Path: utzoo!utgpu!water!watmath!clyde!ima!think!ortiz From: ortiz@think.COM (Luis F. Ortiz) Newsgroups: comp.arch Subject: Re: Connection Machine Message-ID: <13470@think.UUCP> Date: 11 Dec 87 14:55:44 GMT References: <3516@husc6.harvard.edu> Sender: usenet@think.UUCP Reply-To: ortiz@thyestes.think.com.UUCP (Luis F. Ortiz) Organization: Thinking Machines Corporation, Cambridge, MA Lines: 80 In article <3516@husc6.harvard.edu> reiter@harvard.UUCP (Ehud Reiter) writes: >The Connection Machine is usually presented as 64,000 1-bit SIMD processors >hooked up with a hypercube router. However, from talking to a few people who >have experience with it (the CM2, not the CM1), I get the impression that many >applications basically ignore the 1-bit processors and the hypercube router >(which is very slow - it takes 1 ms to send a message), and instead do all >their computing with the 2000 Weitek FPU's, and do all their communicating >with the "NEWS" system, which basically is a fast 2-D mesh interconnect. First, I would like to correct something. The CM-2 has no 2-D mesh interconnect between processors like the CM-1 does. It turns out that the hypercube connections between processors are suffcient to embed a N-D lattice in the M dimensional hypercube (where N < M). >That is, the alternative model of the Connection Machine which these >applications use is that it is a 2-D mesh of 2000 fast FPU's, backed by >512MB of memory and a very high bandwidth disk I/O system. Like a >modern-day version of the Illiac IV, I guess (but one that actually works, >unlike the Illiac). To me, anyways, this "Illiac" model seems much more >useful (for getting real work done) than the "hypercube" model. >My question is, how do people who are running real applications on the CM2 >use it? Does anyone who actually has a CM care to comment? I realize that >there is one serious application, the news-wire retrieval program, which does >use the 1-bit CPU's to do its communicating (although it doesn't use the >hypercube router very much) - are there other (commercial) applications >which use either the 1-bit CPU's or the hypercube router? > Just to mention a few of the projects that we have worked on: 1) FFT's: It turns out that you can directly use the hypercube communications structure of the CM to great advantage while still looking at the machine as a one dimensional sequence of processors. 2) 3-D Air flow: Here we map a 3-d lattice onto the hypercube and use each processor to simulate a vlume of air. 3) QED: Quantum electrodynamics can map nicely into a 4 torus with each processor keeping track of the field strength in eight directions. 4) Cellular Automata: This kind of a research application uses almost no (if any) floating point, and spends its time doing nothing but 1-bit operations interspersed with aribtrary dimensional lattice communications. I guess my real point is that the machine has a special features (like fast 1-bit arithmetic, fast floating point, and hypercube connectivity, that are used differently by different applications. The field of parallel processing is still young and, quite frankly, there is still a lot left to learn. When people try to use the machine, oftentimes they one idea as to how the problem is to be solved, but end up implementing it in a totally differnt manner. Often you are pleasantly surprised by something you though was difficult, turning out to be elegantly simple (like diffusion equation solutions). I think that viewing the CM-2 as being a 2-D mesh of floatinbg point processors is too limited. ---------------------------------------------------------------- Luis F. Ortiz Thinking Machines Corporation ARPANET: ortiz@think.com, ortiz@yale.edu UUCP: {decvax,harvard,seismo,cmcl2}!yale!ortiz, harvard!think!ortiz BITNET: ortiz@yalecs.BITNET "Whenever people agree with me, I always think I must be wrong." --- Oscar Wilde ----------------------------------------------------------------