Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10 5/3/83; site cornell.UUCP Path: utzoo!linus!wivax!decvax!harpo!floyd!vax135!cornell!hal From: hal@cornell.UUCP Newsgroups: net.arch Subject: Re: Cray vs ICs - (nf) Message-ID: <4687@cornell.UUCP> Date: Thu, 23-Jun-83 17:34:43 EDT Article-I.D.: cornell.4687 Posted: Thu Jun 23 17:34:43 1983 Date-Received: Sat, 25-Jun-83 22:04:35 EDT References: <2267@uiucdcs.UUCP> Organization: Cornell Computer Science Lines: 36 I recommend the article "The CRAY-1 Computer System" by Richard M. Russell of Cray Research (CACM vol. 21, no. 1, pp. 63-72, 1978), which explains, among other things, the reasons for the very simple chip types in the machine. (The four chip types are 16x4 bipolar register chips [6 ns. cycle], 1024x1 bipolar memory chips (50 ns), and two types of bipolar logic chips.) A paragraph near the end of the article is worth quoting: "CRAY-1 modules are 6 inches wide. The distance across the board is about a nanosecond which is just about the edge time of the electrical signals. Unless due precautions are taken, when electrical signals run around a board, standing waves can be induced in the ground plane. Part of the solution is to make all signal paths in the machine the same length. This is done by padding out paths with foil runs and integrated circuit packages. All told, between 10 and 20 per cent of the IC packages in the machine are there simply to pad out a signal line. The other part of the solution was to use only simple gates and make sure that both sides of every gate are always terminated. This means that there is no dynamic component presented to the power supply. This is the principal reason why simple gates are used in the CRAY-1. If a more complex integrated circuit package is used, it is impossible to terminate both sides of every gate. So all of the CRAY-1's circuits are prefectly balanced. Five layer boards have one ground layer, two voltage layers, and then the two logic layers on the outside. Twisted pairs which interconnect the modules are balanced and there are equal and opposite signals on both sides of the pairs. The final result is that there is just a purely resistive load to the power supply!" (Copyright (C) 1977, ACM, copied by permission) Folks who design supercomputers have strange and wonderous things to worry about. Hal Perkins uucp: {decvax|vax135|...}!cornell!hal Cornell Computer Science arpa: hal@cornell bitnet: hal@crnlcs