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DeltaChrome S8: First look

Getting warmer

WE PREVIEWED S3's new DeltaChrome graphics chip exactly three months ago. At the time, the DeltaChrome looked like it could become a competent alternative to ATI and NVIDIA's two-fisted stranglehold on the DirectX 9 graphics market. Instead of looking to challenge for the high-end graphics crown, S3 was preparing a line of mid-range and low-end DeltaChrome products that would balance 3D performance and DirectX 9 compatibility with a suite of new video features and high-definition video output.

On paper, DeltaChrome looked pretty good, but we all know that paper specs and features don't always fly in the real world.

Although cards based on DeltaChrome won't be available in the real world until next year, S3 has given us a chance to preview of the chip's 3D graphics capabilities using an early DeltaChrome S8 sample board with the latest beta drivers from S3. How does the S8's 3D performance look at this early stage? Read on to find out.

The DeltaChrome S8: A quick refresher course
If you haven't already, take a moment to read through our initial DeltaChrome preview. Since we'll only be previewing the chip's 3D capabilities today, I'll only cover features related to the 3D pipeline. The DeltaChrome has plenty of other goodies that branch from and extend beyond its graphics pipeline, and we'll cover those with a full review once retail boards become available.

GPUS3 DeltaChrome S8
Core clock300MHz
Pixel pipelines8
Peak pixel fill rate2400 Mpixels/s
Texture units/pixel pipeline1
Textures per clock8
Peak texel fill rate2400 Mtexels/s
Memory clock300MHz
Memory typeBGA DDR SDRAM
Memory bus width128-bit
Peak memory bandwidth9.6GB/s
PortsVGA, DVI, composite and S-Video outputs
Auxiliary power connectorNone

With eight full pixel pipelines running at 300MHz, the S8 boasts plenty of fill rate. The chip's 128-bit memory interface is reasonably competitive with the Radeon 9600 Pro and GeForce FX 5700 Ultra. However, unlike the sophisticated crossbar memory controllers employed by ATI and NVIDIA, the DeltaChrome's memory controller can only access data in 128-bit blocks.

The chips in the DeltaChrome line are all DirectX 9 compatible and include full support for pixel and vertex shader versions 2.0. Pixel shader precision maxes out at 96 bits per pixel, or 24 bits of precision for each of the red, green, and blue color channels, just like ATI's R3x0 graphics chips. DeltaChrome's pixel shaders support 128 color instructions per pass, with up to 32 texture instructions and 16 texture lookups, but they can't branch and loop like NVIDIA's flexible GeForce FX pixel shaders. DeltaChrome's pixel shaders do, however, support per-pixel gamma correction.

Since drawing unseen pixels is a waste of valuable resources, the DeltaChrome employs several methods to reduce overdraw. In addition to occlusion culling algorithms that discard hidden pixels early in the rendering pipeline, the DeltaChrome minimizes Z-buffer reads and writes and has a zero-cycle Z-clear. The chip also has some additional overdraw reduction technologies under the hood, but S3 is keeping the details to itself.

Though we won't be exploring the S8's antialiasing or anisotropic performance today, the DeltaChrome supports both in hardware. Anisotropic filtering is supported up to 16X, and 4X multi-sampled antialiasing is available at resolutions up to 1024x768. It doesn't appear that either aniso or AA is available in the current drivers, though.

Amazingly, S3 has managed to squeeze all those features onto a chip with somewhere between 60 and 80 million transistors (for comparison, ATI's eight-pipe R300 graphics chip weighs in at roughly 110 million transistors). S3 has chosen TSMC to produce the DeltaChrome S8 chip using its 0.13-micron fabrication process.

S3's DeltaChrome S8 evaluation sample

Anatomy of a sneak peek
Our early DeltaChrome S8 sample came with beta drivers¬ónot exactly a recipe for smooth sailing, as one might expect, since we're dealing with a brand-new graphics core from company that's been out of the game for a few years. We came across a number of apparently driver-related issues with image quality, performance, and compatibility. For instance, the S8 wouldn't cooperate with our nForce3-based graphics testing platform. We also found problems with Call of Duty and with our real-time high dynamic range lighting demo, so we weren't able to benchmark the card with those apps. (Of course, such problems are a frustratingly intractable part of the graphics game. ATI just released drivers with a fix for Call of Duty, and NVIDIA's cards have never supported that real-time lighting demo properly.) S3 is already working on fixes for these issues.

Also, S3 readily admits that the card's OpenGL drivers aren't quite up to speed yet, but OpenGL performance is expected to improve dramatically with the next major driver release.

S3 has time to perfect its DeltaChrome drivers before cards are available to the public next year, so we remain hopeful. However, some of the problems we encountered do need to resolved before the DeltaChrome is ready for commercial sale. S3 has been working closely with us since we started testing the S8, and judging by the response, we're fairly confident they'll have the issues sorted out by the time consumers can actually get their hands on cards.

Not exactly a production board, folks