ATI Radeon X1900 XTX And CrossFire: R580 Is Here
Overclocking the Radeon X1900
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For our next set of performance metrics, we spent a little time overclocking the Radeon X1900 XTX and the XTX / X1900 CrossFire Combo using the clock frequency slider available within ATI's drivers, under the "Overdrive" tab.
We'd like to note that overclocking video cards in a dual-GPU configuration is somewhat more difficult than overclocking a single card. When overclocking a pair of cards, your peak overclock will be limited by whichever card overclocks the lowest. If card A's core can hit 700MHz, and card B's core can hit 690MHz, both cards end up being clocked at 690MHz, even though card B still has some clock speed headroom to spare. Each card is not currently overclocked individually, although this may change in future driver releases.
CrossFire Overclocked Speeds: 631MHz Core / 797MHz (1.59GHz DDR) Memory
X1900 XTX Overclocked Speeds: 689MHz Core / 797MHz (1.59GHz DDR) Memory
CrossFire Overclocked Speeds: 631MHz Core / 797MHz (1.59GHz DDR) Memory
X1900 XTX Overclocked Speeds: 689MHz Core / 797MHz (1.59GHz DDR) Memory
We had limited success while overclocking in CrossFire mode, but had much better luck with the single Radeon X1900 XTX. In CrossFire mode, we were only able to increase the Master card's core clock speed to 631MHz, up from 625MHz. The memory, however, was much more cooperative and peaked at 797MHz (1.59GHz DDR). By itself, the Radeon X1900 XTX hit a peak core clock speed of 689MHz, with the same 797MHz memory speed. It seems there is a bit of clock speed headroom left in the X1900 considering we squeezed and additional 39MHz out of the core, so we suspect with more updated overclocking tools, cranking up core clock speeds in CrossFire mode will be possible.
While overclocked, we re-ran a couple of benchmarks to see what kind of additional performance we gained by raising the cards' core and memory clock speeds. In a single-card configuration, the Radeon X1900 XTX's 3DMark06 score jumped by 175 points, and its frame rate in our high-resolution Doom 3 benchmark went up by 3.2 FPS. In CrossFire mode, we saw somewhat smaller gains though. With the pair of X1900s overclocked, the 3DMark06 score increased by less than 100 points, and Doom 3's frame rate went up by only 2.8 frames per second.
