DDR3 Timing v Clock

[Doldrim]

Having done some reading, I can see that there is a trade off between tight timings and higher clocks on the DDR3 memory. I've noticed that with quite a few pieces of RAM such as the Kingston HyperX and the GSkill that I might see something along the lines of PC2000 @9-9-9 and PC1600 @ 7-7-7 for about the same price (within $10-$20). As a result, I had a few questions.

I plan to overclock a i7 930 to some high clocks (4ghz+) and need to choose the ram for it. It's my understanding that I will not be able to use the full 2000mhz bandwidth, so is it possible to underclock 2000mhz RAM at maybe 1600mhz and achieve better timings at a lower voltage? Would this be the same as simply buying the ram at that clock/latency to begin with?

My question is a result of seeing quite a few newegg reviews where someone bought ram that was rated for 1600mhz and could barely get it to that clock with the rated latencies. I'm thinking if I bought higher rated ram i could underclock it and achieve the result with no issue.

I also would like to ask if the timing/clock is that big of an issue. Is a lose timing of 9-9-9 at a higher clock going to be faster?

As you may be able to tell, I'm still a bit confused about this stuff (overclocks used to be so simple). Any help would be appreciated.

 

[SunSamurai]

I was just about to make a new thread about this.

I have DDR3 rated at 777@ 1033. I have it at 777 t2@1220 currently and I can OC it to 1450~ with 999t1 timings and im wondering if that would be better?

To the OP, it depends on the RAM. usually you can UC your RAM and tighten the timings if its quality RAM. Not sure about voltage.

Hopefully someone can shed some light on this issue for us.

 

[EarthwormJim]

It depends on if the program you are using prefers faster access times or more bandwidth.

timings are in clock cycles, not absolute time. To get absolute time, multiple the inverse of the command rate clock freqency of the memory by the timing.

e.g.
DDR3 @1220mhz has a command rate of 610mhz
7*(610x10^6)^-1 = ~11.4ns
9*(725x10^6)^-1 = ~12.4ns

So for your CAS latency you access the first word about 10% slower but you gain almost 20% more bandwidth going from 1220mhz to 1450mhz.

If you could do a CAS of 8 @ 1450mhz, you could have faster access times AND more memory bandwidth than a CAS of 7 @ 1220mhz

Command rate is the number of clock cycles it takes the controller to find memory bank. Once it's found the bank, it doesn't have to wait those clock cycles again. Since memory is now nearly in the gigahertz range, going from a 1T to a 2T isn't as big of a deal compared to the other timings.

Tweaking memory doesn't really bring that big of a gain anyway besides in synthetic benchmarks. The only real world application that sees big gains in memory tweaking is winrar (or other compression programs).

Above all else, make sure your memory is stable.

 

[SunSamurai]

Thanks Jim, very informative!