Radeon HD 4870 X2 Specifications and Ports
Up until recently, dual-chip cards have suffered several disadvantages. An important one was that the GPU and memory speeds had to be lowered to compensate for the thermal and electrical demands of doubling up on one card’s attributes. Naturally, performance would drop as a result, making two single cards in CrossFire mode faster. Driver optimizations also usually took longer; the HD 3870 X2 had a long lead time before we could actually see optimized results.
The biggest advantage of double-chip cards, though, is that you only need one PCIe slot, giving you more options to choose from when it comes to picking a favorite motherboard.
AMD has made several improvements with its Radeon HD 4870 X2, making the current X2 card more attractive than its predecessors. It supports PowerPlay for lower power consumption, which is still missing for the single-chip HD 4870 with Catalyst 8.10 (it consumes 20 watts more per graphics chip in 2D mode). The X2 also boasts the single card’s full clock rate of 750 MHz and memory running at 900 MHz (or GDDR5 clock speed 3600 MHz), full 2x1024 MB graphics memory, and a fan that isn’t louder than two single cards. However, the noise level can vary if the fan profile is changed (like with the MSI OC edition).
AMD’s Radeon 4870 supports DirectX 10.1 with Shader 4.1, and can provide 8 channel audio to the HDMI port. There is no need for internal wiring; you only need a DVI HDMI adapter, which was shipped with all of the test cards. There are two DVI ports and one component video output, too.
Power comes from 6-pin and 8-pin plugs. The test system with its overclocked quad-core CPU consumes 480 watts from the socket. For the power supply, this means a load of 408 watts and 34 amps at 12 V. In 2D mode, the clock speed is lowered to 507 MHz GPU and 500 MHz memory, causing the power consumption to drop down to 202 watts (as long as you don’t get stuck with 240 watts after Vista restart because of the driver error). By contrast, the single-chip Radeon HD 4870 does not lower the clock speed with Catalyst 8.10, consuming 280 watts when two cards are combined in CrossFire mode.
To drive the dual-chip card properly, you really need a good, fast CPU. There is a 21.2% difference in overall performance between the standard CPU X6800 Extreme Edition at 2.93 GHz and an overclocked quad-core CPU QX6850 at 3.67 GHz. Of course, you can also combine two Radeon HD 4870 X2 via CrossFire (4CF), combining the cooperative efforts of four graphics chips. But the gain in overall performance is rather low here because the CPU limits the capabilities of this arrangement. For more information on how the various platforms scale with increased graphics horsepower, check out Core i7: 4-Way CrossFire, 3-way SLI, Paradise?