Memory: 800MHz vs 667MHz

[mshepp]

Is there much difference between memory running at 667MHz and that running at 800MHz? Assuming both memory modules are Dual Channel DDR2 SDRAM.

Thanks

[gwai lo]

66/67 MHz difference...

What exactly do you mean? or what exactly are you getting at?

[mshepp]

Difference in performance, i mean is it worth paying an extra ?30 to get memory that runs at 800MHz.

[Tikimotel]

That all depends on what hardware you will be using it with...

Buying 800Mhz DDR2 and your hardware doesn't support this speedrating, it's a waste of money...

[gwai lo]

Depends on your situation, okay I think I have an idea of what you're thinking about, so I'll try to explain.

Processor clock speed is determined by this simple equation: frontside bus ? multiplier = clock speed ( e.g. 333?9 = 2997 MHz )

Now in order to "get the most out of your system" without overclocking, you need RAM that has the ability to at least match that frontside bus speed. In this case that's 333?2double/b> data rate ) = DDR2-667 or ( 8 bits in a byte ) PC2-5300/5400. That's all you need, if you get RAM faster than that the RAM will only run at the speed that you define it to run at or the slowest running component. In the case of a stock system, the lowest common denominator is the frontside bus of 333 MHz. If you get anything faster, it'll still only run at that speed until you tell it otherwise either via overclocking or running a ratio that will set RAM to run faster than the FSB ( e.g. 2:1 where the RAM runs twice as fast as the FSB ).

So anything faster than what you need is essentially wasted. In this specific situation, there are no chips that have stock FSBes of 400 MHz, so buying DDR2-800 results in a wasted 66/67 MHz unless you're overclocking ( as the fastest FSB is 333 MHz ).

edit: Oh i forgot, there is the whole latency difference possibility. RAM that has been binned to run at higher frequencies is usually strong enough to run tighter timings at lower frequencies when compared to RAM that's rated for lower frequencies. Thus, there might be a performance difference resulting from the timing difference...but it's not significant in our current systems.

Edited January 19, 2008 by gwai lo

[Tikimotel]

If you are using a Intel core duo proc. It won't make much real-life difference.

Synthetic benchies maybe, but in the end the apps perform on par.

Try looking (google) for older reviews on the core duo performance, and memory latency.

[Impact]

@ Tikimotel: It most likely supports it and that's why he's asking the question :rolleyes: Edit: Sorry, a couple posts late.

I don't think you will be able to tell much of a difference.

[Yusuf M. Veteran]

Wow +gwai lo, I didn't know that. Thanks for the information! :D

[gwai lo]

Yep, no problem, I was kind of worried that it might not make any sense to anyone else. =|

[Impact]

It made sense and thanks for the nice and long explanation! You are really good at explaining things.