know either.
According to the monitor calls manuals for both Tops-10 and TOPS-20, as
well as the manual specifically on tape labels etc., that's a very good
guess, and a correct one.
> Supposedly, many ITS backups were made to 7-track tapes. That became a
> problem when the old tape drives started to fail, and available new tape
> drives were only 9-track.
The same issue occurred at SAIL for the early WAITS backups prior to the
introduction of a KL-10 into the system (which grew from a PDP-6 to a
PDP-10/PDP-6 to a KL-10/KA-10/166, then shrank to a KL-10/KA-10 down to
a KL-10 only). The KL-10 had TU-78 drives on an RH20.
AIUI, the older backup tapes were refrangled onto new 9-track media before
the KA-10 and its drives were retired.
Vintage Computing Sr. Systems Engineer
Living Computer Museum
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Seattle, WA 98134
mailto:RichA at LivingComputerMuseum.org
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