SiS swings Xabre at GeForce4 MX

COMPUTEX — At my meeting with SiS yesterday, I learned some interesting things about SiS's new Xabre GPU. SiS manufactures this puppy themselves at their own foundry using 8-inch wafers and a 150nm fab process. They're billing Xabre as a true DirectX 8-compliant part, and they're pricing it to compete with NVIDIA's GeForce4 MX and ATI's Radeon 7500, both of which lack the vertex and pixel shaders required for true DX8 compliance.

The Xabre in action
However, contrary to its billing, SiS's sword-like wonder doesn't have a vertex shader unit. Instead, SiS uses Microsoft's DirectX 8 software vertex shader, in which the host CPU does all the work. Maybe I've been living under a rock somewhere, but this one was news to me. Xabre does have a pixel shader unit with 29 instructions in its instruction set.

How the Xabre stacks up, technologically, against the GF4 MX and Radeon 7500 is a little bit murkier now. Both the GeForce2 and Radeon (and hence the GF4 MX and Radeon 7500, in which the 3D bits are the same), included a a sort of proto-pixel shader capability—NVIDIA called them register combiners—which can handle some DX8-class effects. Also, both of those chips can use DX8's software vertex shaders as needed.

Still, SiS's choice here is logical, since emulating hardware pixel shaders in software isn't entirely possible, while software vertex shaders work pretty well. So the Xabre still looks like a compelling entry in the mid-to-low-range graphics market. Assuming even a fraction of the companies showing Xabre cards here actually brings those cards to market (and much depends on pressure from NVIDIA and ATI, frankly), little SiS's Xabre could prove pretty sharp. I've seen cards from Gainward, Biostar, Soyo, Triplex, and Gigabyte, among others.

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