Machine Design

Graphics Accelerators

Several suppliers of graphics accelerator boards for PCs now claim their products will bring high-performance, 3D graphics to PC platforms. Among the high-end graphics features that these products provide are 24-bit depth buffers, large frame buffers on the order of several megabytes.

Prices of such boards have come down partly because the digital-to-analog converter used to produce display signals has been combined with the display processor and clock synthesizer on a single chip. Boards using such chips tend to cost between $150 to $225. Also lowering costs is the use of new types of DRAM (dynamic random access memory) chips which are more dense than older versions. Some less-expensive boards cut costs by not using dual-ported video RAM. The restriction is that either the graphics controller or the display processor can access display data, but not both at the same time. This may limit refresh rate, resulting in flicker for high density (1,024 768 with 24-bit color) displays. There is less likely to be a difference between the two types of boards for ordinary 800 600 VGA displays, however. Boards with video RAM are particularly important for graphic-intensive uses such as multimedia and desktop publishing. However, the amount of video RAM required for such applications tends to be large, probably more than the 2M bytes of video memory found on base configurations of such products.

Increasing use of digital video for high-end multimedia applications may make graphics accelerators more important for PCs. Some boards now come with slots able to accept digital video accelerator chips now on the drawing boards, which work with the graphics accelerator to decompress and scale video information. High-end graphic accelerator boards (costing on the order of $1,000) support 3D operations such as Gouraud shading, for producing shaded images of wire-frame models.

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