Path: utzoo!news-server.csri.toronto.edu!utgpu!watserv1!ria!uwovax.uwo.ca!baer From: baer@uwovax.uwo.ca Newsgroups: comp.sys.ibm.pc.hardware Subject: 387 math chip vs. 287 math chip Message-ID: <1991Mar8.175729.8757@uwovax.uwo.ca> Date: 8 Mar 91 22:57:29 GMT Lines: 41 Re: Intel 387 chips I understand that the 387 chip is supposed to be a big improvement over the 287 chip. I have heard manufacturers claim that it works up to 5x as fast (though some of this difference will evidently be attributable to clock speed differences). I believe this claim is overblown. I tried running a math-intensive application on 2 machines I own. One is a 286 w/ 287 , and the other is a 386sx w/387sx. (I also ran the application on a 386dx-20/no cache with a 387 chip). The application is *quite* math intensive: although it runs without the co-processor, in earlier tests with other machines, I ascertained that it speeds up by a factor of between 5 and 10 with the math chip (vs. no chip on an equivalent machine). The application involves stats work probably originally written in Fortran -- with a lot of matrix inversions/multiplications, etc. Probably little or no trig. Here are the timings: 286 10mHz. w/ 287 - math chip is rated at 8mHz.; not sure if the clock speed of the chip is 8mHz. or 10*(2/3) = 6.67 mHz. 1273 seconds 386sx 16mHz w/ 387sx - 623 seconds 386dx 20mHz no cache w/ 387 456 seconds Now, most of the differences above can be attributed to speed differences in the clock speed at which the chips were running: the 286 takes twice as long, but we'd expect that from a chip that's running at half the speed. I expected a bigger speed difference between the sx and the dx given the fact that the application does gobble a bit of memory -- after all, 456/623 = .73 -- approximately the speed ratio between 20 mHz. and 16 mHz. (though, in fairness, the absence of a cache for the dx could have slowed it down). I'm not saying that the 387 chip mightn't be faster for certain applications (correcting for clock speed) -- I've read that its improvements for trig functions are important, and this could be important for CAD applications (though the overall speedup in many CAD applications with a math chip -- vs. without -- is nowhere near the overall speedup with math intensive applications grinding away with matrix inversion routines). -- --------------------------------------------------------------------- Douglas Baer, University of Western Ontario, London, Canada N6A 5C2 Internet: BAER@UWO.CA Bitnet: BAER@UWOVAX