[Tutorial] 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
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 shows real memory speed
EVGA Precision shows DDR memory speed
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
Related posts:
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!)
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
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!
[...] GPU: GF104 @ 675MHz – Shader processors: 336 @ 1350MHz – Memory: 768MB GDDR5 @ 1800MHz DDR speed – TDP: [...]
[...] are the clocks of this GTX 470: – GPU: 630MHz (ref=607MHz) – Shader: 1260MHz (ref=1215MHz) – Memory speed: 850MHz real speed or 1700 DDR speed. Ref=837MHz real [...]
[...] and Direct3D 11). The HD5670 ULTIMATE comes with reference clocks: GPU=775MHz and memory=4000MHz QDR speed and is priced at around 110 euros. Nice VGA cooler, I like [...]
[...] Memory: 768MB (192-bit) or 1024MB (256-bit) GDDR5 @ 900MHz (real speed) or 1800MHz (DDR speed) or 3600MHz (QDR speed). More information about graphics memory speed HERE. [...]
[...] 43°C for a GTX 480 stressed by FurMark is an impressive GPU temperature! Especially for an overclocked GTX 480: the GPU is factory-clocked at 752MHz (reference = 700MHz, see HERE) as well as the memory with around 100Mhz in more: 3800MHz QDR speed. [...]
[...] 2.5GB GDDR5 @ 750MHz real speed (or 3000MHz QDR speed) with ECC / [...]
[...] GTX 460 – GPU: 675MHz, mem: 900MHz real speed. [...]
[...] is writting on Asus EN GTS 450 TOP box). – CUDA cores: 192 @ 1566MHz – Memory: 1GB GDDR5 @ 3608MHz QDR speed or 902MHz real speed, 128-bit – Power connector: one 6-pin – 3D APIs: OpenGL 4.1 and Direct3D 11 – [...]
[...] 2GB DDR3 128-bit @ 1800MHz DDR speed or 900MHz real speed (the one displayed by [...]
[...] KFA2 has announced a SLI pack that includes two GTX 460. Each GeForce GTX 460 comes with a little overclocking: 700MHz for the GPU. The memory keeps the stock clock with 1848MHz DDR speed. [...]