On 2017-02-01 15:50, Timothe Litt wrote:
On 01-Feb-17 08:54, Lars Brinkhoff wrote:
Rich Alderson wrote:
On 9-track tape, in the default mode for all PDP-10 operating systems,
referred to as core-dump mode, 36 bit words are stored into 5 8-bit
frames (with logical parity) as follows:
bits 0-7 x x x x x x x x P
bits 8-15 x x x x x x x x P
bits 16-23 x x x x x x x x P
bits 24-31 x x x x x x x x P
bits 32-35 0 0 0 0 x x x x P
I thought so too. But I had a reason to look into chapter 3 of the TM10
maintenance manual, and I saw something interesting.
Apparently, the TM10 does a slight variation (or is this the canonical
version?) of the core dump format. It writes the last *six* bits to the
last frame, so bits 30 and 31 are actually written to two places:
Different controllers did different things; the TM10 replicates/ors the
bits. The Massbus tapes (TU45/77/78/79 on TM02/TM03) and the STC (TU7x
on DX10/DX20) wrote zeros.
Nitpicking - the TU78 do not use the TM02/TM03. It uses something called
the TM78. I never saw a TU79, but I can imagine it might have existed,
since there definitely was a TA79.
The TM78 have lots more registers than the TM02/TM03. I think it was
also dual-port by default, without any additional hardware, which was
required with the TM02/TM03.
And yes, tapes are definitely fun. I was working on getting the TU78
working under RSX for a while, but put the project away at one point,
and then our TU78 stopped working.
Johnny
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: [email protected] || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
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