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Preview: S3's DeltaChrome S4 Pro GPU

S3 goes after the value market
— 11:10 AM on July 14, 2004

MORE THAN 10 MONTHS ago, S3 began its PC graphics comeback with DeltaChrome. Decked out with DirectX 9 support, 24-bit pixel shaders, and component HDTV output, DeltaChrome looked pretty sweet. Unfortunately, immature drivers and stiff competition conspired to ruin the eight-pipe S8's coming out party. S3 had difficulty attracting board makers to sell cards based on its GPU, especially in North America. Over time, S3 improved its drivers and released the DeltaChrome S8 Nitro with higher clock speeds and more competitive performance, but the card still couldn't keep up with ATI and NVIDIA's updated mid-range lineups.

Despite not taking the mid-range graphics market by storm, the DeltaChrome S8 Nitro proved that S3 could produce a solid DirectX 9-class graphics part with competitive capabilities. With that newfound legitimacy, S3 has set out to tackle the value market with a four-pipe version of the DeltaChrome dubbed the S4. The DeltaChrome S4 brings S3's DirectX 9-class shaders and component HDTV output to lower price points, but is the DeltaChrome S4 fast enough to take on ATI and NVIDIA's low-end offerings? We've compared a DeltaChrome S4 Pro with a GeForce FX 5200 Ultra and Radeon 9550 to find out.

The DeltaChrome S4 Pro reference card

The S4 GPU
Apart from a few minor efficiency tweaks, the DeltaChrome S4 graphics core is essentially a DeltaChrome S8 divided by two. We've covered the S8 extensively here at TR, and I recommend you take a look at Damage's original DeltaChrome preview and my first look at the DeltaChrome S8 for the nitty gritty details on S3's graphics technology. I'll highlight some of the S4's more notable features below.

The S4 Pro GPU

Weighing in at half a DeltaChrome S8, the S4 has four pixel pipelines and two vertex shaders. S3 is quick to point out that these are real hardware vertex shaders, not software-drive units that run vertex shader programs on a system's CPU.

Like the S8, the S4 is a true DirectX 9-class design that meets Shader Model 2.0 requirements. DeltaChrome even exceeds SM 2.0 requirements in a few areas. SM 2.0 only demands hardware support for a maximum of 64 color instructions, 96 instruction slots, and 96 runtime instructions. However, DeltaChrome supports up to 128 color instructions, 160 instruction slots, and 160 runtime instructions. NVIDIA's GeForce FX also exceeds the Shader Model 2.0 spec, but most applications are written and compiled for SM 2.0 hardware. Budget cards like the S4 likely won't have the horsepower to run longer shader programs in real time, anyway.

Speaking of shaders, the DeltaChrome S4's pixel shaders offer 24 bits of floating point precision for each color channel, just like ATI's R3x0 GPUs. As we've seen with NVIDIA's GeForce FX 5200 GPU, mucking around with partial precision and integer data types can potentially sacrifice image quality, so it's good to know the S4 will deliver 24 bits all the time.

Apparently pleased with what TMSC's 0.13-micron fabrication process did for the DeltaChrome S8, S3 is using the same foundry and fab process to produce the DeltaChrome S4. The S4 graphics core weighs in somewhere between 35 and 45 million transistors, which is fewer than the claimed transistor counts of ATI and NVIDIA's low-end GPUs, although methods of estimating such things vary from one company to the next.

Memory clocked at 300MHz

The DeltaChrome S4 will be available in two flavors, the S4 and the S4 Pro. The S4 Pro, which we'll be looking at today, comes with core and memory clock speeds of 300MHz and a 128-bit memory bus. S3 hasn't nailed down clock speeds for the vanilla S4 yet, but they expect them to be between 250 and 275MHz. Add-in board partners will also be free to build low-end S4 cards with a 64-bit memory bus, though S3 is making a 128-bit memory bus available in all S4 chips. S3 also wants to ensure that ensure that 64-bit cards are clearly labeled to avoid consumer confusion.

Our S4 Pro reference card came with 128MB of DDR memory onboard, though the S4 also supports 64 and 256MB configurations. Add-in board partners may opt to use either TSOP or BGA memory chips, but we're unlikely to see the latter in the budget segment.

Native HDTV support
DeltaChrome's native component output support is unique enough to deserve its own subheading. Like the S8, the S4 supports all 18 ATSC High Definition Standard resolutions, including 1080i, 1080p, and 720p.

S3's component output dongle

Among budget graphics cards, the S4's native HDTV output capabilities are unique. Best of all, HDTV output will be available on vanilla S4 and S4 Pro cards alike. To get HDTV output from ATI or NVIDIA, you have to spring for pricier All-in-Wonder or Personal Cinema products. ATI also sells an HDTV output adapter, but it'll cost you $30 and occupy an open VGA port.

Component output makes the S4 look ideal for home theater PCs, but as more HDTVs support VGA and DVI inputs, the value of component outputs may dwindle. For now, though, it looks like component output could be the S4's ace in the hole.