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Jelle Mees

macrumors newbie
Original poster
Jun 8, 2011
If you don't want to read everything, I marked all the important information in green. So basicly that is all you need to get the final result.

Step 1: Simple overclocking

The ATI Mobility Radeon HD 5750, wich is used in the previous generation iMac ( 2010 ) is not a ATI Mobility Radeon HD 5750 in reality.

Have a look at the official specifications:
Pipelines 400 - unified
Core Speed 550 MHz
Shader Speed 550 MHz
Memory Speed 1600 MHz
Memory Bus Width 128 Bit
Memory Type GDDR5
Max. Amount of Memory 1024 MB

Now let's have a look at the real specifications of the GPU in my iMac:
Pipelines 800 - unified
Core Speed 625 MHz
Shader Speed 625 MHz
Memory Speed 2000 MHz
Memory Bus Width 128 Bit
Memory Type GDDR5
Max. Amount of Memory 1024 MB

For those of you who have doubts, this is what GPU-Z shows:


Now I know what some of you might think. You think that the software misreads the specs of the card. And indeed that's possible.
But wait and read further and I will proove that the specifications are correct.

Now let's search for a mobile GPU with simular official specifications.
You don't have to put to much effort in it, it's the ATI Mobility Radeon HD 5850M.
So the GPU, advertised by Apple as the 5750M is actually the 5850M.
Why? We'll never know. But that's not important. Continue reading...

Now, I don't know if you've taken a look at the official ATI Mobility Radeon HD 5870M, but if not:
Pipelines 800 - unified
Core Speed 700 MHz
Shader Speed 700 MHz
Memory Speed 1000 MHz
Memory Bus Width 128 Bit
Memory Type GDDR5
Max. Amount of Memory 1024 MB

Still with me? The 5870M is nothing more then a slightly higher clocked 5850M. So all that is required is a small, free, tool called "MSI Afterburner" wich you can use to overclock the 5850M ( fake 5750 ) to the 5870M.
It requires no skill, no voltmodding, etc... And it has a usefull option "Apply Overclocking at system startup".

What's so cool about it? Well, since the 6870M is nothing more then an underclocked 5870M ( beleave it or not, the 5870M > 6870M ), you just upgraded your card for free from an ATI 5750M to an ATI 6870M!

That's not all, this GPU can easely get overclocked to 725Mhz/1075Mhz, wich results in a card that performs much better then the ATI 6870M/5870M.

Now, in order to test the actual performance increase, I ran FurMark and 3DMark11 at 2560x1440 to see how much increase it would have on such an high resolution. Gaming on a lower resolution is perfectly possible, but would result in a more blurry view.


In 3DMark11, my score on 2560x1440 went up from 923 to 1033, in other words, the end-result was 11.92% higher.
In Furmark, again on resulution 2560x1440, the score went up from 514 to 583. In other words, 13.42% performance increase.

For those of you who want to know the performance score if you want to compare your system performance:


Step 2: Get rid off the Bootcamp driver, and install the latest one!

Apple and Windows Drivers, it just don't matches. AMD sells many more GPU's thanks to Apple, but when it comes to iMac driver support, it's seems that it's not that important for AMD. You've probably noticed by know that by default, you get the ATI 10.4 driver. When you try to update, the software will search for an update, mention that 11.5 is available, download it and install it. Then, when you go check, it's still the same 10.4 driver. So basicly, iMac users are stuck when it comes to upgrading their driver.

