# HD4850 incorrect memory clock



## aquax (Aug 11, 2008)

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

CCC reads it 993


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## W1zzard (Aug 11, 2008)

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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## aquax (Aug 11, 2008)

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


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## alexp999 (Aug 11, 2008)

aquax said:


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



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.


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## XSAlliN (Aug 13, 2008)

aquax said:


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



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


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## sleepsus (Aug 13, 2008)

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


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## nafets (Aug 13, 2008)

W1zzard said:


> 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



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...


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## W1zzard (Aug 13, 2008)

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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## nafets (Aug 13, 2008)

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...


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## aquax (Aug 13, 2008)

XSAlliN said:


> 1950 - effectively, yet all reference cards should have 993 Mhz yous has 975 Mhz, so It's downclock a little. Sue them...



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


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## nafets (Aug 14, 2008)

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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