motherboard/CPU FSB speed sync with DDR2
Posted on 2007-04-02
Hi can anyone help clarify how DDR2 RAM speeds work with CPU / motherboard FSB Speeds.
First of all i am from the background of matching your CPU FSB speed with your RAM speed.
So I would buy a motherboard that supported for example 266MHZ fsb, an AMD CPU with an FSb of 266MHZ and DDR 266MHZ.
Same for the AMD boards / CPU that supported 400MHZ FSB.
Now with Intel I know they were slightly different to AMD in that they if you had an FSB of 800MHZ , you used a CPU with 800MHZ FSB and DDR400 since ram ,
This worked because the true CPU FSB was 200 x 4 = 800MHZ and the true speed of DDR 400 was 200 x2!
Because the base frequency of both the RAM & FSB before multiplication was 200MHz sync / speed matching was possible.
I also have an intel based laptop which follows the same theory , FSB of 533 and uses DDR266, again following the same rule that DDRR266 is 2 x 133MHZ and 533 fsb is 4 x 133.
Ok with DDR2 memory i have seen intel cpu / motherboards specifying an FSB of 800 to be used with DDR2 533!
now the equal multipuls / sync dosen't work?
by using the old formula now we have a true FSB before multiplication of 200 with ram speed of 266 before multiplication. So does that mean the ram is being under clocked?? also some boards state ddr2 667
I've also seen intel fsb of 1066 used with 533 ram which does seen to fit with true sync/ the old formular.
With AMD am2 boards im seeing FSB of 1000mhz used with DDR2 800 or 667 or 533,
none of these ddr speeds match the 1000MHZ fsb , so how is syn acheived and which ram do you use ??
I was also told that because of AMD hyper transport bus that speed match of FSB / RAM was required anymore because the ram would work at its rated speed?? is this true ?
So you could have an FSB of 1000MHZ with DDR2 533??
Can anyone help clarify how these new FSB / ddr configurations work?? for both AMD an intel