Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!thunder.mcrcim.mcgill.edu!snorkelwacker.mit.edu!mintaka!olivea!samsung!sol.ctr.columbia.edu!emory!gatech!udel!nigel.ee.udel.edu!mccalpin From: mccalpin@perelandra.cms.udel.edu (John D. McCalpin) Newsgroups: comp.arch Subject: Re: IBM RS6000 Message-ID: Date: 10 Jan 91 22:26:01 GMT References: <1991Jan10.214122.9506@news.arc.nasa.gov> Sender: usenet@ee.udel.edu Organization: College of Marine Studies, U. Del. Lines: 54 Nntp-Posting-Host: perelandra.cms.udel.edu In-reply-to: lamaster@pioneer.arc.nasa.gov's message of 10 Jan 91 21:41:22 GMT >>>>> On 10 Jan 91 21:41:22 GMT, lamaster@pioneer.arc.nasa.gov (Hugh LaMaster) said: Hugh> Scientific researchers are beginning to get results on the IBM Hugh> RS6000 machines. [...] I heard two comments today, which Hugh> correspond with other things I have heard. Hugh> 1) The machines are as fast as other micros on scalar code, and Hugh> a lot faster on vector code (other things being equal: clock Hugh> speed, cache, etc. etc). Many of the codes here *are* Hugh> vectorizable. This is certainly consistent with the initial benchmarks, the Los Alamos report, and the general hearsay from around here. My RS/6000 runs vectorizable codes about twice as fast as a DECstation 5000 and scalar floating-point codes at about the same speed as a DECstation 5000. Unlike the MIPS-based machines, the RS/6000 often runs a bit *faster* in 64-bit precision than in 32 bits.... Hugh> 2) The machine is very, very bad at context switches. So bad, Hugh> that response time becomes terrible with *one* CPU bound Hugh> background process running. Hugh> Again, this is *hearsay*. But, I am particularly curious if Hugh> anyone has any insight on 2) above. Is it as bad as these Hugh> various sources have reported? This was also the result presented in "Personal Workstation". However, that magazine consistently exhibits an incredibly low level of understanding of computer performance issues, so it is difficult to give that particular result much credibility.... A contrary result was expressed in a recent issue of "Workstation News" (or some such title), which showed the RS/6000 as being much faster than the DECstation 5000 for multiple jobs. The DECstation 5000 was, in turn, much faster than the Sun 4?? (470 maybe?). As a side note on "scientific literacy", I threw the latter newspaper/magazine away when I noticed that the apparently *huge* differences in performance shown on the chart were simply an optical illusion produced by the choice of the range. The values were something like IBM 200 DEC 140 SUN 100 and the ordinate of the chart was from about 80 to 220, thus making the IBM line some 5 times as "high" as the SUN line (though the actual speed ratio was only 2:1) and making the DEC line about 3 times as "high" as the SUN line (with an actual ratio of 1.4:1). Perhaps "The Visual Display of Quantitative Information" should be require reading for journalists as well as scientists and engineers.... -- John D. McCalpin mccalpin@perelandra.cms.udel.edu Assistant Professor mccalpin@brahms.udel.edu College of Marine Studies, U. Del. J.MCCALPIN/OMNET