Overclocking The Radeon HD 2900 XT
For our next set of performance metrics, we spent some time overclocking the Radeon HD 2900 XT using the clock frequency sliders available within ATI's Catalyst drivers, under the "Overdrive" menu.
Please note, that overclocking is NOT supported in the Radeon HD 2900 XT with the Catalyst drivers unless an 8-Pin PCI Express supplemental power connector is plugged into the card, along with a secondary 6-Pin feed. When asked why they made the 8-Pin connector a requirement for overclocking, representative from ATI said it was due to major variations in power consumption between not only between stock and overclocked configurations, but between different HD 2900 XT GPUs. It seems TSMC's 80nm HS process allowed ATI to clock the R600 relatively high, but once the upper limits of the GPU's clock speed are hit, power consumption can vary considerable from card to card. Having the 8-Pin supplemental feed available means there should always be ample power available to the card.
With this in mind, we monitored power consumption throughout our overclocking experiments and didn't witness any major changes in consumption at all, despite running the memory and GPU at frequencies 100MHz and 85MHz higher than stock. More on power consumption on the next page...
To find the Radeon HD 2900 XT's peak core and memory frequencies, we slowly raised their respective sliders until we begun to see visual artifacts on-screen while running a game or benchmark, or until our test system was no longer stable. Because the Overdrive tab only allowed for a peak memory frequency of 900MHz, we were able to max that one out. The GPU peaked at 828MHz - a healthy increase of 85MHz.
While we had the card overclocked, we re-ran the F.E.A.R. and S.T.A.L.K.E.R. benchmark at 1600x1200 to see just how much performance had increased. As you can see, the HD 2900 XT's performance in the F.E.A.R. test jumped by 4 frames per second, or roughly 6.4%. And in S.T.A.L.K.E.R. its performance went up by a little over 3 frames per second, or about 8.1%.