Kyro II Specifications
The GPU is engraved in 0.18Ķ instead of 0.25Ķ for the first Kyro GPU and is clocked at 175 MHz against 125 MHz for the PowerVR. It comes with only 15 millions of transistors (when 25 millions of transistors are aboard the GeForce 2 MX) and its fillrate seems to be ridiculous when compared to competing products: with only 350Mpixels/s and 350MTexels/s youíre surely wondering how the Kyro II can beat a GeForce 2 GTS! Well the answer lies in the Tile Rendering engine in which we will dig into later. Concerning the memory, when most of today high end graphics cards come with DDR memory, the Hercules 3D Prophet 4500 64 MB comes with 64 MB of SDRAM memory, in order to reduce costs (notice that the Kyro II GPU also supports DDR). The 128-bit memory bus offers a bandwidth of 2.6GB/s (against 4.94GB/s with a GeForce 2 GTS). Here are the exact features the GPU offer:
The Secret Weapon known as Tile Based Rendering
The Tile Based Rendering feature isnít really new since it first came out in 1995 but really change the deal since it brings high 3D graphics performance for a truly modest price. When nVidia has to include expensive high speed memory to deal with bandwidth problems, ST has chosen a truly & exclusive different approach. The idea of the Tile Based Rendering function comes from a simple statement: usually 3D chips render every pixel of a graphic scene even those that are hidden and later determine which one to display according to the Z value of each pixels. Tile Based Rendering aims to determine if a pixel is visible or not before rendering it, in order to save GPU bandwidth and horsepower. In a 3D scene with a depth complexity of 3D the gain of performance brought by the Tile Based Rendering can reach 65%! This feature also called HSR (Hidden Surface Removal) by some people is so interesting that it already equips the ATI Radeon GPU while it as been recently introduced in the nVidia GeForce 3 GPU (Z Occlusion Culling). However the Tile Rendering feature of the Kyro II is much more elaborated than the equivalents offered by competitors. When the Kyro II GPU renders a scene it cuts it in several blocks called tiles (of 32x16 pixels each). Then each tile is rendered separately before the small but sufficient enough 24 bits 12Kb Z-Buffer determines if the pixels in each block are visible or not. The great thing is that the onboard buffer can store every tiles so they arenít passed to the video memory, making sure performances arenít altered. By using this TBR process not only performances are better but the card avoids overdrawing since textures are only loaded for visible parts of a scene. The internal Z-Buffer can achieve up to 32 Z calculi per clock cycle. But thatís not all! Thankfully the Kyro II GPU doesnít contain only the Tile Based Rendering feature to enhance 3D operations.
8 Layers Multi Texturing
Before displaying the scene, the blending process has to be done. It is achieved in the internal Tile Buffer of the GPU. As a matter of fact the Kyro II can apply up to 8 textures on a single pixel, without needing a frame buffer, in one single pass. However due to the fact the Kyro II comes with 2 pipelines, applying 8 textures will require 4 clock cycles. Another thing to note is that as most of today games only use 2 or 3 textures per clock cycle, the benefits of the 8 layers multi texturing technology arenít obvious.
Internal True Color
Here is another very interesting feature of the Kyro II GPU. Every arithmetic operation (as well as the color blending) is done by the processor in 32 bits. The image obtained is then converted in 16 bits while it reaches the external frame buffer. As a result the quality of 16bits images is very high. Usually with traditional GPUs the fps performance drastically falls down when you switch from 16 bits to 32 bits but the Kyro II really kicks ass in this domain since its frame per second rate stays constant! Youíll barely notice any performance enhancement by rolling back in 16 bits.
First introduced by Matrox this 3D feature simulates a relief effect on textures by playing with lighting values in order to ensure the scene looks as natural as possible. The Kyro II supports three Bump Mapping modes: the most widespread Environmental Bump Mapping one as well as the Emboss Bump Mapping, and the Dot Product 3 Bump Mapping. There is no doubt that Environment-Mapped Bump Mapping is great to look at. But there is a small performance hit whenever you use it - but if you are into image quality instead of frame rates like I am, you'll love it.
Like every good 3D chip worthy of that name, the Kyro II supports the Full Scene Anti Aliasing in both 2x & 4x modes. The FSAA is used to remove every popping pixel or other scaled shapes on screen by super sampling the image to ensure a highly realistic level. To proceed the Kyro internally renders the scene in a resolution twice higher in height or in width (it corresponds to the 2x mode) or twice higher in both height & width. Then the image is reduced using special filters so it can be displayed on the screen. This method uses a lot of power and memory resources but thanks to the Tile Rendering, the Kyro II doesnít suffer a lot in comparison to nVidia chips.
Well thereís nothing special to say here except that the DVD support brought by the Kyro 2 isnít a real one. The chip features the Motion Compensation technology that represents a semi-hardware decompressing solution to play video DVDs. With the Motion Compensation Blending & Video Scaling the DVD playback is surely smoother but doesnít compete with a real hardware MPEG 2 decoder like the Creative DXR3 cards. Anyway itís always good to have a feature that helps playing DVDs on computers with weak performance even if weíd have preferred the Kyro II to come with a full hardware decoder like ATI Radeon cards. A last thing to consider is that PowerDVD 3 doesnít handle the Motion Compensation feature of the Kyro II contrary to WinDVD 2000.
The Kyro II supports the Bilinear, Trilinear & Anisotropic filtering processes and also supports the S3TC & DXTC textures compressing algorithms. If the Kyro II seems to be very complete in terms of 3D features thereís one major thing missing in it. Indeed as you have surely noticed the Kyro II doesnít come with a hardware Transform & Lighting engine. If actually this lack isnít tragic in most of today games (only a few games take advantage of the Transform & Lighting) we canít be sure that in tomorrowís games this wonít be a major drawback. However the drivers seem to emulate the T&L engine but this canít replace a real onboard calculus unit.