Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site cmcl2.UUCP Path: utzoo!watmath!clyde!burl!ulysses!allegra!bellcore!decvax!genrad!panda!talcott!harvard!seismo!cmcl2!gottlieb From: gottlieb@cmcl2.UUCP (Allan Gottlieb) Newsgroups: net.arch Subject: Re: Cube designs Message-ID: <814@cmcl2.UUCP> Date: Fri, 1-Mar-85 20:05:53 EST Article-I.D.: cmcl2.814 Posted: Fri Mar 1 20:05:53 1985 Date-Received: Mon, 4-Mar-85 07:46:28 EST References: <7306@watrose.UUCP> <798@loral.UUCP> Reply-To: gottlieb@cmcl2.UUCP (Allan Gottlieb) Organization: New York University Lines: 34 Summary: Although I would agree that programming parallel processors is inherently more difficult that programming serial machines, the additional effort required need not be as great as some contributers have indicated. There is a significant architectural variation in parllel machines and some are easier to program than others. We believe that with Shared Memory MIMD machines, applications programs do not resemble operating systems. For example we have modified the NASA "weather code" (the GISS atmospheric simulation program). This is a several thousand line FORTRAN program that doubtless represents multiple manyears of development. Our conversion required considerably under 1 man year. We have done many other largish scientific codes and have never required nearly as much time to parallelize the code as the original development. Thus for those problems, producing parallel programs is bounded by twice the serial effort. There is a price to pay for this relative programming ease. Our design (the NYU Ultracomputer) includes a sophisticated (and expensive) processor to memory interconnection network that, among other things, can satisfy multiple simultaneous memory references to the same word in just the time required for one such reference. Since this network will have a non-negligible component count, the same amount of money will buy more computing power if used for a cube, or other nonshared memory design. On the subject of operating systems our currently operational "symmunix" is largly parallel (concurrently executed by multiple processors) and symmetric (no master-slave relationships). Ask its principle author (cmcl2!edler) for details. -- Allan Gottlieb GOTTLIEB@NYU {floyd,ihnp4}!cmcl2!gottlieb <---the character before the 2 is an el