Path: utzoo!mnetor!uunet!mfci!root From: root@mfci.UUCP (SuperUser) Newsgroups: comp.arch Subject: Vector machines (was Re: FORTRAN Horror) Message-ID: <318@m3.mfci.UUCP> Date: 30 Mar 88 15:15:49 GMT References: <1135@pembina.UUCP> <46500011@uxe.cso.uiuc.edu> <6630@ames.arpa> Reply-To: mfci!colwell@uunet.UUCP (Robert Colwell) Organization: Multiflow Computer Inc., Branford Ct. 06405 Lines: 40 In article <6630@ames.arpa> lamaster@ames.arc.nasa.gov.UUCP (Hugh LaMaster) writes: ....[Fortran vs. C stuff deleted].... > >Again, the payoff on a vector machine can be much more than a factor of >two. True, it doesn't matter how fast most code runs. But it does >matter how fast certain very important (to you, the user) codes run. >And now that vector machines are reaching the market of below $100 K >machines, you will have an opportunity to see which codes will run >much faster. You may be pleasantly surprised. Or then again, if what you bought was a vector machine, you may come to agree with Olaf Lubeck of Los Alamos. In his recent "Supercomputer Performance: The Theory, Practice, and Results" tech report, LA-11204-MS, he concludes with the following: "Today both laboratories [Los Alamos and LLLabs] are running vector processors at 70 percent average vectorization levels. Because of Amdahl's law, the overall performance difference (at this vectorization level) between a low-speed vector unit and one an order of magnitude faster is negligible. We must have vectorization levels at the 95% level to see a significant difference and after ten years of fector experience, this level has simply not been attained....The fact is that it is difficult to organize computations so that *exactly* the same instruction operates on multiple elements of a data set..." "Faced with this sobering assessment of where we stand after 10 years of vectorization, I begin to wonder whether vectorization has a substantial place in future supercomputer architectures. The major reason that these architectures prosper today is that they have a significant scalar speed advantage over contemporary mainframes. I believe that future supercomputers are not necessarily bound to vector processing...." You don't need a vector machine to speed up vectorizable code. Bob Colwell mfci!colwell@uunet.uucp Multiflow Computer 175 N. Main St. Branford, CT 06405 203-488-6090