ray@ole.UUCP (Ray Berry) (02/24/91)
sreese@slate.mines.colorado.edu (L. Scott Reese) writes: >20MHz machine and have a couple of questions: Is it possible to >use a slower speed math chip (ie. 16 MHz)? I have heard it is but >get strange responses when I say that I want a 16MHz chip for my >20MHz machine. Technically they don't have to run at the same speed. However, most motherboards only support synchronous operation (same speed). Your MB manual or vendor should have an answer on this. > Is there a major difference between the Intel 80387 and other >math chips? I am mainly wanting to use the chip for Acad 10 and >intensive graphing routines. Cyrix chips are the fastest (~2x Intel) but since a very small percentage of clock cycles are FPU instructions, in practice it really doesn't matter too much. I suggest you use whatever you can get at the best price. -- Ray Berry kb7ht uucp: ...sumax!ole!ray CIS: 73407,3152 /* "inquire within" */
poffen@sj.ate.slb.com (Russ Poffenberger) (02/27/91)
In article <84380001@hpfcmdd.hp.com> edm@hpfcmdd.hp.com (Ed Moore) writes: >The MHz rating on an 80387 chip is the speed at which Intel certifies it >will run. If you put a 16 MHz chip into a 20 MHz computer, the clock in the >computer forces the chip to run at 20 MHz. That should work _most_ of the >time. But if Intel's testing could certify the chip at 20 MHz they would >have sold it as a 20 MHz chip; something didn't work right some of the time. This isn't necessarily true. What a vendor certifies as a particular speed rating on a chip make be because of several factors. Some chip designs are rated up to a certain speed. An example is the 80386/33 which is a different chip altogether than slower versions. (not by logic design, but chip geometries such as the die shrink size.) Another factor is the packaging. Higher speed generates more heat. Some packaging is not certified to dissipate enough heat at higher speeds. Even for identical chips/packaging, vendors will sometime test chips up to a certain speed based only on market demand at the time. If they are short on 25Mhz versions, they will test only to 25Mhz, and not spend the extra time or effort to certify them to a higher speed, even though they may work. Russ Poffenberger DOMAIN: poffen@sj.ate.slb.com Schlumberger Technologies UUCP: {uunet,decwrl,amdahl}!sjsca4!poffen 1601 Technology Drive CIS: 72401,276 San Jose, Ca. 95110 (408)437-5254
v087mxgb@ubvmsa.cc.buffalo.edu (Shawn E Thompson) (02/27/91)
In article <1991Feb26.201401.22738@sj.ate.slb.com>, poffen@sj.ate.slb.com (Russ Poffenberger) writes... >In article <84380001@hpfcmdd.hp.com> edm@hpfcmdd.hp.com (Ed Moore) writes: >>The MHz rating on an 80387 chip is the speed at which Intel certifies it >>will run. If you put a 16 MHz chip into a 20 MHz computer, the clock in the >>computer forces the chip to run at 20 MHz. That should work _most_ of the >1601 Technology Drive CIS: 72401,276 >San Jose, Ca. 95110 (408)437-5254 This may be true, but in direct answer to my original question: I have learned that the 286 chip uses a 1/2 clock speed divide (meaning it operates at a sub-scalar speed of .5 of the clock cycle speed. The 287 chip operates at 1/3 the clock speed. Heat is a factor, but my question, answered by many (thanks!) was the above 2/3 ratio. st