Transform and Lighting
Drawing those polygons
Transform and Lighting processing, simply often called "geometry processing," is the part of the 3D rendering process that does the calculations for the 3D position of each polygon and processes the effect of dynamic lights in a 3D scene. In short, the better your transform and lighting unit is, the more detailed the objects in a game will be and the more advanced the lighting effects.
On most PCs, T&L is done in software by a general purpose CPU such as an AMD Athlon or Intel Pentium III. Since the CPU is involved with numerous other tasks such as memory management, input processing, and score keeping, the real-world performance is approximately 1-2 million sustained polygons/sec. The Dreamcast follows this design paradigm by using a Hitachi SuperH-4 RISC processor. However, since the SH-4 isn't expected to perform as a database server in the same way that an AMD or Intel CPU must, Sega was able to select a CPU that offered faster floating-point operations at the expense of "business- performance." Sega claims that the Dreamcast is capable of doing "more than 3 million polygons/sec" while some developers have claimed "4 million polygons/sec" but without any independent benchmarks, it's hard to separate the marketing from the truth. Based on currently shipping games in the US and in Japan, real-world performance is approximately 2-3 million polygons/sec depending on the additional calculations required. When it comes to T&L however, the Dreamcast currently outperforms anything Intel and AMD is offering.
Enter the GPU
However, the engineers and innovators at Nvidia were not content with the lackluster performance of the PC and introduced an idea that their marketing likes to call the "GPU," or graphics-processing unit. The significant advancement brought with Nvidia's GeForce 256, is on-board transform and lighting. The T&L unit in the GeForce is rated at 4-5 million polys/sec (Nvidia claims 15 million vertices
/sec) with 8 lights in hardware. Although the limits of performance for the GeForce are difficult to assess with current benchmarks, the GeForce 256 is generally faster than the SH-4 in the Dreamcast, and the ability to calculate 8 dynamic lights per poly is something that the Dreamcast is unable of doing. Unfortunately, as Nvidia is the only manufacturer with a shipping T&L unit (with S3 to follow shortly) most of the power is left idle. Even products designed for "hardcore gamers" such as the ATI Rage Fury Maxx, for example, do not include hardware T&L and instead focus on making today's games faster. Developers cannot create economically successful games if their products will only run on one manufacturer's product. In simple terms, most software developers still take "software T&L" as their target platform. Think of the situation on the PC as a BMW Z8 stuck in rush hour on the 101 freeway and the Dreamcst being an import Acura Integra on a private racetrack.
A bump in the night
Although only currently supported by Matrox, environment mapped bump-mapping is an impressive feature that can be used to simulate higher polygon models. A young child can tell you that a person would not be able to see without any light, and this same elementary principle that makes bump mapping work. When you look at the texture and detail of something fabric, the texture is present because of the way light creates tiny shadows and highlights as it bounces of the non-uniform surface. If you were to model fabric in the most accurate way, you'd have to literally model each thread individually. Unfortunately, this would also increase the load on the T&L unit to unrealistic proportions. Bump-mapping, circumvents this problem by taking a flat surface composed of only a few polygons and then applying "bump-map" which essentially distributes the light non-uniformly. Environment mapped bump-mapping is just one method of bump-mapping.
So which is better?
The PC has the better technology for delivering high-detail 3D models through fast transform and lighting as well as environment mapped bump-mapping. This only makes sense as the GeForce 256 is just made its way onto store shelves this month whereas the first Dreamcast shipped over a year ago in Japan. The Dreamcast was actually around before the TNT2 was even announced! Unfortunately for the PC, most of this extra power is left untapped and in many cases, games developed for Dreamcast will generally look better than their PC counterparts.