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HD4850 incorrect memory clock

Discussion in 'GPU-Z' started by aquax, Aug 11, 2008.

  1. aquax New Member

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    Why GPU-Z under load read my memory clock 975MHz instead of 993?

    CCC reads it 993

    [​IMG]
     
  2. W1zzard

    W1zzard Administrator Staff Member

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    second tab of gpuz reads the clocks directly from the pll. the first tab shows the requested clocks for 3d, based on all info i've seen so far, the numbers on tab 2 are as accurate as they get
     
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  3. aquax New Member

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    I always see it 975MHz under heavy 3d so that's mean the memory is really running at 975MHz?
     
  4. alexp999

    alexp999 Staff

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    Probably. Its like the HIS 3870 Turbo I had. It was sold as 850 Core, but due to the way internal clock frequencies are set it actually ran at 837Mhz. And GPU-Z shows the true clock frequency.
     
  5. XSAlliN

    XSAlliN

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    1950 - effectively, yet all reference cards should have 993 Mhz yous has 975 Mhz, so It's downclock a little. Sue them... :)
     
  6. sleepsus New Member

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    I have a similar experience with GPU-Z.

    On my Palit HD3850 I did a bios edit of the clock speeds and set it as 823/908.

    GPU-Z (and Everest) reads the clocks as 810/900

    BUT

    AMD Overdrive reads the clocks at a closer value to what I set in bios - 822.69/907.17

    So now I'm confused as to which of the two is reporting the actual and effective clocks?

    http://forums.techpowerup.com/showthread.php?t=68249
     
  7. nafets New Member

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    I questioned W1zzard about the very same problem, regarding the memory clocks, and what Gpu-Z reports. Here's what I remember (my terminology may not be totally correct):

    Basically the PLL on the ATI cards only reports memory clocks in 25MHz steps.

    So your actual value will be reported in Gpu-Z at a value rounded down to the nearest 25MHz step.

    Examples:

    492MHz MEM shows up as 475MHz
    456MHz MEM shows up as 450MHz
    445MHz MEM shows up as 425MHz
    418MHz MEM shows up as 400MHz

    If you want the true MEMORY clock value of your card at it's current state (2D/3DLP/3DHP), download and run AMD Gpu Clock Tool v0.9.8. Click on the "Get Clock Settings" button and it will display your current GPU/MEMORY clocks down the to nearest hundredth of a MHz...
     
  8. W1zzard

    W1zzard Administrator Staff Member

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    i dont think the problem is reporting but actual speed.

    try benchmarking your card at the lower end of a 25 mhz step and at the upper end of a 25 mhz step.

    for example 400.1 and 424.9 so that gpuz shows the same clock in sensors every time. now if you consistenly get higher scores at 424.9 i will look into gpuz clock readings
     
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  9. nafets New Member

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    Ok, let's see something. Using AMD Gpu Clock Tool to set memory clocks, for all tests.

    Using AMD Gpu Clock Tool to check clocks.

    Memory set at = Reports at
    399.9MHz = 396.87MHz
    400.1MHz = 400MHz
    401MHz = 400MHz
    402MHz = 400MHz
    403MHz = 400MHz
    404MHz = 403.12MHz

    421MHz = 418.75MHz
    422MHz = 421.87MHz
    423MHz = 421.87MHz
    424MHz = 421.87MHz
    424.9MHz = 421.87MHz
    425.1MHz = 425MHz

    AMD GPU Clock Tool reports memory clocks in 3.12(5)MHz steppings. So you can throw out my previous statement on it's accuracy.

    ------------------------------------

    Using Gpu-Z Graphics Card Tab to check clocks (Memory clock listed right under the Driver Version)

    Memory set at = Reports at
    399.9MHz = 399MHz
    400.1MHz = 400MHz
    401MHz = 401MHz
    402MHz = 402MHz
    403MHz = 403MHz
    404MHz = 404MHz

    421MHz = 421MHz
    422MHz = 422MHz
    423MHz = 423MHz
    424MHz = 424MHz
    424.9MHz = 424MHz
    425.1MHz = 425MHz

    Gpu-Z Graphics Card Tab reports the locked/3D Memory clock to the nearest MHz. Great

    ------------------------------------

    Using Gpu-Z Sensors Tab to check clocks (GPU Memory Clock)

    Memory set at = Reports at
    399.9MHz = 375MHz
    400.1MHz = 400MHz
    401MHz = 400MHz
    402MHz = 400MHz
    403MHz = 400MHz
    404MHz = 400MHz

    421MHz = 400MHz
    422MHz = 400MHz
    423MHz = 400MHz
    424MHz = 400MHz
    424.9MHz = 400MHz
    425.1MHz = 425MHz

    Gpu-Z Sensors Tab reports memory clocks in 25Mhz steppings.

    ------------------------------------

    Benchmarking with Furmark

    750/400.1 - 1545 o3Marks
    750/424.9 - 1641 o3Marks (+6.2% increase over 400.1)
    750/425.1 - 1654 o3Marks (+0.8% increase over 424.9)

    What can we conclude from this?

    1. Gpu-Z Sensors Tab is obviously reporting incorrectly.
    2. Maximum margin of difference between actual and reported memory clocks is around 3MHz.
    3. I am probably wrong about something and/or my methods are horribly mistaken.

    Chime in if you got any other ideas...
     
  10. aquax New Member

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    I checked my own bios and memory clocks is set to 993MHz so I don't think it is downclock.
    I also found a review for the HD 4850 and I saw same memory clock reported in the review 975MHz instead of 993MHz, I think GPU-Z just can't read 993MHz.

    Well, I overclocked the memory to 1000MHz and now GPU-Z Report 1000MHz
     
  11. nafets New Member

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    If you keep the memory clock at a 25MHz stepping (like 1000MHz), you don't have to worry whether or not it's actually running at that speed. It's pretty much guaranteed... :)
     

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