From: jnc@mercury.lcs.mit.edu (Noel Chiappa)
To: tuhs@minnie.tuhs.org
Cc: jnc@mercury.lcs.mit.edu
Subject: Re: [TUHS] [tuhs] PDP-11 and early Unix
Date: Mon, 14 Mar 2022 16:22:53 -0400 (EDT) [thread overview]
Message-ID: <20220314202253.2CAFD18C083@mercury.lcs.mit.edu> (raw)
> From: Clem Cole
> I'm thrilled to see the 11 kept alive.
Ditto. The most elegant archtecture ever, IMO.
> I was under the impression ??Ken?? had created them for B
> independently (which, of course, was first on the PDP-7).
"The Development of the C Language", by Dennis M. Ritchie:
https://www.bell-labs.com/usr/dmr/www/chist.html
says:
The PDP-7, however, did have a few `auto-increment' memory cells, with the
property that an indirect memory reference through them incremented the cell.
This feature probably suggested such operators to Thompson; the
generalization to make them both prefix and postfix was his own. Indeed,
the auto-increment cells were not used directly in implementation of the
operators, and a stronger motivation for the innovation was probably his
observation that the translation of ++x was smaller than that of x=x+1.
Note the "probably"; unless Ken remembers, and says something, that's
probably the best we are going to get.
> I did not think the PDP-7 ISA includes addressing modes in the same
> manner as the 11. .. I thought PDP-7 is a very simple instruction (and
> small) with an AC, Link/Indirection and a PC - it reminded me of the
> PDP-8 more than anything else
The PDP-4, -7 and -9 are all the same architecture (very similar to the
PDP-1, but simplified a bit), differing only in implementation. (Most PDP-7
code will run on a -9, un-modified.) Basic instructions look like:
Instructions had a 4-bit opcode ('000'-'054'), 1 bit of indirect, and 13
bits of address. It was a load-store architecture, with a single accumulator.
So, yes, similar to an -8. There are other opcodes for non-memory operations
('074' opcode), and I/O ('070'), using bits in the 'address' field. ('060'
opcodes were for the optional EAE.) All of the -4/-7/-9 had the
'auto-increment on locations 010-017' when indirecting through them' feature.
Bitsavers has fairly complete docs on them all:
http://www.bitsavers.org/pdf/dec/pdp4/
http://www.bitsavers.org/pdf/dec/pdp7/
http://www.bitsavers.org/pdf/dec/pdp9/
Noel
next reply other threads:[~2022-03-14 20:25 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-14 20:22 Noel Chiappa [this message]
-- strict thread matches above, loose matches on Subject: below --
2022-03-14 20:38 Noel Chiappa
2022-03-14 16:56 Noel Chiappa
2022-03-14 18:00 ` Clem Cole
2022-03-14 19:03 ` Angelo Papenhoff
2022-03-14 12:58 Nelson H. F. Beebe
2022-03-14 14:59 ` Ron Natalie
2022-03-14 15:13 ` Clem Cole
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