Path: utzoo!attcan!utgpu!news-server.csri.toronto.edu!rutgers!cs.utexas.edu!wuarchive!julius.cs.uiuc.edu!rpi!uupsi!rodan.acs.syr.edu!amichiel From: amichiel@rodan.acs.syr.edu (Allen J Michielsen) Newsgroups: comp.sys.ibm.pc.hardware Subject: Re: Cyrix CX-803D87-20 Coprocessor Message-ID: <1990Sep30.160127.3442@rodan.acs.syr.edu> Date: 30 Sep 90 16:01:27 GMT References: <128@thor.UUCP> <1990Sep27.060417.23408@agate.berkeley.edu> <1969@sixhub.UUCP> Followup-To: amichiel@sunrise.acs.syr.edu Organization: Syracuse University, Syracuse, NY Lines: 47 >In article <1990Sep27.060417.23408@agate.berkeley.edu> ilan343@violet.berkeley.edu writes: >| I have seen adds for Cyrix FastMath coprocessor (80387 compatible) that >| claims 3X speedups. Are there any benchmarks to support this? >| Also, is compatibility an issue? At risk of starting a flame fest (pump, pump, pump, light).... When cyrix (or anyone) claims a 3X or whatever speedup with stuff og this type they REALLY are saying (in this case) that the average (or some measure) 80x87 instruction is performed in 1/3 the number of clock cycles. To you as a user, you will see virtually NO difference (generally) once the entire system is assembled. A typical application such as lotus or autocad does use the 80x87, but a. the instruction mix they use almost certainly doesn't line up with the one the claim was made using, & b. the stream of 80x87 instructions is intermixed. For 1 80x87 instruction, there may be 50 or 100 80x86(8) & memory:I/O related instructions. Using this model, with the original claim, and some wild ass extrapolations, it should be clear that while the 80x87 is important, just popping one in (or changing it) won't ever lead to ANYTHING even remotely approaching nX speed ups. As a matter of fact, with lotus and any speadsheet I have (distributed or my own), the difference with or without a 80x87 is som small I can't even measure it. On the other hand, in autocad, the difference between with and without a 80x87 can be signifigant and easily measured. But this number is much bigger (by a signifigant factor) than that even remotely possible with a more effecient 80x87. Further, in a followup post to this original, one MAY get the idea that more performance can be achieved by simply popping in a faster chip speed in a slower socket. This is NOT the case, the actual system clock speed is like a traffic cop. Everything goes that speed in that system. So, when a 100 Mhz chip is put in a 4.77 Mhz system, it will give very very very nearly exactly the exact same performance as the same model chip with a 4.77 Mhz rating. (There can be a terribly small differences but they are so small it is nearly impossible to measure.) In this case, the reference being made is to a fundamental change in chip design. This change was implemented at a higher speed rating, and is responsible for a measureable performance increase if/when that chip is used in a slower system. It also is my understanding that the redesign of the 80387 chip by intel that was implemented at the 33 Mhz speed, has been reapplied across the board to all 80387's now in porduction. Can anybody give reference to either confirm or deny that rumour ? (Anybody listening at intel ? -- I guess silence may be a answer also...) al -- Al. Michielsen, Mechanical & Aerospace Engineering, Syracuse University InterNet: amichiel@rodan.acs.syr.edu amichiel@sunrise.acs.syr.edu Bitnet: AMICHIEL@SUNRISE