A little behind the times on RAM knowledge

[mazeroth]

Right now I am running my DDR2-800 (PC 6400) RAM at 367 mhz according to my BIOS. All I did to overclock it was go into my BIOS and up my RAM speed from 200 to 367 mhz and BAM, instant + 1.5 ghz. overclock. Now, what I don't understand is how RAM is rated. Since it's DDR2-800, does that mean it's guaranteed to run at 200 mhz. which is the stock FSB, or does that guarantee that it will run at 400 mhz? I'm trying to figure this out because if it's what I think it is then my memory is technically running at DDR2-1468, right?

The reason I ask is because I was looking for RAM for my brother's new computer build and stumbled across this deal:

http://www.newegg.com/Product/...x?Item=N82E16820211066

Reading through the reviews I see people stating how they upped it to speeds such as 233 mhz. or 250 mhz, which seems pretty pathetic. He will be using an E2180 so if he went with this RAM he would only get an additional 330 - 500 mhz. if he gets the results that others are getting, right?

I apologize if I sound like an idiot but I really don't understand RAM all that well! Any help or links to educate me are greatly appreciated!

 

[DSF]

From one of my posts on the same subject:

Originally posted by: DSF
Time for the old "What does FSB really mean?" discussion.

Intel processors don't report the clock frequency of the frontside bus (FSB), they report the number of transfers/second, which is 4x higher. (In other words, the E6850 you chose makes 4 transfers per clock cycle on a 333MHz FSB, for a total of 1333.)

Similarly, RAM modules don't report the actual FSB either. They also report the number of transfers/second, but in this case, the number is only 2x higher because DDR/DDR2/DDR3 make two transfers/clock cycle. DDR2-1066 isn't running on a FSB of 1066, it's actually only rated for a FSB of 1066/2 = 533MHz. Still, this is considerably higher than any stock desktop processor requires today.

So, to recap, the true FSB speed of your E6850 is only 333MHz. This means that to match the FSB speed of the processor, you need DDR2-667. DDR2-800 is in many cases just as cheap. DDR2-667 and DDR2-800 are both fully compatible with your motherboard. DDR2-1066, since you're not overclocking, is a waste of money. Completely.[/b]

 

[sutahz]

As DSF has stated
DDR double's your FSB and Intel chips quad pump (amd is like DDR and double pumps [thats what your mom said]).

The RAM in your system can run at 400FSB, and probley higher as well.
When ppl say "upped it to speeds such as 233 mhz. or 250 mhz" they probley mean they took it from 800 to 1033-1050MHz.
Your cpu and your brother's cpu both have 200FSB's. You should buy ram based on price. Which ever 2x1 or 2x2 kit you can find for cheap (DDR667 or 800) should be your choice (cheapest brand you trust rather).

 

[BonzaiDuck]

My view on this is probably the same as everyone else's for those posting in response.

The rated speed means that the modules will run at that speed and at SPD default latencies and the stock voltages.

You can either attempt to run the RAM at a 1:1 ratio with the CPU host-frequency (which would have to be 400 Mhz to achieve DDR = 800 Mhz, or at a different divider/memory-multiplier, such as 4:5.

At 4:5, suppose you have a CPU rated at 1,066 Mhz FSB, and you over-clock to 1,333. Then the RAM would need to run at 835 Mhz (DDR) to meet that ratio.

This is useful if your motherboard or processor simply won't let you get to 400 Mhz host-frequency, and you want to run the memory at a different memory-bus speed. You'll probably break-even on benchmark scores over 1:1 at lower frequencies and tighter latencies. YOu may be able to run the memory at voltages a notch lower than you'd need with the 1:1 setting to get the same benchi-results.

As for PICKING RAM, you can HOPE that high-end, DDR2-800 or DDR2-1000 or DDR2-1066 (or whatever) will provide for really tight latencies at lower speeds and a 1:1 ratio -- for instance, you could run DDR2-800's as DDR2-667 if you OC a 1066 processor to a front-side-bus of 1,333 and the RAM is running at (DDR) 667. You might be able to use nice tight latencies to improve bandwidth at those speeds. But there's never a guarantee that those high-end RAMs can run with the lower latencies, even if there's a darn good chance of it.

Similarly, you might want to buy DDR2-667 memory and attempt to over-clock it to -- say -- 740 (DDR) Mhz, perhaps loosening the latencies a bit, even if upping the VDIMM voltage a tad (within spec -- I'd recommend). But some will . . . . . and some won't. For want of a better term, I call this "elasticity" -- low-end RAM with tight timings that can be over-clocked -- maybe at a higher VDIMM within warranty maximum spec -- and allow you to achieve a higher FSB and over-clock for your processor.

Sometimes reviews will show RAM that's been put through it's paces, and you can be sure that they have "elasticity." Other times, you may purchase high-end memory with review indications that they will run at certain tight latencies at lower FSB speeds, and it's a good gamble.

So if you buy DDR2-800's spec'd for latencies of 4,4,4,12, they're guaranteed to run at 800 with those latencies. You MIGHT be able to get them to run with timings 4,4,4,10, or even 4,3,4,9 @ 800 Mhz. You hope. You make an educated guess, that is. And they should always be able to run at DDR2-533, DDR2-667, DDR2-700 -- whatever with latencies of 4,4,4,12, while you hope that you might be able to squeeze DDR2-667 and 3,3,3,8 out of 'em. But you're not guaranteed that those tight latencies will work, either.

 

[DSF]

Originally posted by: BonzaiDuckSometimes reviews will show RAM that's been put through it's paces, and you can be sure that they have "elasticity." Other times, you may purchase high-end memory with review indications that they will run at certain tight latencies at lower FSB speeds, and it's a good gamble.

I just want to point out that overclocking always carries the caveat that "your mileage may vary." Just because one reviewer was able to acheive a certain result, on a certain motherboard, with a certain processor and power supply, doesn't necessarily mean that you'll be able to squeeze the same timings out of your sticks.