HyperZ II/Card details

Occlusion culling

HyperZ-II is found onboard Tachyon as well, as with all RV250 based boards. Besides a variable rate lossless Z-Buffer compression, a hierarchical Z-buffer is the primary feature of this. ATI's implementation of this uses 8x8 pixel blocks for hierarchical Z-buffering. The nearest vertex value from the 8x8 block is taken and compared to a stored reference value. This comparison tests to see whether any of the pixels within the block are visible. If the nearest pixel in the block is deeper than the reference value, the pixel block is discarded. If the vertex is nearer than the reference value, the block is rendered.

This implementation of occlusion culling presents both certain advantages and disadvantages. In its favor, hierarchical Z-buffering is highly advantageous in memory bandwidth consumption. Being that the entirety of the block is compared on chip to the stored reference value, there is little access to external memory. On the negative side, if only a single pixel is visible the entire block must be rendered.

The Tachyon G9000 card

Tyan Tachyon G9000 Pro card

Tyan’s Tachyon G9000 Pro closely follows ATI’s RADEON 9000 PRO reference design. Components are placed identically, which isn’t surprising considering that the dual 400MHz DACs, TV encoder, and other video circuitry are now integrated on the RADEON 9000 core itself. As a result there isn’t much card manufacturers such as Tyan can do to make their products stand out from each other.

With the Tachyon 9000 Pro sharing the same reference design as ATI's incarnation, both boards share the same connections. Included are the standard SVGA connection, as well as DVI and video out. Through the SVGA and DVI connection, dual displays can be connected through what ATI terms their HYDRAVISION software. Additionally, video output is included with an adapter allowing for both composite and S-video out.

Overclocking

Overclocking the Tachyon proved fairly painless. Loading up a third party overclocking utility such as Powerstrip, it was not an issue to pull a few more frames per-second out of the board. When overclocking the core, Tachyon did find itself with a potential advantage in that it provided an overall better active cooling system than Radeon 9000 Pro. The heatsink onboard Tachyon was roughly double the size of ATI’s RADEON 9000 PRO card, providing more efficient heat removal.



Running Tachyon at 290/290 did not produce any apparent artifacting or stability issues. Fill-rate levels were increased somewhat, as was overall performance.