From: jmthill AT earthling DOT net (Michel Thill)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Speed problems with AMD K6
Date: Wed, 21 Jan 1998 16:46:31 GMT
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On Tue, 20 Jan 1998 02:49:35 GMT, Elliott Oti
<e DOT oti AT stud DOT warande DOT ruu DOT nl> wrote:

>Gary Smith wrote:
>> 
>> Help..
>> 
>> I have just changed my CPU from a Cyrix 6x86 P166+ to an AMD K6 166MHz, and
>> have noticed a drop in performance with programmes written using using DJGPP
>> and Allegro.  The drop in performance is in the region of 20%.
>> 
>> I have benchmarked the AMD and the Cyrix using Wintune 97, and in all the
>> tests the AMD is faster than the Cyrix. eg:
>> 
>> Floating Point Performance (MFLOPS)
>> -------------------------------------------------------
>> AMD K6 P166               98
>> Cyrix 6x86 P166+          52
>> 
>> Integer Performance  (MIPS)
>> -----------------------------------------
>> AMD K6 P166               320
>> Cyrix 6x86 P166+          250
>> 
>> Does anyone have any ideas as to the cause of the performance drop with the
>> AMD CPU ?
>
>Could be the system bus clock speed. What speed is it running at? For
>instance, I have a AMD 486 DX4-100 ( bus speed 33 MHz) and a Cyrix 486
>DX2-80 ( bus speed 40 MHz), and the DX2-80 blits consistently faster
>than the DX4-100, despite its slower CPU ( the rest of the hardware is
>identical). I don't know what speed the AMD and Cyrix boards are
>_really_ running at ( I think the Cyrix 166+ runs at 133 MHz, with a 66
>MHz bus clock; could be the AMD system bus runs at 40Mhz ). It could

K6 (166,200,233) runs at 66 MHZ bus clock.
The AMD 486 dx2-80 ran at 40 MHZ bus clock.

>simply be that Cyrix motherboards have better buses than AMD. 
>
>Then again, it could be a software problem; are you running your djgpp
>progs under a different DPMI host on the AMD than on the Cyrix?