Displayed Clockspeed vs Actual Clock speed

Discussion in 'Memory' started by AnAngelsDeath, Nov 15, 2018.

  1. AnAngelsDeath

    AnAngelsDeath Gawd

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    So I’ve been building Custom PC’s and what not since I was 15 (32 now) but one thing I never really learned about for some reason is RAM timings.

    Well I was just reading this article and it mentioned that your RAM actually only runs at half of the advertised clock speed. Thus DDR4 3000 will only run at 1500. I never heard this before. At least not that I can recall. Why does it run at half the speed they advertise it as? Why don’t they just say they actual speed ? Or is it saying that 3000Mhz would be the maximum clock speed the module is capable of, but overclocking would be required to reach it. So it just runs at 1500Mhz at stock settings ?
     
  2. cyberguyz

    cyberguyz Gawd

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    DDR4 = Double Data Rate v4.

    The double data rate means that. The memory effective speed is double of its actual clock speed (data moves on both the rising and trailing edge of each bus cycle). Thus you will see memory at ddr4 3200 running at 1600mhz bus speed.
     
  3. dasa

    dasa Limp Gawd

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    As for timings
    2000MHz RAM running c20 would have a similar latency to 1000MHz RAM running c10 but the first would have much higher bandwidth.
    For a lot of software latency is more important than bandwidth but bandwidth still helps a bit.
     
  4. pitingres

    pitingres n00bie

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    RAM doesn't, or at least shouldn't, have an advertised clock speed. It has an advertised transfer rate, which isn't the same thing. As pointed out already, DDR memory gets 2 transfers per clock, so DDR-3000 RAM is getting 3000 MT/s (not MHz) running at a clock speed of 1500 MHz.

    Unfortunately it seems that even the RAM manufacturers have given up on proper terminology, so we see nonsensical statements about "3200 MHz" RAM. Which doesn't exist. 3200 MT/s RAM, certainly.
     
  5. doublejack

    doublejack Limp Gawd

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    This situation is even worse when it comes to graphics cards. For example, my RX 580 was sold with "8000 MHz" GDDR5 memory that in reality runs at 2000 MHz. It is quad pumped, so not double data rate. The name and speed that it is sold at is very confusing to average consumers. It should be called something like GQDR5 2000 MHz.
     
  6. doubletake

    doubletake Gawd

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    Even worse than that; you're off by one step. The actual command clock is half of that, so it's actually 1000MHz memory :U
     
  7. pitingres

    pitingres n00bie

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    I've no issue with advertising a transter rate, as that's the interesting bit. What puzzles me is why manufacturers and the rest seem to be so terrified of using MT/s (million transfers/second) in performance specs. Even if you've never heard of an MT/s it shouldn't be too hard to figure out. MHz is by definition a clock rate and shouldn't be used for numbers that aren't clock rates.
     
  8. cyberguyz

    cyberguyz Gawd

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    Probably because more average computer users are more familiar with the term Mhz rather than MT/s. The marketing boffins find they can relate to more people by making them believe their memory runs at the transfer rated speed. It is simply marketing laziness in failing to educate their consumers that MT/s is not the same as Mhz, but a byproduct of it.