3dfx Voodoo4 4500 & Voodoo5 5500 Preview

3dfx sent us what they call a beta revision of the final Voodoo5 5500 AGP card.  The revision of the VSA-100 silicon on this board is internally referred to as A2 and is running at 166MHz.  While 3dfx made it a point to tell us that this was not a final production sample, you also have to take into account common sense and realize that 3dfx has to have production quality silicon ready now, if not by the beginning of May, if they expect these boards to be shipping at the end of May. 

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Our take on the situation is that you can’t expect the hardware to get much faster than what we have here now; the main points for improvement will be in the drivers.  At this point, it is highly unlikely that the shipping VSA-100 chips will feature a much higher clock speed than 166MHz unless 3dfx has been hiding something from us. 

The board we were provided with, as mentioned above, was a Voodoo5 5500 AGP, which features two VSA-100 chips and a total of 64MB of SDRAM also clocked at 166MHz.  Because the two chips are working together in SLI (Scan Line Interleave) mode, the 64MB of memory is split evenly between the two, and since they are essentially independent of one another, the textures in any scene must be duplicated in each set of 32MB of SDRAM.  This means that if you have a scene with 10MB of textures, it occupies a total of 20MB of memory out of the 64MB on board since each chip requires those 10MB of textures to be available to it locally. 

Each chip has its own 128-bit pathway to its 32MB of SDRAM, meaning that each chip has the bandwidth of an SDR GeForce 256.  When put together, the card theoretically has about 5.3GB/s of available memory bandwidth, but you have to take into account that textures must be duplicated in both 32MB sets, meaning that some of that bandwidth is wasted (although the amount wasted should be very little). 

Each chip can render two single textured pixels per clock or one dual textured pixel per clock.  This gives a single VSA-100 chip a fill rate of 333 megapixels per second when dealing with a single textured game, or 166 megapixels per second when running a dual textured game.  For the Voodoo5 5500 AGP, this results in a fill rate of 667 megapixels per second for a single textured game or 333 megapixels per second for a dual textured game.  Seemingly ages ago, when single textured games were the only things available, this sort of a fill rate made the most sense but as most of today’s games are dual textured, this sort of flexibility is not as useful as it once was. 

Don’t you find it interesting that the most talked about fill rate on the Voodoo3 3500 was its 366 megatexels per second fill rate and not its 183 megapixels per second fill rate, whereas the exact opposite exists today with the Voodoo4/5?