[Simh] Semi-OT: 7-bit binaries

[Johnny Billquist]

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: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol