Introduction: Hacks #68-74

Except for the CPU and memory, the video card handles more data more often than any other component in your PC. It's possible for a 1024768 display with a color depth of 32 bits (4 bytes) refreshed 60 times per second to move tens of megabytes per second—if the entire screen refreshed with new data at each screen refresh interval. This is a lot of data, and it does not include the processing and rendering the video card's CPU has to handle to generate a constantly dynamic display. Enhancing video performance is most important to graphic designers and gamers, but it can also make Windows less sluggish and clunky for the rest of us.

Overall video performance is affected not only by the speed, quality, and features of the video adapter card (which in some cases you may overclock just as you can your CPU and system RAM) but also by which I/O interface your video adapter uses—ISA, PCI, or AGP (including video adapters built onto the system board).

The ISA and PCI buses can be used for just about every type of I/O device there is, from modems to network to video adapters. A lot of activity is going on within these buses. The 16-bit (2-byte wide) ISA bus runs at 16 MHz, yielding a maximum throughput of 32 megabytes per second (MBps). The 32-bit (4-byte wide) PCI bus runs at 33 MHz, yielding maximum throughput of 133 MBps.

The AGP bus is dedicated specifically to graphics—a straight pipe from the PC's CPU to the display—and it's fast! The 64-bit-wide (8-byte) AGP bus runs at 66 MHz, providing 266 MBps throughput; AGP 2x's throughput is 533 MBps; AGP 4x's is 1.1 GBps (gigabytes per second); and AGP 8x yields 2.1 GBps throughput, all of it dedicated to graphics. By all means, if you are still using an ISA bus video adapter, it is time to upgrade to at least a PCI adapter, if not a new system board and AGP video.

The hacks in this chapter are all about getting and maintaining the highest video throughput numbers you can, which will affect both 2D normal desktop appearance as well as 3D graphics. Data bus throughput numbers are important because the data has to get from the CPU to the video adapter somehow—the faster the better. In rare cases, overclocking may achieve a 50% increase in video performance, but a 10-20% increase is typical.

The real measure of video performance lies in the results of various benchmark tests, such as the free FutureMark (http://www.futuremark.com) 3DMark test suite. This is the most popular among those who will do nearly anything to boost graphics performance: gamers.

Within 3DMark and similar tests are measurements of several graphics performance qualities. Specifically, the number of pixels (picture elements) processed per second is evaluated for 2D performance testing, and the number of texels (texture elements) processed per second (measured in millions of texels) is evaluated for 3D performance testing. The higher the texel and pixel test results are, the better.

Pixels are the individual dots of light you see on your computer screen, made up of a combination of the three colors used by your video display (red, green, and blue). The data that creates the appearance of each pixel consists of a pixel address (in row and column) and how intense each color is to be. The color depth, or resolution, you can obtain depends on how much data is used to define the brightness of the colors, from 8 bits (256 colors) to 32/24 bits (16.8 million colors—8 of the 32 bits are used for a transparency layer called the alpha channel) and even higher. High pixel data transfer performance is important for overall text and graphics display speed and appearance. Texels are pixels that are given special attributes that help produce a three-dimensional appearance of depth and are treated differently in video data processing to provide this effect; thus it is important to have high texel performance to avoid clunky and rough-looking 3D.

Full-motion video benchmark tests are used to evaluate the video frame rate—our current standard is 24 frames per second—as we see in big-screen movies. Normal broadcast and cable television images refresh the screen twice at 60 times per second, yielding a picture that is completely refreshed at 30 screens or frames per second. In video gaming, the mantra is "Frame rate is everything." The closer our PC's video performance gets to live TV, the better (and better yet if it can exceed TV).