Follow these simple steps:

1. Uninstall the current ATI driver completely and reboot your iMac.
2. Download the following driver and reboot your iMac: 64bit - 32bit

This small driver update from 10.4 to 11.5 will add the following improvements:
- GPU acceleration of H.264 video content using Adobe Flash Player 10.1 ( or higher )
- Video De-blocking support ( Reduces blocking artifacts seen in low-bit rate video during playback )
- Mosquito noise reduction ( Reduces mosquito noise seen in highly compressed progressive video, during playback )
- Official support for OpenGL 4.0 and OpenGL 3.3
- Support for OpenGL 4.1
- OpenGL ES 2.0 support
- Enhanced Pull-down detection ( The Pull-down detection algorithm has been enhanced for higher visual quality on certain types of video content )
- ATI Radeon GPU acceleration of VLC 1.1.1 ( or higher ) Media Player
- Video accleration for HD WMV video content
- Enahnced Dynamic Contrast video controls
- Enhanced Video Quality default options
- Catalyst AI Texture Filtering updates
- Tessellation Controls
- Morphological Anti-Aliasing support
- Stereo 3D gaming support
- Performance increase in 3DMark11/Vantage and many games!
- A lot more Catalyst™ Application Profiles
- Many bugfixes/resolved stability issues and enhancements for Windows 7!
- And a lote more I probably forgot to mention...

Now let's open GPU-Z again:


Well well well... Our ATI Radeon 5750 magicly becomes the "ATI Mobility Radeon HD 5850"!

And for the fun of it, let's run those benchmarks again. In case you have forgotton, the original scores were "923" in 3DMark11, and "514" in Furmark, both tested on resolution 2560x1440.


3DMark11 => 1074! ( = 15,98% increase! )
Furmark => 656! ( = 27.62% increase! )

For those of you who want to know the performance score if you want to compare your system performance:


And offcourse, what's really important is the gaming performance. In UT3 the performance boost wasn't very high, but it's an old game and ATI does not add performance inhancements anymore.



macrumors 6502a
Apr 29, 2004
Auckland, New Zealand
As soon as the 2010 imacs were released, people found this out.

They never advertised it as a '5750M' they advertised it as a '5750'... The 5850M is about the same speed as a desktop 5750.


macrumors newbie
Jul 23, 2012
Actually a little late push but I'm even running it stable at Desktop GFX Speeds right now.

A little fiddle with Afterburner is needed to get it running at first (set overclockmode to 2 instead of 1
to remove any flickering problems occuring due to Powermizer).

800MHZ/1100 MHZ

Together with SMC/Fan Control I set the Fan Speeds to Maximum.

100% GPU Load via Geeks3D FurMark v1.10.6 Burn In Test running over 15 Minutes now it has a Max Temp of 61 °C (Test still running). Seeing that those Cards are usually running at 70-80 °C while under idle in Stock Notebook Systems I believe even higher Speeds are possible.

Results are around 25-30% more FPS in Battlefield 3 Multiplayer (45 Min, 50 AVG, 71 MAX).
All Settings HIGH, 1920x1080p Resolution. Yes I know that that isn't the native Resolution but I believe the VRAM/CPU Combination (i5 2.8GHZ) isn't strong enought to handle it stable that 's why I get a constant 30 FPS no matter how much I overclock my card or what Settings I set.

That 's why I'm getting an external 23 ' Monitor to play it at 1080p withouth any scaling. But that 's OT ... oh well ...


Idle Temp 46 °C

Edit 2:

FurMark seems not to run well (in terms of FPS not stability) thats why I searched and
found a better Testing Tool MSI Kombustor 2.5.2

GF OC Test:

Stock - 45 FPS AVG - Didn't messure Temp
800/1100 - 55 FPS AVG (22% Increase) - 50 °C
820/1150 - 60 FPS AVG (33% Increase) - 51 °C

Ah and Tempratures are taken from GPU-Z/HWiNFO32 as the testing tools fail to get the sensor data somehow. :)
Last edited:


macrumors newbie
Oct 18, 2014
maverics and 6870m

I had the impression that with maverics the 6870 card should work without separate download of drivers. Encouraged by this information about clocking 5000 series, I ordered a used 6870m card, which is supposed to be from alienware laptop.All, I get is black screen though. Starting up in safe mode and zapping P(V)RAM did not help and that's about all I can think of doing to fix it. I checked all the connections and nothing obvious seems to be wrong inside. I want to find out if this is more likely to be a problem with the drivers or if my card is just disfunctional.
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