I think the answer is two characters per 18b word, right aligned in a 9b
"byte".
This is based on the assembly code at the end of the first PDF:
a.out:
<a.>; <ou>; <t 040; 040040
Clearly it's just two characters per word (; denotes end of statement to
this assembler). 040040 is octal for space-space in ASCII, one character
per 9b in octal.
/Bob
On 2/25/2016 12:00 PM, [email protected] wrote:
Message: 1
Date: Thu, 25 Feb 2016 08:04:01 +1000
From: Warren Toomey<[email protected]>
To:[email protected]
Subject: [Simh] Questions about PDP-7
Message-ID:<[email protected]>
Content-Type: text/plain; charset=us-ascii
Hi all, recently we unearthed a set of pages that contain assembly listings
of the PDP-7 Unix kernel and some associated user-mode programs. See the files
0*.pdf athttp://www.tuhs.org/Archive/PDP-11/Distributions/research/McIlroy_v0/
There's a move afoot to see if we can bring this up on a real PDP-7 and also
on SimH. I've set up a mailing list if anybody wants to help out, and my
initial Github repository is athttps://github.com/DoctorWkt/pdp7-unix
I've got some PDP-7 questions and also some SimH PDP-7 questions. What is
the format of disk blocks that SimH stores for the 18-bit systems? In other
words, how are the 18-bit words in each block stored in the bytes of the
host systems? At some point we will need to write a tool to generate a
filesystem, so this information will be crucial.
A general PDP-7 question: how are ASCII strings stored in memory? Are
they 7-bit or 8-bit? I'm assuming that two ASCII characters are stored
in one 18-bit word, but which bits go where? If I had the string "abcd",
which bits go where in the two 18-bit words?
Thanks in advance for all your help, and also thanks to RMS and others
who wrote Simh as it's been an invaluable tool to keep the PDP-11 and
Vax Unix systems going.
Cheers, Warren
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