sek9424@cec1.wustl.edu (Scott Eric Keller) (03/12/90)
I am currently trying to determine what real differences there
may be between 10Mhz and 12.5Mhz '286 machines. I currently have a
Compuadd 286-10 using a 10Mhz '286 processor with 1 wait state and 100ns
RAM. This machine produces a 9.7Mhz clock rate on both the Lanmark CPU test
and the PC Tech Journal ATPERF performance test. Out of curiosity, I tried
operating the machine with 0 wait states. After a few memory errors at
power on, the machine will operate for several minutes at 12.7Mhz indicated
by the Lanmark test. The ATPERF test still shows 9.7.(why?) Eventually this
configuration locks up. This is really no surprise since the processor is
more than 25% over speed.
My questions are as follows.....
1) Can the 10Mhz '286 be replaced with a 12.5Mhz '286 more or less directly?
Note that the only 2 crystals in the machine are one of the colorburst
variety and another which says 12Mhz. I have reason to suspect that the
10 and 12.5 boards may be one and the same.
2) If the above is affirmative, will anything else have to change. (i.e.
RAM, clock crystal, etc.) I believe 100ns RAM should be fast enough.
3) Is there a reason for the wait state other than keeping the processor
happy? Or is it needed to slow down to keep the memory happy? What is
it we are all 'waiting' for?
I realize this may not work, but given the fact that a 30% increase
in speed could theoretically be had for ~$60 for a new processor I would
certainly consider it. I would appreciate any information you can offer.
Scott
--
Scott Keller (KA0WCH) - Permanent Undergrad - Dept. of Computer Science
Wa$hington Univer$ity - St. Louis, Mo. USA
Internet: sek9424@cec2.wustl.edu UUCP:ihnp4!wucec2!sek9424 (I think...)
The opinions represented here are mine and mine alone, not Wa$h. U's.Ralf.Brown@B.GP.CS.CMU.EDU (03/12/90)
In article <1990Mar12.040128.3975@cec1.wustl.edu>, sek9424@cec1.wustl.edu (Scott Eric Keller) wrote: } } I am currently trying to determine what real differences there }may be between 10Mhz and 12.5Mhz '286 machines. I currently have a }Compuadd 286-10 using a 10Mhz '286 processor with 1 wait state and 100ns }RAM. This machine produces a 9.7Mhz clock rate on both the Lanmark CPU test }and the PC Tech Journal ATPERF performance test. Out of curiosity, I tried }operating the machine with 0 wait states. After a few memory errors at }power on, the machine will operate for several minutes at 12.7Mhz indicated }by the Lanmark test. The ATPERF test still shows 9.7.(why?) Eventually this Because ATPERF computes the actual speed of the clock signal fed to the processor, while Landmark and all other benchmarks I know of compute the "effective throughput" which is good for advertising but not much else. Landmark is telling you that 9.7MHz at 0 waits is equivalent to 12.7MHz at one wait state. }3) Is there a reason for the wait state other than keeping the processor } happy? Or is it needed to slow down to keep the memory happy? What is } it we are all 'waiting' for? It is needed to slow down memory accesses enough for the RAM to keep up. Note that 100ns RAMs *should* be fast enough for zero waits at 10MHz (I used to have a 9.8 MHz/1ws machine that ran just fine with 150ns RAMs--the wait state increases the allowable access time on the RAMs by 50%) -- UUCP: {ucbvax,harvard}!cs.cmu.edu!ralf -=- 412-268-3053 (school) -=- FAX: ask ARPA: ralf@cs.cmu.edu BIT: ralf%cs.cmu.edu@CMUCCVMA FIDO: Ralf Brown 1:129/46 "How to Prove It" by Dana Angluin Disclaimer? I claimed something? 16. proof by cosmology: The negation of the proposition is unimaginable or meaningless. Popular for proofs of the existence of God.
cs4g6ag@maccs.dcss.mcmaster.ca (Stephen M. Dunn) (03/16/90)
In article <25fb9dc7@ralf> Ralf.Brown@B.GP.CS.CMU.EDU writes:
$Because ATPERF computes the actual speed of the clock signal fed to the
$processor, while Landmark and all other benchmarks I know of compute the
$"effective throughput" which is good for advertising but not much else.
I can't agree with you on that. Personally, I couldn't care less what
the actual clock speed of my machine is; it's the performance that counts,
and that's what ATPERF does _not_ measure! Given the choice between a
20 MHz 80286 with a disgusting memory subsystem that gives 10 MHz throughput
and a 12 MHz 80286 with 0 wait states that gives 13 or 14 MHz throughput,
I want the 12 MHz system because it works faster, not the 20 MHz one because
its crystal runs at a higher frequency. (Okay, so I'm exaggerating, but
you get the idea).
--
Stephen M. Dunn cs4g6ag@maccs.dcss.mcmaster.ca
<std_disclaimer.h> = "\nI'm only an undergraduate!!!\n";
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"So sorry, I never meant to break your heart ... but you broke mine."