Radeon HD 4870 CrossFire: The Benefit Of CPU Overclocking
In some games, a CPU at its default clock speed is not able to realize the full potential of a Radeon HD 4870. Running two graphics cards in CrossFire mode amplifies this issue, making overclocking particularly attractive for anyone with a high-end array of 4870s.
| Assassins Creed in fps | 12800xAA | 16800xAA | 19200xAA | 12804xAA | 16804xAA | 19204xAA | Overall |
|---|---|---|---|---|---|---|---|
| HD 4870 CF (512 MB) 8.8 | 55.4 | 55.9 | 56.7 | 42.6 | 42.1 | 42.9 | 295.6 |
| HD 4870 CF (512 MB) CPU@3.47 | 64.0 | 64.6 | 64.8 | 49.5 | 48.6 | 48.8 | 340.3 |
| Difference in performance in percentage | 15.5 | 15.6 | 14.3 | 16.2 | 15.4 | 13.8 | 15.1 |
The 18.2 percent additional CPU clock rate is converted by the CrossFire combination to 15 percent higher frame rates. The big performance boost makes us want a 4GHz CPU to better show off the pair’s potential.
| Call of Duty 4 in fps | 12800xAA | 16800xAA | 19200xAA | 12804xAA | 16804xAA | 19204xAA | Overall |
|---|---|---|---|---|---|---|---|
| HD 4870 CF (512 MB) 8.8 | 147.5 | 140.0 | 129.6 | 135.4 | 116.8 | 107.3 | 776.6 |
| HD 4870 CF (512 MB) CPU@3.47 | 154.1 | 148.6 | 136.1 | 138.4 | 123.4 | 113.7 | 814.3 |
| Difference in performance in percentage | 4.5 | 6.1 | 5.0 | 2.2 | 5.7 | 6.0 | 4.9 |
Call of Duty 4 shows a 5 percent overall performance improvement.
| Crysis High in fps | 12800xAA | 16800xAA | 19200xAA | 12804xAA | 16804xAA | 19204xAA | Overall |
|---|---|---|---|---|---|---|---|
| HD 4870 CF (512 MB) 8.8 | 29.3 | 25.8 | 26.7 | 24.2 | 21.3 | 20.4 | 147.7 |
| HD 4870 CF (512 MB) CPU@3.47 | 32.1 | 30.6 | 30.1 | 27.0 | 24.3 | 23.7 | 167.8 |
| Difference in performance in percentage | 9.6 | 18.6 | 12.7 | 11.6 | 14.1 | 16.2 | 13.6 |
Crysis gains a lot; even the overclocked CPU is not sufficient to fully tax the CrossFire combination. Here, the graphics card clearly has higher available performance just waiting to be used by an even more powerful processor.
| Crysis Very High in fps | 12800xAA | 16800xAA | 19200xAA | 12804xAA | 16804xAA | 19204xAA | Overall |
|---|---|---|---|---|---|---|---|
| HD 4870 CF (512 MB) 8.8 | 26.7 | 24.8 | 20.9 | 22.0 | 18.0 | 12.9 | 125.3 |
| HD 4870 CF (512 MB) CPU@3.47 | 30.4 | 27.9 | 25.7 | 24.7 | 20.8 | 13.2 | 142.7 |
| Difference in performance in percentage | 13.9 | 12.5 | 23.0 | 12.3 | 15.6 | 2.3 | 13.9 |
The increased performance attributable to the higher CPU clock rate is readily taken advantage of, yet only when we get to 1920x1200 pixels with anti-aliasing enabled do we get close to the combo’s limit.
| ET: Quake Wars in fps | 12800xAA | 16800xAA | 19200xAA | 12804xAA | 16804xAA | 19204xAA | Overall |
|---|---|---|---|---|---|---|---|
| HD 4870 CF (512 MB) 8.7 | 65.0 | 65.6 | 65.2 | 62.6 | 62.7 | 62.5 | 383.6 |
| HD 4870 CF (512 MB) CPU@3.47 | 75.7 | 74.9 | 74.1 | 70.4 | 70.0 | 70.0 | 435.1 |
| Difference in performance in percentage | 16.5 | 14.2 | 13.7 | 12.5 | 11.6 | 12.0 | 13.4 |
Again, with the Catalyst 8.8 the game does not start, so the test values were measured using the Catalyst 8.7 graphics driver. In Quake Wars, the additional 18.2 percent CPU clock rate results in significantly better frame rates. In CrossFire mode, the cards don’t even get close to their limit. A much more powerful CPU would use the duo more effectively.
