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PC Hardware in a Nutshell, 3rd Edition
book

PC Hardware in a Nutshell, 3rd Edition

by Robert Bruce Thompson, Barbara Fritchman Thompson
July 2003
Beginner to intermediate content levelBeginner to intermediate
874 pages
38h 13m
English
O'Reilly Media, Inc.
Content preview from PC Hardware in a Nutshell, 3rd Edition

Throughput

The overall throughput of a video adapter is constrained by the speed and architecture of its RAMDAC and video memory, and the number of bits that it processes per operation. The throughput required at any given combination of display settings is the product of four factors: resolution (how many pixels per frame), color depth (how much data per pixel), refresh rate (how many frames per second), and number of planes (one for 2D modes, and typically three or four for 3D modes). When a video adapter reaches its throughput limit, you can increase any of these factors only by reducing one or more of the others.

For example, a video adapter may have a RAMDAC that can process at most 225 million bytes/s. Operating in 2D mode, that adapter supports 1024x768 resolution at 24BPP and 85 Hz refresh. With those settings, the video adapter processes (1024 × 768 × 24BPP × 85 Hz = 200,540,160 bytes/s), well within the RAMDAC limits. Increasing resolution to 1152x864 requires (1152 × 864 × 24BPP × 85 Hz = 253,808,640 bytes/s), well beyond the capacity of this RAMDAC. To run 1152 × 864, you can either: (a) continue using 85 Hz refresh, but reduce the color depth from 24BPP to 16BPP (1152 × 864 × 16BPP × 85 Hz = 169,205,760 bytes/s), or (b) continue using 24BPP, but reduce the refresh rate from 85 Hz to 75 Hz (1152 × 864 × 24BPP × 75 Hz = 223,948,800 bytes/s).

Similarly, when the adapter runs in 3D mode, the requirement for three (or four) planes forces lower resolutions, color depths, ...

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Publisher Resources

ISBN: 059600513XErrata Page