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DDR4 2133mhz CL13 vs 2666mhz CL15

post #1 of 7
Thread Starter 
Hi i am building an 6700k platform for gaming and I don't know which memory to pick. I have narrowed the choices to Hyper X Savage DDR4 2133mhz CL13 or 2666mhz CL15. So give the trade off of freq vs latency is there any difference here? The 2133 is actually £2 more expensive.
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post #2 of 7
How are you at math?
2133 x 15 = 31995
2666 x 13 = 34658

Memory latency, or timings, like the number 10 in CL 10, are the length of time it takes the memory to complete a step in what it has to do. That "time" is measured in "clock ticks", ie CL 10 takes 10 clock ticks to complete before the memory can move on to it's next operation. The length of one clock tick is the speed at which the memory is running. 1800 MHz memory has a clock tick length of one 1,800,000,000th of a second (1,800,000,000 clock ticks per second), so the CL step takes 10 x 1/1,800,000,000 seconds.

A stick of memory always takes the same amount of time to complete it's CL step (or any other step) no matter what speed it is running. If you run the above memory stick faster, say 2400 MHz, it still takes 10 x 1/1,800,000,000 seconds to complete the CL step, but each clock tick is now 1/2,400,000,000 of a second, so it now would take more clock ticks to complete the CL step. Namely, 24/18 times 10 (for CL step) or 13.3 clock ticks (10 times 24/18 clock ticks). But, alas, that has to be rounded to to CL 14 as memory can't use partial clock ticks..
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post #3 of 7
2666mhz CL15 is faster in everything vs 2133mhz CL13

higher bandwidth and lower latency

https://en.wikipedia.org/wiki/CAS_latency
there's a formula in that link and CAS has to be whole numbers
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post #4 of 7
Thread Starter 
Quote:
Originally Posted by billbartuska View Post

How are you at math?
2133 x 15 = 31995
2666 x 13 = 34658

Memory latency, or timings, like the number 10 in CL 10, are the length of time it takes the memory to complete a step in what it has to do. That "time" is measured in "clock ticks", ie CL 10 takes 10 clock ticks to complete before the memory can move on to it's next operation. The length of one clock tick is the speed at which the memory is running. 1800 MHz memory has a clock tick length of one 1,800,000,000th of a second (1,800,000,000 clock ticks per second), so the CL step takes 10 x 1/1,800,000,000 seconds.

A stick of memory always takes the same amount of time to complete it's CL step (or any other step) no matter what speed it is running. If you run the above memory stick faster, say 2400 MHz, it still takes 10 x 1/1,800,000,000 seconds to complete the CL step, but each clock tick is now 1/2,400,000,000 of a second, so it now would take more clock ticks to complete the CL step. Namely, 24/18 times 10 (for CL step) or 13.3 clock ticks (10 times 24/18 clock ticks). But, alas, that has to be rounded to to CL 14 as memory can't use partial clock ticks..

Thanks for the explanation, I honestly don't know much about it. But you mixed up the cl timings in your calculations, so it should read:
2133 x 13 = 27729
2666 x 15 = 39990

But what does the the outcome of the calculation signify? It can't be that the higher the number the better, because higher CL is not a positive? If you divide the freq by the CL wouldn't that give a more meaningful number like 164 to 177, as in operations over time?
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post #5 of 7
Thread Starter 
Quote:
Originally Posted by czin125 View Post

2666mhz CL15 is faster in everything vs 2133mhz CL13

higher bandwidth and lower latency

https://en.wikipedia.org/wiki/CAS_latency
there's a formula in that link and CAS has to be whole numbers

But isn't it higher frequency and higher latency. Surely cas 15 is slower than 13?
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post #6 of 7
easy way to check is if performance index and mhz is higher and the 2666 kit is higher
2666/15 = 177 and 2133/13 = 164

2x15 / 2.666 = 11.25
2x15 +3 / 2.666 = 12.37
2x15 +7 / 2.666 = 13.87

2x13 / 2.133 = 12.189
2x13 +3 / 2.133 = 13.595
2x13 +7 / 2.133 = 15.471
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post #7 of 7
Quote:
Originally Posted by Remontoire View Post

Thanks for the explanation, I honestly don't know much about it. But you mixed up the cl timings in your calculations, so it should read:
2133 x 13 = 27729
2666 x 15 = 39990
No, the calculations were not reversed. Read the post about timings and think about it.
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