Help me Understand how DDRII works.

[onefasteclipse]

Ok, I under stand how DDR works, double the data for each cycle giving you double the clock speed. example: 200mhz=400mhz FSB. But how does DDRII work? how does 133mhz give you a 533mhz fsb? Also, how is it that DDR 667 will allow for a 1066mhz fsb? thank you.

 

[1Tanker]

Ok, I under stand how DDR works, double the data for each cycle giving you double the clock speed. example: 200mhz=400mhz FSB. But how does DDRII work? how does 133mhz give you a 533mhz fsb? Also, how is it that DDR 667 will allow for a 1066mhz fsb? thank you.

DDR2 is the same as DDR. Both double data-rate. The difference is different sized memory chips, and different number of pins(DDR2=240..DDR=184). The different process technology, and PCB's allow for higher speeds to be achieved(just as a 65nm CPU theoretically can reach higher speed than at 90nm). As for 133FSB=533....that is on Intel with the quad-pumped bus. The bus does the same thing that DDR does...it transfers 4x as much data/clock cycle. DDR667 is 667/2..so it runs at 333MHz times the quad-pumped bus=1333MHz FSB. 1067 FSB is reached with DDR2-533. Kind of confusing, but i hope this helped a bit.

 

[Corasik]

On most motherboards these days memory (be it DDR, DDR2, or anything else) are 'dual channel'

Each DDR memory channel is 64bits wide, taking DDR2 533 as an example the bus runs at 266mhz, with 2x64bit transfers per cycle.

With dual channel running syncronously, then you have an effective 128bit bus, so you can now transfer 4x64bits per clock cycle.

A Pentium, or Core 2 processor has a 64bit frontside bus, running between 100mhz and 266mhz depending on the model. As its 64bit bus can do 4x64bit per clock cycle, thats why motherboards need dual channel ram to keep up.

AMD have the memory controllers built into the processor, so they have 2 64bit memory busses running at DDR rates, I dont know what clock frequency's can be selected on the AMD memory controllers.

QDR memory is in development, but I believe there are some Patent issues allow Rambus to hold up the work.

 

[onefasteclipse]

That helps alot, thanks for the info.