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I've been looking over RAM timings today, and one thing I noticed is that, even when considering very high-end DDR4 RAM, the timings are absolutely massive compared to DDR3 - I can buy very cheap DDR3 RAM with 9-9-9-24 timing, but DDR4 RAM (at nearly ten times the cost) might have a timing of 19-24-24-46. I have two questions about this:

  1. Why are the timings so much higher in DDR4?
  2. Does the speed of DDR4 ram overcome the massive timing increases?
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  • they aren't actually slower, the number is just larger. Timings are in clock ticks, which are the period of time that it takes for a single cycle in the frequency. a 1GHz tick is 1 1 billionth of a second. a 2GHz tick is half that (0.5 billionths). so as the frequency goes up, the tick time goes down, so the timing figures take more ticks to do a task, but a tick is a smaller period of time.
    – Frank Thomas
    Commented Oct 7, 2016 at 21:39
  • See the answer here about how timings can be calculated in Seconds of time, to allow an apples to apples comparisons: superuser.com/questions/593772/…
    – Frank Thomas
    Commented Oct 7, 2016 at 21:42
  • @FrankThomas so basically, the DDR4 RAM has such a high clock speed, the timings still come out to a smaller number of nanoseconds? That makes sense. I'll start applying that formula. thanks.
    – Kulahan
    Commented Oct 7, 2016 at 21:52
  • yeah, in this case the DDR4 has a frequency of 2.625 times that of the DDR3, so I'm pretty sure the numbers will work our favorably for it, though I haven't crunched the numbers.
    – Frank Thomas
    Commented Oct 7, 2016 at 21:54
  • you can almost assume that because the timing values are not quite at 2.5x of the DDR3, that the operations will be faster, if only marginally. as long as the frequency and datatransfer rate are higher, you are getting the value from the upgrade, as long as the timings are not proportionally worse. in fact, it may be worth it even if the timings are just a hair slower (proportionately) anyway.
    – Frank Thomas
    Commented Oct 7, 2016 at 22:00

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1600MHz  9-9-9-24       1.25e-9 seconds per clock tick
CL = (1.25e-9 * 9)   =  1.125e-8 seconds
RtC = (1.25e-9 * 9)  =  1.125e-8 seconds
RtP = (1.25e-9 * 9)  =  1.125e-8 seconds
tRAS =(1.25e-9 * 24) =  3.0e-8 seconds

4266MHz 19-24-24-46     4.688e-10 seconds per clock tick
CL =  (4.688e-10 * 19)  = 8.907e-9 seconds
RtC = (4.688e-10 * 24)  = 1.125e-8 seconds
RtP = (4.688e-10 * 24)  = 1.125e-8 seconds
tRAS = (4.688e-10 * 46) = 2.156e-8 seconds

So on timings, the DDR4 is the clear winner, being at worst equal to the DDR3 latencies, and at best is in an different order of magnitude.

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    Little bit of an apples to oranges comparison there: you are comparing the highest clocked DDR4 with "normal" clock, high latency DDR3. Compare it with CL6 DDR3 and the latency is worse for DDR4, even at that max clock rate.
    – psusi
    Commented Oct 8, 2016 at 1:08
  • those are the models that the OP indicated in their links. I agree it is comparing extremes, and you are quite right that you need to exceed more than 2x frequency, or you may be suffering a hit on latency when all else is equal, but for the specific models the op indicated, the ddr4 has the advantage. I do wonder if they have a CPU/board that will support RAM at that speed, but that is not part of the post.
    – Frank Thomas
    Commented Oct 8, 2016 at 2:05

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