System bandwidth

[oldman420]

🙂
ddr 400 ram has a rated bandwidth of 6.4 g/s at 200 MHz.
So I have some questions.
what is the maximum bandwidth of a Barton mobile CPU at 2 ghz?
How would you do the math to estimate system bandwidth at any given fsb/multiplier?
Why is it that I according to benchmarks can never reach 6.4 g/s in my system even overclocked?
Thanks
:beer:

 

[otispunkmeyer]

ok the 6.4gb you are refering too is for a dual channel configuration IIRC
also i think ddr400 is needed if you are wanting to reach the max bandwidth

IIRC athlon xp maxes out at 3.2gb/s on VIA and altho the nforce 2 is dual channel i still dont think the athlon xp can muster much more than 3.2 but im not sure

as a rule if u increase the FSB (ie you are increasing the system speed) you will increase bandwidth

for example for a 2.4ghz processor u could run 200x12, but it would be better to run 240x10, since tyou have the same cpu speed yet more badwidth because the system speed has been increased.


as for the math im not too sure...i ususally rely on sis soft sandra to tell me,

also if they say its rated at what ever speed...in real terms they dont quite max out. like in graphics cards...the peak fill rate is such n such but in real terms that fill rate is never reached coz its all theoretical

 

[Sunner]

DDR DIMM's are 64 bits wide, giving 3.2 GB/Sec, P4's with i865 or better chipsets use two channels, so with 2 64bit wide channels you end up with 6.4 GB/Sec.
This is with 200 MHz modules of course.

All AthonXP's use a 64bit system bus, so no matter the memory bus, you're gonna be limited to bus freq * 64 bits of throughput, hence for a Barton with a 200 MHz DDR bus you'll be limited to 3.2 GB/Sec no matter what memory configuration you have.

And you'll never reach that in the real world, all those numbers are theoretical.