DDR2 memory clock vs cpu base clock - Page 2 - Overclock.net

IwubAMD · 05-04-07

Quote:

Originally Posted by thealmightyone

Yeah, it seems that the memory controller for AM2 has a thing with funny CPU multipliers. It all confuses me a bit, to be honest. Well, not confusion, I'm just too lazy to see how everything works.

i dont think it has to do with just odd multipliers though as the even multipliers are going by it the same way, it just happens that the end results correlate with the bus speed

Cheetos316 · 05-06-07

Because the memory bus is independent from the Hypertransport bus, the memory speed is not directly determined by the speed of the base Hypertransport frequency. The memory controller runs at the full speed of the chip and then puts a divider in for the memory thus the memory frequency is determined by the chip frequency. But also keep in mind that the base Hypertransport frequency does affect the core speed as well.

Where does that bring us? In a full circle.... This is the extent I know. Hope we get some great info out of this thread!

IwubAMD · 05-06-07

Quote:

Originally Posted by Cheetos316

Because the memory bus is independent from the Hypertransport bus, the memory speed is not directly determined by the speed of the base Hypertransport frequency. The memory controller runs at the full speed of the chip and then puts a divider in for the memory thus the memory frequency is determined by the chip frequency. But also keep in mind that the base Hypertransport frequency does affect the core speed as well.

Where does that bring us? In a full circle.... This is the extent I know. Hope we get some great info out of this thread!

can you elaborate on the bolded? core speed of the CPU right?

and if the memory controller runs at the full speed of the CPU, then the cpu will not be waiting for the memory at all (like it would if you ran your ddr @ 266 w/ a 200mhz cpu )? thats what that seems to indicate

i think this is very interesting since like i mentioned before ram was(?!) the only component directly related to the bus anymore

also if all this is true, isnt that a pretty huge leg up over intel?

**The Duke** · 05-06-07

Quote:

Originally Posted by IwubAMD

you guys say that and it makes sense, but why does the chart in the sticky http://i147.photobucket.com/albums/r...337/DDR2_2.jpg

show in the last table that 200mhz fsb on the cpu yields 750 as an effective rate for ddr2 800

according to that, and a few other places ive read are pointing to the ram speed being determined by the CPU final clock and not directly the fsb

also thealmighty one, i was under the impression that ddr2 transfered 2 bits per hert just like DDR, using the same memory speed, but double the bus speed IE 200mhz memory speed x 2 at a time = a 400mhz actuall bus speed x2 bits per clock for an effective speed of 800

CPU bus speed and RAM speed.
Yes, the CPU can effect the RAMs overall speed in that....
The RAMs divider and CPU multiplyer complicates the out come.
An easy to grasp factor... just dubble the overall for DDR2
CPU @ 250 MHZ and RAM @ 1/2 or 100MHz or DDR200 speeds.
Not only does the RAM start at 1/2 the speed but basically (CPU multiplyer dependant) the RAM only increases 1/2 MHz for every 1MHz the CPU bus speed is increases. So in that case, generally, the RAM would have a base speed of 125MHz or a 25MHz increase relative to the CPUs 50MHz increase.
Again, that is a reasonable generalization based upon basics, the effects change with the CPU multiplyer and the RAM to CPU ratio, furthermore, CPU 1/2 multiplyers only effect the CPU and not the RAM since the memory controler only utilizes whole integers.

newt111 · 05-06-07

Quote:

Originally Posted by The Duke

CPU bus speed and RAM speed.
Yes, the CPU can effect the RAMs overall speed in that....
The RAMs divider and CPU multiplyer complicates the out come.
An easy to grasp factor... just dubble the overall for DDR2
CPU @ 250 MHZ and RAM @ 1/2 or 100MHz or DDR200 speeds.
Not only does the RAM start at 1/2 the speed but basically (CPU multiplyer dependant) the RAM only increases 1/2 MHz for every 1MHz the CPU bus speed is increases. So in that case, generally, the RAM would have a base speed of 125MHz or a 25MHz increase relative to the CPUs 50MHz increase.
Again, that is a reasonable generalization based upon basics, the effects change with the CPU multiplyer and the RAM to CPU ratio, furthermore, CPU 1/2 multiplyers only effect the CPU and not the RAM since the memory controler only utilizes whole integers.

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DDR2 memory clock vs cpu base clock

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