From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: tuhs-bounces@minnie.tuhs.org X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=5.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_NONE autolearn=ham autolearn_force=no version=3.4.1 Received: from minnie.tuhs.org (minnie.tuhs.org [45.79.103.53]) by inbox.vuxu.org (OpenSMTPD) with ESMTP id d18d2a48 for ; Thu, 21 Jun 2018 16:13:26 +0000 (UTC) Received: by minnie.tuhs.org (Postfix, from userid 112) id 2CE349EE10; Fri, 22 Jun 2018 02:13:25 +1000 (AEST) Received: from minnie.tuhs.org (localhost [127.0.0.1]) by minnie.tuhs.org (Postfix) with ESMTP id 6D8FD9EC27; Fri, 22 Jun 2018 02:13:09 +1000 (AEST) Received: by minnie.tuhs.org (Postfix, from userid 112) id 642049EDE7; Fri, 22 Jun 2018 02:13:06 +1000 (AEST) Received: from mail1.g22.pair.com (mail1.g22.pair.com [66.39.65.155]) by minnie.tuhs.org (Postfix) with ESMTPS id 7184F9EDE5 for ; Fri, 22 Jun 2018 02:13:03 +1000 (AEST) Received: from mail1.g22.pair.com (localhost [127.0.0.1]) by mail1.g22.pair.com (Postfix) with ESMTP id 62C2A4840F4; Thu, 21 Jun 2018 12:13:02 -0400 (EDT) Received: from [172.16.0.147] (unknown [88.98.95.237]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail1.g22.pair.com (Postfix) with ESMTPSA id 109C94498F4; Thu, 21 Jun 2018 12:13:01 -0400 (EDT) Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 10.3 \(3273\)) From: Tim Bradshaw In-Reply-To: <201806211346.w5LDkJJG126945@tahoe.cs.Dartmouth.EDU> Date: Thu, 21 Jun 2018 17:13:00 +0100 Content-Transfer-Encoding: quoted-printable Message-Id: <9F50E0F4-25A5-40F9-90D7-B454BE0EF9D6@tfeb.org> References: <201806211346.w5LDkJJG126945@tahoe.cs.Dartmouth.EDU> To: Doug McIlroy X-Mailer: Apple Mail (2.3273) Subject: Re: [TUHS] core X-BeenThere: tuhs@minnie.tuhs.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: The Unix Heritage Society mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: tuhs@tuhs.org Errors-To: tuhs-bounces@minnie.tuhs.org Sender: "TUHS" On 21 Jun 2018, at 14:46, Doug McIlroy wrote: >=20 > Whether it was the (significant) mechanical part or the electronics > that typically broke is unclear. Failures in a machine that's always > doing the same thing are easier to detect quickly than failures in > a mchine that has a varied load. Also the task at hand could fail > for many other reasons (e.g. mistranscribed messages) so there was > no presumption of correctness of results--that was determined by > reading the decrypted messages. So I think it's a stretch to > argue that reliability was known to be a manageable issue. I think it's reasonably well-documented that Flowers understood things = about making valves (tubes) reliable that were not previously known: = Colossus was well over ten times larger than any previous valve-based = system at the time and there was huge scepticism about making it work, = to the extent that he funded the initial one substantially himself as BP = wouldn't. For instance he understood that you should never turn the = things off: even quite significant maintenance was done on Colossi with = them on (I believe they were kept on even when the room flooded on = occasion, which led to fairly exciting electrical conditions). He also = did things with heaters (the heater voltage was ramped up & down to = avoid thermal stresses when powering things on or off) and other tricks = such as soldering the valves into their bases to avoid connector = problems. The mechanical part (the tape reader) was in fact one significant reason = for Colossus: the previous thing, Heath Robinson, had used two tapes = which needed to be kept in sync (or, rather, needed to be allowed to = drift out of sync in a controlled way with respect to each other), and = this did not work well at all as the tapes would stretch & break. = Colossus generated one of the tapes (the one corresponding to the Lorenz = machine's settings) electronically and would then sync itself to the = tape with the message text on it. It's also not the case that the Colossi did only one thing: they were = not general-purpose machines but they were more general-purpose than = they needed to be and people found all sorts of ways of getting them to = compute properties they had not originally been intended to compute. I = remember talking to Donald Michie about this (he was one of the members = of the Newmanry which was the bit of BP where the Colossi were). There is a paper, by Flowers, in the Annals of the History of Computing = which discusses a lot of this. I am not sure if it's available online = (or where my copy is). Further, of course, you can just ask people who run one about = reliability: there's a reconstructed one at TNMOC which is well worth = seeing (there's a Heath Robinson as well), and the people there are very = willing to talk about reliability -- I learnt about the = heater-voltage-ramping thing by asking what the huge rheostat was for, = and later seeing it turned on in the morning -- one of the problems with = the reconstruction is that they are required to to turn it off at night = (this is the same problem that afflicts people who look after steam = locomotives. which in real life would almost never have been allowed to = get cold). As I said, I don't want to detract from Whirlwind in any way, but it is = the case that Tommy Flowers did sort out significant aspects of the = reliability of relatively large valve systems. --tim