ATI changed the way clocks are determined with the X1800 XT. It now has a 2D and 3D clock. It’s not exactly the same as Nvidia’s approach and makes overclocking quite a messy business. With a little information however, it can be rectified.

The problem is that there is no overclocking tool available that allows reliable tweaking of the 2D and 3D clocks. Let’s take ATI tool as an example. The clocks you will see and be able to weak in ATI Tool are the 2D clocks. Sure, you can play about with those and find what clocks your card can do, but as soon as you jump in a full screen 3D game it will not be reading the 2D clocks anymore, it will use the 3D clocks. As you may have guessed, you didn’t touch the 3D clocks and so once in game you’ll be running at 625/750.

The way round this is quite simple. First you must disable two ATI services called ATI Smart and ATI Hotkey. To do this you need to goto:

• Start / Run – type in “msconfig” and click OK 
• Click the tab “Services”
• Disable ATI Hotkey Poller and ATI Smart
• Click OK and restart system.

On disabling these services you loose Overdrive in the CCC but you can still monitor temperatures using ATI Tool. Another side effect is that VPU Recover doesn’t…. recover, so if you push your clocks too far don’t expect your card to reset and then jump back into Windows, it will most likely hang indefinitely.

What you have effectively done is disable the 3D clock from being used. Now the clocks you see in ATI tool are the ones used for all applications so you can raise the clocks, test them using the Artifact scanner and then jump in 3D Mark or a game safe in the knowledge that the card is running at the clocks you set. 

With that out of the way let’s get back to this cards results. I mentioned earlier that you can tweak the voltages of your card to achieve much higher overclocks than you would normally expect. The results below were achieved at stock with no voltage increase. This means I used 1.275v for the core, 2.1v for MVDDC, and the same for MVDDQ. It keeps things fair and honest if I declare this. All our video card reviews are run with default voltages unless stated otherwise.

I recommend you get a better cooler if you want to increase the voltages, but I’ll tell you right now that raising the core to 1.3v will net you quite a lot, probably an extra 30 MHz.

The Sapphire’s core runs at the same frequency as ATI’s reference card. Only X1800XT PE cards come factory overclocked. I was able to reach 677 MHz on the core with absolute stability. As already mentioned, if you play with the volts it will go substantially higher than this.

Moving on to memory I was able to clock to 841 MHz, and 91 MHz increase. This is quite a jump, and once again this is with default volts so you can imagine how high it would go with a little extra juice.