Review: Sapphire Radeon HD4870 X2 graphics card

ATI has once again turned its attention to regaining the top spot in the performance stakes – something it relinquished to Nvidia many moons ago. The tool it has chosen to get back the title is the R700 core, or to give its stage name, the HD4870 X2.

The clue to what the HD4870 X2 is all about is in the X2 part of the name. A single RV770 (HD4870) core was fast, so having two on a single card means a huge amount of performance. It follows on from the previous generation’s HD3870 X2 and looks very much like it in appearance, but under the skin it’s a different ball game altogether.

ATI has used a second generation x16 PCI Express 2.0 switch rather than the 1.1 found on the HD3870 X2, giving the HD4870 X2 a huge communication channel of some 5GB/sec bi-directional, which allows fast data transfers between each core – just what you need for rendering modern games.

The HD4870 X2 also supports Sideport (ATI’s dedicated display cache), but because no software can currently use it, it has been disabled. When enabled, it will give the cores an additional 5GB/sec of bandwidth in each direction, which should give the HD4870 X2 some 21.8GB/sec of internal bandwidth.

Each core is clocked at 750MHz, as are the 800 shaders, while the GDDR5 memory is clocked at 3.6GHz. Because dual GPU cards cannot share the frame buffer, each RV770 core comes with its own 1GB of memory. Although the memory runs through a mere 256-bit memory bus, the sheer speed of GDDR5 makes up for the small size.

Sticking to the reference design, Sapphire’s board has one of its attractive Lara Croft clone stickers on the cooler to separate it from the rest.