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 26643 invoked from network); 1 Mar 2022 00:48:14 -0000 Received: from minnie.tuhs.org (45.79.103.53) by inbox.vuxu.org with ESMTPUTF8; 1 Mar 2022 00:48:14 -0000 Received: by minnie.tuhs.org (Postfix, from userid 112) id E0AA89CE72; Tue, 1 Mar 2022 10:48:12 +1000 (AEST) Received: from minnie.tuhs.org (localhost [127.0.0.1]) by minnie.tuhs.org (Postfix) with ESMTP id 31AD89CC02; Tue, 1 Mar 2022 10:46:40 +1000 (AEST) Received: by minnie.tuhs.org (Postfix, from userid 112) id A46E59CC02; Tue, 1 Mar 2022 10:44:24 +1000 (AEST) Received: from mercury.lcs.mit.edu (mercury.lcs.mit.edu [18.26.0.122]) by minnie.tuhs.org (Postfix) with ESMTPS id 1F9729CBCE for ; Tue, 1 Mar 2022 10:44:24 +1000 (AEST) Received: by mercury.lcs.mit.edu (Postfix, from userid 11178) id EB7A118C07B; Mon, 28 Feb 2022 19:44:22 -0500 (EST) To: tuhs@minnie.tuhs.org Message-Id: <20220301004422.EB7A118C07B@mercury.lcs.mit.edu> Date: Mon, 28 Feb 2022 19:44:22 -0500 (EST) From: jnc@mercury.lcs.mit.edu (Noel Chiappa) Subject: Re: [TUHS] Memory on Lion's v6 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: Will Senn > Does anybody know how much memory was configured on the PDP-11 that > Lion's used for the commentary system. Here's what the book says about > the system: > .. > ; PDP11/40 processor; > ... > It seems like he must have had an MMU V6 absolutely requires an MMU; the need for it is all throughout basic attributes of the system - e.g. user processes start their address space at 0. (BTW, there are V6 descendants, MINI-UNIX: http://gunkies.org/wiki/MINI-UNIX and LSX, which don't use/need an MMU, and run on -11 models without memory managament, such as -11/05's, but I don't think they were in wide use outside Bell.) > and 128k memory The -11/40, as originally released, only supported the MM11-L, which came in multiples of 16KB (for a 3-board set). Use of the later MM11-U (32KB units) required a new main power harness, which only came in on higher-serial-numbered -11/40's. The -11/40 (as it was at first) that I had at LCS had, to start with, I'm pretty sure, 3 MM11-L units (i.e. one MM11-L backplane full) - i.e. 48KB. I know this sounds incredible, and I'm having a hard time believing it myself, wondering if my memory is failing with age; but it definitely had extraordinarily little. I just looked on my V6 (running in a simulator), and it appears that by trimming all parameters (e.g. number of disk buffers) to the absolute bone, the kernel could be trimmed to about 36KB. (I haven't actually tried it, since I don't feel like recompiling all the kernel modules, but one can estimate it - take the current system size [44KB], delete 10 buffers @ .5KB gives 39KB, etc, etc.) That would allow a maximum user process of 12KB on a 48KB machine - and MINI-UNIX, which runs basically stock V6 user code, can manage with user processes that small. I see Andrew's email which reports that the Lions machine had more main memory, 128KB (maybe 4 MM11-U's - two MM11-U backplanes full); that woould have made their life a lot easier. Noel