AMD Radeon HD 6990 4GB Review

Overclocking Results

In their marketing documents, AMD states that the HD 6990 is geared towards enthusiasts since it offers a wealth of overclocking options. Through the use of the dual BIOS switch on the card (otherwise known as the hopelessly named Antilles Unlocking Switch for Uber Mode), enthusiasts can change between a default profile and a more aggressive setup which pushes additional voltage towards the core and ups the GPU’s clock to 880Mhz.

We used both positions in our overclocking along with boosting PowerTune’s overhead to +20% but all in all, the results were a bit mixed since the core did overclock reasonably well but the memory on our card seemed to be held back. Also remember that a “stable” overclock for us means the ability to complete a 1 hour loop of Unigine: Heaven without any artifacts or crashes..

Default BIOS Overclocking (Position 2)

Max Stable Core Clock: 870Mhz
Max Stable Memory Clock: 5444Mhz


“Performance” Profile Overclocking (Position 1)

Max Stable Core Clock: 972Mhz
Max Stable Memory Clock: 5444Mhz

Touching Upon Overclocked Performance

There are two things to be learned from these results: pushing clock speeds on the HD 6990 can pay dividends but using the BIOS switch is absolutely pointless if you aren’t planning to overclock.

At 972Mhz, the cores are able to work in tandem to spit out some downright incredible framerates and yet there is a heavy price to pay…

Power Consumption

The words “mind blowing” come to mind when looking at these results. With the BIOS switch in Position 1 and additional voltage coursing through the cores, we can definitely see where the 450W claim comes from. In addition, just moving the switch without actively increasing the clocks past 880Mhz still results in much higher power requirements since the cores are being fed with higher voltages.

With all of this in mind, several questions must be raised before proceeding to overclock this card. More overclocking will cause massive amounts power to be pulled from the PCI-E slot so buying a motherboard with an optional GPU Molex or FDD power connector would be a good idea. This will feed more +12V power to the GPU.

In addition, anything more than 400W of draw could spell trouble for some multi rail power supplies with 18A rails. For these cases, we recommend that you be very careful with which connectors are used for the HD 6990.