| Half-Life 2 Episode 2 in fps | 12800xAA | 16800xAA | 19200xAA | 12804xAA | 16804xAA | 19204xAA | Overall |
|---|---|---|---|---|---|---|---|
| HD 4870 CF (512 MB) 8.8 | 104.7 | 99.5 | 98.3 | 102.5 | 99.0 | 97.1 | 601.1 |
| HD 4870 CF (512 MB) CPU@3.47 | 115.3 | 109.3 | 107.8 | 112.7 | 108.7 | 107.6 | 661.4 |
| Difference in performance in percentage | 10.1 | 9.8 | 9.7 | 10.0 | 9.8 | 10.8 | 10.0 |
Half-Life 2 Episode 2 shows 10 percent higher frame rates in all test resolutions. CrossFire clearly has greater potential, and a more powerful CPU will be able to unleash additional power.
| Mass Effect in fps | 12800xAA | 16800xAA | 19200xAA | 12804xAA | 16804xAA | 19204xAA | 12808xAA | 16808xAA | 19208xAA | Overall |
|---|---|---|---|---|---|---|---|---|---|---|
| HD 4870 CF (512 MB) 8.8 | 92.6 | 91.7 | 89.3 | 87.3 | 86.2 | 74.7 | 88.0 | 84.0 | 72.7 | 766.5 |
| HD 4870 CF (512 MB) CPU@3.47 | 98.7 | 96.2 | 93.5 | 94.9 | 90.9 | 75.8 | 93.8 | 89.8 | 73.7 | 807.3 |
| Difference in performance in percentage | 6.6 | 4.9 | 4.7 | 8.7 | 5.5 | 1.5 | 6.6 | 6.9 | 1.4 | 5.3 |
A minor increase could be measured, but in the 1920 resolution with anti-aliasing (4xAA and 8xAA) the cards approach their limits.
| MS Flight Simulator X SP2 in fps | 12800xAA | 16800xAA | 19200xAA | 12804xAA | 16804xAA | 19204xAA | Overall |
|---|---|---|---|---|---|---|---|
| HD 4870 CF (512 MB) 8.8 | 24.5 | 24.9 | 24.4 | 24.6 | 25.0 | 24.7 | 148.1 |
| HD 4870 CF (512 MB) CPU@3.47 | 27.4 | 28.1 | 28.4 | 27.9 | 28.7 | 28.9 | 169.4 |
| Difference in performance in percentage | 11.8 | 12.9 | 16.4 | 13.4 | 14.8 | 17.0 | 14.4 |
The flight simulator also gains from the overclocking processor to the tune of double digits. In CrossFire, the Radeon HD 4870 offers greater power when the duo is supplied with a more powerful CPU.
| World in Conflict in fps | 12800xAA | 16800xAA | 19200xAA | 12804xAA | 16804xAA | 19204xAA | Overall |
|---|---|---|---|---|---|---|---|
| HD 4870 CF (512 MB) 8.8 | 46.0 | 46.9 | 45.6 | 43.4 | 46.0 | 43.2 | 271.1 |
| HD 4870 CF (512 MB) CPU@3.47 | 49.4 | 52.5 | 50.1 | 46.8 | 52.0 | 50.6 | 301.4 |
| Difference in performance in percentage | 7.4 | 11.9 | 9.9 | 7.8 | 13.0 | 17.1 | 11.2 |
With anti-aliasing, the CrossFire combination is even faster; the additional 18.2 percent CPU clock rate is converted by the graphics cards into 17.1 percent higher frame rates. Here, again, there’s still a lot of potential available to the dual-card setup, and a higher-clocked CPU would almost certainly provide additional 3D performance.