What are the effects of using 800Mhz RAM with a 1066Mhz FSB CPU?

I'm just wondering what happens when you use 800Mhz DDR2 RAM in a system with a Core 2 CPU that has a 1066 FSB? Will the performance be *seriously* affected? Or is it rather negligible? My system is not for gaming, it's for video editing and the RAM mostly holds cached history states for the artwork/videos that I'm working on.

The lowest common multiplier for 800 and 1066 would be 426400. So does that mean it takes the RAM 533 cycles to sync up with the CPU? Surely that doesn't mean that the CPU has to wait 533 cycles before it can speak to the RAM, does it?

If there is a major slowdown caused by using 800Mhz RAM.. perhaps I should get 533Mhz instead?

 

TBH, I didnt try to comprehend the cycle thing, and common multipliers etc. But DDR2-800 is the fastest DDR2 SODIMM available, and they're pretty cheap as well (at least in the US).

The FSB and CPU will remain unaffected by the frequency of the RAM, but since you do alot of memory-intensive work, its better to get the fastest RAM possible (and well-priced as well ). The memory multiplier will be set automatically depending upon the memory and FSB clocks.

 

Actually, since I do a lot of memory intensive work I thought it was understood that more RAM is better than faster RAM.

The only important spec for RAM when it comes to design work/video editing is simply the interface speed... which is 6.4GBps. That is way way more than enough to stream the history states fluidly onto my screen. I don't need any additional bandwidth offered by DDR3 and I most definitely do not need the higher frequency or the higher costs associated with it.

What I'm concerned about is how significantly performance is affected when the FSB and RAM clocks to not multiply together easily. I would downgrade to 533 Mhz before ever considering 1066 Mhz DDR3.

 

The FSB and CPU (performance) will remain unaffected by the frequency/clocks of the RAM.
There is no need for FSB and RAM clocks to multiply with each other easily or the memory multiplier to be a whole number.

And you cannot consider DDR3 modules anyway, if your motherboard has DDR2 connectors.

EDIT: Oh, my bad. I probably misinterpreted the OP's question.

 

Andy, you did not answer his question....

Answer - No, there will be no slowdowns due to 800mhz ram as long as you use dual channel mode. As long as you surpass the fsb speed you are fine. 800mhz in dual channel is like 1600fsb speed.

 

The CPU FSB bandwidth is not as great as the memory bandwidth, so you will be fine (increasing the memory bandwidth would not yield any performance difference).

 

For 1066MHz FSB and 667MHz RAM
Memory Latency (Dual DDR2-667 5-5-5-15): 84.6 ns [calculated by Everest 5.02 however it does it ..beats me how this timing stuff works]



From Everest 5.02
RAM Read Speed: 5939MB/s
Write Speed: 5530 MB/s
Copy Speed: 4203MB/s

RAM single-channel theoretical bandwidth: 5333MB/s
FSB theoretical bandwidth: 8533MB/s
RAM dual-channel theoretical bandwidth: 10667MB/s

 

NO Dual channel mode does not double the frequency...

Anywayz this is why you shouldnt have any problems..
First of all your memory is DDR(2) so its actuall frequency/clock is 800mhz/2..but since it can receive/send data on both pos and neg edge of clock the manufcatures for simplicities sake just say the frequency/clock has been doubled to 800mhz.
Your FSB is Quad Pumped so its actual frequeny is 1066/4=266mhz

So you see your memory clock is actually faster than your FSB, but because the FSB can sent/recieve data four times in one clock cycle it still works faster. i.e it can send/recieve data faster

Still these different frequency/clock speeds have to be interfaced. A chip on your motherboard located between the CPU and ram, interfaces the two.Its called the northbridge(it is part of the "chipset"...but thats not important). Between The CPU and nothrbidge is the FSB, and between the northbridge and memory is the memory bus. The northbridge will take care of the delays and such associated with both.

The northbridge determines what kinda memory and cpu is supported by ur motherboard(Also depends on motherboards socket)...So you have to make sure your chipset supports DDR2 800.

Btw dual channel simply doubled the memory bus, from DDR2's 64bit to 128 bit if im not mistaken.

 

Well I guess that settles it. Thanks guys. Good explanation, BigBird.

And yes, my lappy will use DDR2 and it does not support DDR3, so I'm okay there.

I didn't realize that the theoretical bandwidth for DDR2 was over 10GBps! Cool.

 

Keep in mind the chipset you are using might have a 1066MHz FSB for the processor, but might only support 800MHz SODIMMs; so even buying faster RAM will simply mean it is downclocked anyway.