[Tutorial] GPU Tools and GPU Memory Clock: Real and Effective Speeds Demystified



GPU Tools and GPU Memory Clock: Real and Effective Speeds Demystified


I recently received this strange image of a GTX 480 tortured by FurMark.

FurMark and an overclocked EVGA GTX 480 - Temperature spikes
FurMark and an overclocked EVGA GTX 480 – Temperature spikes


Hummm tortured is not really appropriate if we look at the current intensity and GPU power: 27A and 29W… And the FPS: 34 FPS is too low for a GTX 480 even with MSAA enabled. I think the system has a problem (look at the nice temperature spikes – may come from a bug in GPU-Z, I don’t know) but don’t ask me what’s kid of prob 😉

But that’s not the point!

The guy who sent the image asked me why the memory clock of his GTX 480 is 950MHz instead of 1900Mhz. If we look at the image, we see that GPU-Z is used to monitoring the clocks and temperature.

GPU-Z displays the real memory clock frequency or memory speed which is 950MHz (this is an overclocked memory since the stock speed of a GTX 480 is 924MHz). The real memory speed is the most important information. All other values you can read in other GPU tools or graphics cards reviews are the effective speed which depends on the type of memory (GDDR3, GDDR5) and people who have witten the specs, the reviews or the GPU tools 😉

Roughly said, there are 2 kinds of graphics memory currently in use: DDR (Double Data Rate) and QDR (Quad Data Rate or Quad-pumped). For example, the GDDR3 memory (on GTX 200 for example) is a DDR memory while the GDDR5 (on HD 5000 or GTX 400) is a QDR memory.

The effective speed of a DDR memory is:

DDR_effective_speed = real_speed x 2  

And the effective speed of a QDR memory is:

QDR_effective_speed = real_speed x 4  

Then for a GTX 480 (GDDR5) with stock memory speed we have:
– Real memory speed: 924MHz
– Effective DDR memory speed: 1848MHz
– Effective QDR memory speed: 3696MHz

For a HD 5870 (also GDDR5) we have:
– Real memory speed: 1200MHz
– Effective DDR memory speed: 2400MHz
– Effective QDR memory speed: 4800MHz

And for a GTX 275 (GDDR3) we have:
– Real memory speed: 567MHz
– Effective DDR memory speed: 1134MHz

IN practice, very often, the DDR speed is used in the specs of GDDR5 memory. For exemple, NVIDIA displays the effective memory speed of the GTX 480 as a DDR speed (1848MHz) instead of a QDR speed (3696MHz) (see specicifications HERE).

And what kind of speed is displayed in our GPU tools ?

As we said, GPU-Z displays the real clock speed. EVGA Precision, MSI Afterburner
or the new GPU Shark display the effective DDR speed:

GPU-Z
GPU-Z shows real memory speed


EVGA Precision
EVGA Precision shows DDR memory speed


GPU Shark
GPU Shark shows DDR memory speed

I hope the memory speed you see in graphics cards reviews or in your favorite GPU tool is clear now.



References



21 thoughts on “[Tutorial] GPU Tools and GPU Memory Clock: Real and Effective Speeds Demystified”

  1. WacKEDmaN

    nice write up..

    as for the anomoly is in the pic..ive has some issues like that. Usually caused by the driver getting stuck in a lower power state. P8 or P3 instead of P0.

    usually fixed by a reboot, or disabling the card in device manager then re-enabling it (only if you have a 2nd card installed!)

  2. WacKEDmaN

    i should also say that when this stuck low power mode is in play CPU-Z still reports the P0 state and full speed core and memory values.

    seting the clocks via MSI-Afterburner while in this stuck low power state will NOT reset the clocks, but it does show the correct core/mem values (the P3 state for me running 2 monitors. running one monitor, ive had it get stuck in P8 and even P12)

    the cause of it getting stuck.. for me it happens mainly when a compute app crashes (eg CUDA, OpenCL, DirectCompute, or even PhysX) ..but not always

  3. WacKEDmaN

    for those who still cant get their head around the real vs effective speeds, think of it like this.

    the real memory speed is the clock speed that is sent to the memory chips via a clock generator of some sort

    the effective speed is the internal clock speed running inside the memory chips, which is either double pumped (DDR) or quad pumped (QDR) over the ‘real’ clock

    basically.. for every ‘tick’ of the clock, the memory can perform 2 (DDR) or 4 (QDR) operations

    PS..these comments need to be editable!

  4. JFFulcrum

    The story about GDDR clocks is much more complicated. Actually, you have three (!) ‘clocks':

    – Core clock, on which memory chips storage transistors operates.
    – I/O bus clock, on which memory chips buffers/GPU MCU buffers operates, two times more than core clocks.
    – Data transfer rate, two times more than I/O bus clock, thanks for DDR technology.

    The GDDR-5 VRAM is still DDR memory in terms of bus data transfers, not QDR. So, in case of GTX 480:
    924 MHz – core clock
    1848 MHz – I/O bus clock, this one is ‘real’, just as it was in previous generations.
    3696 MHz — effective clock (data transfer rate).

