From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=5.0 tests=MAILING_LIST_MULTI, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.4 Received: (qmail 13281 invoked from network); 14 Mar 2022 20:25:37 -0000 Received: from minnie.tuhs.org (45.79.103.53) by inbox.vuxu.org with ESMTPUTF8; 14 Mar 2022 20:25:37 -0000 Received: by minnie.tuhs.org (Postfix, from userid 112) id 8CA909D660; Tue, 15 Mar 2022 06:25:36 +1000 (AEST) Received: from minnie.tuhs.org (localhost [127.0.0.1]) by minnie.tuhs.org (Postfix) with ESMTP id C81D59D605; Tue, 15 Mar 2022 06:22:57 +1000 (AEST) Received: by minnie.tuhs.org (Postfix, from userid 112) id 791EE9D605; Tue, 15 Mar 2022 06:22:55 +1000 (AEST) Received: from mercury.lcs.mit.edu (mercury.lcs.mit.edu [18.26.0.122]) by minnie.tuhs.org (Postfix) with ESMTPS id 244479D5FB for ; Tue, 15 Mar 2022 06:22:54 +1000 (AEST) Received: by mercury.lcs.mit.edu (Postfix, from userid 11178) id 2CAFD18C083; Mon, 14 Mar 2022 16:22:53 -0400 (EDT) To: tuhs@minnie.tuhs.org Message-Id: <20220314202253.2CAFD18C083@mercury.lcs.mit.edu> Date: Mon, 14 Mar 2022 16:22:53 -0400 (EDT) From: jnc@mercury.lcs.mit.edu (Noel Chiappa) Subject: Re: [TUHS] [tuhs] PDP-11 and early Unix X-BeenThere: tuhs@minnie.tuhs.org X-Mailman-Version: 2.1.26 Precedence: list List-Id: The Unix Heritage Society mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: jnc@mercury.lcs.mit.edu Errors-To: tuhs-bounces@minnie.tuhs.org Sender: "TUHS" > 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