Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!watmath!clyde!cbatt!ihnp4!qantel!intelca!oliveb!hplabs!hp-sdd!ncr-sd!sdcsvax!sdcc6!loral!ian From: ian@loral.UUCP (Ian Kaplan) Newsgroups: net.arch Subject: Floating point performance Message-ID: <1242@loral.UUCP> Date: Thu, 25-Sep-86 16:52:50 EDT Article-I.D.: loral.1242 Posted: Thu Sep 25 16:52:50 1986 Date-Received: Tue, 30-Sep-86 06:47:12 EDT Organization: Loral Instrumentation, San Diego Lines: 78 Keywords: Floating Point, Microprocesors ABSTRACT The scalar performance of microprocessors is increasing much faster than the floating point performance of floating point coprocessors. Floating point performance is essential for many Fortran applications. The purpose of this note is to encourage microprocessor designers to concentrate more on floating point. The Current State of the World ------------------------------ The "big three" microprocessor manufacturers (iNTEL, Motorola and National Semiconductor) have all announced 32-bit microprocessors. These chips all have high scalar performance (at least for microprocessors). Unfortunately the speed of the floating point co-processors has not kept up. Below are some approximate speeds for the various math coprocessors. The performance listed is "peak" performance, which assumes that the operands are already in the floating point registers. Intel 80287 less than 0.1 MFLOP National 0.1 MFLOP Motorola 0.3 MFLOP Naturally these speeds will vary, depending on clock speed, but there are not far off. None of these coprocessors has performance that is close to 1 MFLOP. National has a chip (the 32310) that will allow the 32032 to be interfaced with the Weitek floating point ALU and multiply unit. This yields 0.8 MFLOPS with math error checking enabled and 1.2 MFLOPS with it disabled. Unfortunately the 32310 solution not only entails a significant increase in component price (a 32310, two Weitek chips and support logic), but also consumes a lot of board space and power. Whether the increase in floating point performance justifies these increased costs is arguable. I would like to get more MFLOPS for my bucks. We Need More MFLOPS ------------------- At one time (three years ago) 0.1 MFLOP was considered pretty good floating point performance. This is no longer true. Floating point performance tends to be measured now against the Weitek chips (or AMD or Analog Devices etc...) used in bit-slice applications (e.g., 10 MFLOPS). The floating point performance available with the Weitek chips would be wasted on the current generation of microprocessors. Even the fastest microprocessors currently available could not feed floating point operands to a coprocessor fast enough to keep up with the 10 MFLOP rate. What is needed is a coprocessor (or an integrated floating point processor) that will yield 1 to 2 MFLOPS. So far the only microprocessor that comes close to delivering 1 MFLOP of floating point performance is the Fairchild Clipper. The Clipper has an on chip floating point unit rated at about 1 MFLOP. Fortran, despite its many problems, is one of the most widely used programming languages. Despite the hopes of many computer scientists, Fortran will never disappear (there will just be new versions of Fortran). The increasing power of microprocessors means that more Fortran applications will be run on microprocessor based systems. Many Fortran applications are floating point bound, so the increased scalar performance provided by the current generation of 32-bit microprocessors will only speed them up fractionally. For these applications floating point performance will be the deciding factor. The microprocessor vendor that realizes the importance of floating point performance, and develops a solution, will capture a large number of designs where Fortran performance is important. Ian Kaplan Loral Dataflow Group Loral Instrumentation USENET: {ucbvax,decvax,ihnp4}!sdcsvax!loral!ian ARPA: sdcc6!loral!ian@UCSD USPS: 8401 Aero Dr. San Diego, CA 92123