Many brands of graphics controller cards are out there, but almost all the core video chipsets-the integrated circuits that contain the graphics BIOS and processor-are made by a small number of companies. Like BIOS chips on motherboards, the make and model of the video chipset is often at least as important as the maker of the card. In general, two different graphics controller cards with identical chipsets and the same amount of memory have very similar performance, even if they were made by different manufacturers.
The vast majority of new video cards have chipsets from either ATI or NVIDIA. ATI makes their own branded video cards and also sells chipsets to other manufacturers, and NVIDIA is strictly a parts supplier to other manufacturers. Both companies offer a broad range of chipsets at many performance levels. ATI is now owned by the CPU maker AMD, but their graphics processors work equally well with Intel CPUs. A few other companies, including Matrox, VIA, and AGEIA, also make video chipsets, but ATI and NVIDIA products are the most common.
Most laptop computers and many desktop systems come with graphics controllers built into the motherboard. Some of these graphics processors are supplied by ATI or NVIDIA, but Intel and other chip makers also produce processors for this market.
Trying to understand the difference among different video chipsets is even more confusing than comparing different kinds of CPUs. As a general rule, the performance of both ranges improves as the model number of the chip increases, but there are exceptions. The best way to compare different types is to read the specifications on individual graphics controllers, consult the chip makers' Web sites (http://www.nvidia.com and http://www.ati.com), and read reviews in magazines and independent Web sites.