Sapphire Radeon HD2900XT

It's been a long time coming, but the new DirectX 10 capable Radeon from ATI has finally arrived. Outside the reference board ATI gave us to play with, the Sapphire Radeon HD 2900 XT is our first look at this product and all its new features.

Although NVIDIA hit the market considerably earlier with its G80 GPU (graphics processing unit), and even managed to get a mid-range line-up out before ATI released its first DirectX 10 card, the reality is that no DirectX 10 games have been released yet, so what's the rush?

Like the competing NVIDIA GPU, the ATI Radeon GPU (codenamed R600) used in this Sapphire HD 2900 XT has not only moved to DirectX 10, but has made the switch to a more efficient unified shader architecture. However, it doesn't stop there. The HD 2900 XT offers a dedicated video decoder, native Crossfire support (eliminating the need for a special 'master' card), adaptive custom filter anti-aliasing (CFAA) and also boasts the first true 512-bit memory bus. Our Sapphire card has 512MB of GDDR3 memory, but we expect to see DDR4 version of these cards soon. The core clock speed runs at a whopping 740MHz while the memory runs at a less dizzying 1650MHz.

The new generation GPU uses dynamic stream processors, rather than the fixed pixel and vertex shaders from ATI's X1900 series. The stream processors can do pixel shading, vertex shading, physics processing and the new geometry shading introduced by DirectX 10. Geometry shaders add a few nice features. Put simply they allow tasks that would otherwise have been too taxing on the GPU in DirectX 9, or do them faster and more efficiently. For instance, rendering a scene with dynamic lighting from multiple light sources can be a processing costly task, but with geometry shaders and DirectX 10 it's possible to cut back on the amount data that needs to be handled. This either leads to faster frames or more complex scenes, both of which are a plus.

Geometry shaders also allow a process called tessellation, which takes existing triangles (which make up a scene) and breaks them up into smaller triangles to allow smoother more rounded and detailed objects. As well as having the geometry shaders like those found in NVIDIA's cards the HD 2900 XT also has a programmable tessellation unit based on the same technology used in the Xbox 360. However, the tessellation unit is not part of the DirectX 10 specification, so it's not certain how much use it will get. Its similarity to the Xenos GPU in the Xbox 360 means it may get some attention from developers, and it may feature more in later updates of DirectX, but we're yet to see this.

Another improvement from its last generation of cards, the Sapphire HD 2900 XT also has native Crossfire support. This simply means that you'll no longer need a special master card to set two cards up in a Crossfire dual-card configuration. The new Crossfire support also claims greater efficiency, moving the twin card setup closer to the theoretical maximum of twice the performance. We are yet to run Crossfire tests to confirm this.

Among a few new anti-aliasing (AA) improvements found in this card, including up to 8x multi-sample anti-aliasing (MSAA), the most interesting is called custom filter anti-aliasing (CFAA). Standard AA smooths out edges and 'jaggies' by blending multiple sub-pixels samples into one by using a fixed weight. The process is effective, but can distort the image quality by blending some sub-pixels unnecessarily. CFAA also aims to take objects that appear blocky or jagged and smooth them out. However, CFAA uses an adaptable weighting system that allows sampling from sub-pixels to be done dynamically, reducing the loss of image quality. The programmable nature of CFAA also allows ATI to update the functions ability through driver changes over time, a beaut feature.

The HD 2900 XT also implements ATI's latest progression of the ring-bus memory controller design. It's also the first card to use a true 512-bit memory bus, which improves the bandwidth throughput potential using existing tried and tested memory technology.

As well as all the performance tweaks the Sapphire HD 2900 XT also includes an HDMI/DVI adapter and supports HDMI output for both video and audio. Like the NVIDIA 8600 and 8500 cards all the new ATI Radeon cards will have a dedicated video decoder called UVD, which does the job of decoding video that was formerly handled by the CPU and has been designed to handle high-definition formats such as Blu-ray and HD-DVD movies. Naturally, with all this high-definition support the card has also been made HDCP compliant.

Although the new performance features are great when using DirectX 9 based tests, the true test is going to be in DirectX 10 applications. We attempted to run the Sapphire HD 2900 XT through some DirectX 10 games (Call of Juarez and Lost Planet) but ran into problems either starting the games or rendering problems during the benchmarks, so results could not be obtained at the time. However, we also put it through our old DirectX 9 tests.

In 3DMark 2006 at the default settings (1280x1024 no AA and no anisotropic filtering), the Sapphire HD 2900 XT scored 11192, and beat the EN8800GTS 640, which scored 9309, but it is not quite as speedy as the NX8800GTX-T2D768E-HD, which scored 11894. At 1920x1200, with 8xAA and 16xAF it scored 4493, quite fast for such a high resolution and good enough to run current games easily.

In F.E.A.R at 1280x960 using 4xAA and 16xAF it averaged 88fps (frames per second), while at 1600x1200 using the same quality settings it scored an average of 63fps, both very playable frame rates. With the price in mind these scores are more than a little competition for NVIDIA's 8800 series.

The Sapphire Radeon HD 2900 XT requires two 6-pin PCI Express power cables to be plugged in, one of which can be replaced by an 8-pin power cable for overclocking. Adding to the value of this card is a voucher for Valve's Half Life 2, Half Life 2 Episode 2, Team Fortress 2 and Portal games when they are eventually released.