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  7. Athlonite

    I like to use the people in a car on an highway analogy

    single data rate = 1 person in a car driving from home to work

    double data rate = 2 people in a car driving from home to work

    quad data rate = 4 people in a car driving from home to work etc etc …

    and thing of the highway they drive on as the bus that data flows over

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  14. Usman

    Hello everyone! i,ve been reading your articles they are very helpful but i really need your help….This is the first time I am posting on this website….I have Intel core i7 860 2.80Ghz, Intel DP55WG board, 2GB of RAM (kingston), 500GB HDD and a samsung 933bw plus LCD and Nvidia geforce 9600GT 1024MB 256 bits graphics card and a GPU meter installed as a windows gadget but it is not showing any gpu clock 600MHz or memory clock 702 MHz both of them them are showing the usage of 0%…Please Please someone help me out. i really need your help. thanks

  15. bob

    Ok old post but after reading it and seeing every one that posted got it wrong ill just have to set the record straight .

    Sdr 100mgz = 100mgz internal speed~real world speed.

    Ddr~sdr 100mgz internal real speed,100mgz bus speed,200mgz effective speed.

    Ddr2-sdr 100mgz internal real speed,200mgz bus speed,400mgz effective speed.

    Ddr3~sdr 100mgz internal real speed,400mgz bus speed,800mgz effective speed.

    Ddr5~sdr 100mgz internal real speed,400mgz bus speed,1600mgz effective speed.

    And gpu-x reads the external bus speed not the real world internal ram speed.

    To answer the original posters question .

    Gddr5 {notice it called ddr not qdr} 231mgz internal real world speed,924mgz bus speed,3696mgz effective total Public relations QDR bull shit speed number.

    Btw theirs a new standard coming out soon called warp dive effective speed that means x4 more meaning 3696mgz effective qdr = 14786mgz WDqdr.
    Sadly its about as fast as 72pin 10ns edo d-ram but whatever right ? people will buy in to it just wait and see.

    And why do the powers that be do this ?
    Because the marketing Public relations fools just love messing with your heads and lieing about proformance & numbers and we all know bigger numbers sell better …even if its all bull.

    And just look at you all ..you all get it wrong ~ epic fail.

    just look at sdr vs ddr in the first years, ddr1 is 30% faster {bull park number} then sdr not 2x in the real world, real benchmarks.
    Now think about that and think about how fake the effective memory speed really is vs real world speed when it comes to gddr5 errr gqdr5 ram.
    Use to be called ddr5 till someone found a way to blote the numbers
    …enjoy
    ————
    quote
    Then for a GTX 480 (GDDR5) with stock memory speed we have:
    – Real memory speed: 924MHz {wrong bus speed}
    – Effective DDR memory speed: 1848MHz
    – Effective QDR memory speed: 3696MHz

    For a HD 5870 (also GDDR5) we have:
    – Real memory speed: 1200MHz{wrong bus speed}
    – Effective DDR memory speed: 2400MHz
    – Effective QDR memory speed: 4800MHz

    And for a GTX 275 (GDDR3) we have:
    – Real memory speed: 567MHz{wrong bus speed}
    – Effective DDR memory speed: 1134MHz

    ——————–

    as well keep in mind the trick their using to pimp the numbers last i looked in to it is something along the lines of raid0 for hdd only use memory chips to jump bandwidth raid0 ram stile and the real internal speed of the ram is even lower then i stated if you were to put ram speed under a microscope.

  16. bob

    sorry not trying to be a spammer

    btw
    quote
    http://en.wikipedia.org/wiki/GDDR5

    GDDR5 (Graphics Double Data Rate, version 5) SDRAM is a type of high performance DRAM graphics card memory designed for computer applications requiring high bandwidth. Unlike its predecessor, GDDR4, GDDR5 is based on DDR3 SDRAM memory which has double the data lines compared to DDR2 SDRAM, but GDDR5 also has 8-bit wide prefetch buffers similar to GDDR4.

    gddr5 is really ddr3 for the most part and is bubble data rate not QDR

    can you see the lie yet ?

    quote
    http://www.anandtech.com/show/2232/5

    Unbuffered results show the same basic pattern as buffered results in this case. Here DDR3 is clearly the best performer at the same slow timings at DDR2-800, with DDR2 on the P35 behind about 3% and DDR2 on P965 about 12% lower. DDR2 is still faster at the better timings available with current DDR2 memory.

    ddr2 vs ddr3 {gddr5}
    ddr2 is at most 12% slower

    math doesn’t add up douse it on the effective speed improvement …duh…

    ddr2 vs ddr3 effective mgz fake number 400vs800 {x2 100%}

    real world improvement {X 12%}
    —————————–

    http://images.hardwarecanucks.com/image//skymtl/GPU/GTX-550/GTX-550-5.jpg

    now take a look at this pic on the geforce 550ti topic

    gddr5 qdr{lie} effective speed 4100mgz “real world ram speed 256mgz”

    effective memory speed 98.5GB sec

    real world bandwidth
    {-85% fud bull park number}
    98.5gb – 85% PR fud = 14.5GB sec

  17. Jennie

    Unlike its predecessor, GDDR4, GDDR5 is based on DDR3 SDRAM memory which has double the data lines compared to DDR2 SDRAM, but GDDR5 also has 8-bit wide prefetch buffers similar to GDDR4.

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