SiS Xabre400 review

If you're after a new graphics card, there's certainly no shortage of boards on the market, as last month's graphics card group test illustrated (see Labs, issue 93, p74). However, if you take a closer look, you'll notice that almost every model uses chipsets from Nvidia or ATi. Since the demise of 3dfx and the absence in recent years of other players such as S3 and Matrox from the 3D arena, it's become very much a two-horse race.

However, this is set to change in the near future, with strong challenges appearing from Matrox with its Parhelia-512 and new chipsets from 3Dlabs under the Creative brand. But while the cards from Matrox and 3Dlabs look likely to enter at the high end of the market, an unlikely challenger has taken up the gauntlet at the low end. The Xabre400 is a brand-new chipset from prominent Taiwanese chipset manufacturer SiS. It offers the latest DirectX 8 Pixel Shaders, but costs less than a GeForce4 MX 440.

While SiS isn't new to the graphics card sector, it hasn't previously attempted to produce a premium product with advanced 3D features. The SiS315 chipset was its most recent, offering a GeForce2 MX-type feature set, although it wasn't widely available and was dated compared to the best cards at the time.

For the Xabre400, it's obvious that SiS has examined the competition in great detail and incorporated a large number of features offered by the current high-end boards.

The initial specification certainly looks impressive, with a 250MHz core clock coupled with 64Mb of 250MHz DDR memory (effectively 500MHz). However, the most significant feature is what SiS is calling the Pixelizer Engine, referring to hardware Pixel Shader support.

The Xabre400 has version 1.3 Pixel Shaders, comparable to those found in the GeForce3 and GeForce4 Ti chipsets from Nvidia. This means that, unlike similarly priced DirectX 7-based chipsets - such as the GeForce4 MX - the Xabre400 is capable of the advanced visual effects appearing in the latest games.

However, while Pixel Shader support is a key feature, the Xabre400 differs from all the other current DirectX 8 cards in that it only has a fixed function Transformation and Lighting (T&L) engine and no Vertex Shaders. As Vertex Shaders provide the specialised animation effects, this may seem like a major omission. But, unlike Pixel Shaders, the CPU can successfully emulate Vertex Shaders.

The benefit to this is that it allows SiS to make the Xabre GPU less complex (and therefore cheaper) while still being able to run DirectX 8 software. However, offloading the geometry calculations to the CPU, which isn't optimised for this role, will drastically affect performance. The GeForce4 Ti, for example, features twin Vertex Shader units - one of the reasons for its superior performance compared to the GeForce3.

This was borne out in our tests, with the Xabre400 scoring 1.12, roughly equivalent to a GeForce4 MX 460. OpenGL performance, in particular, was disappointing, scoring just 29.4fps (frames per second) in Serious Sam at 1,280 x 1,024 in 32-bit colour. That said, the 3DMark2001 score of 4,298 at the same settings is good, especially considering the low price of £76. However, it's worth pointing out that we noticed a few graphics artefacts during testing, probably due to the early state of the Xminator XP unified drivers.

Another interesting feature of the Xabre400 is that it's the first graphics card we've seen to support the forthcoming AGP 8x specification. The current standard in modern motherboards is AGP 4x, delivering about 1Gbyte/sec of bandwidth between CPU/memory and the graphics card. AGP 8x doubles this to 2.11Gbytes/sec, potentially reducing bottlenecks.