Chapter 12: Video Cards^269
Video System Resources
Unlike other peripheral devices mounted inside the PC’s case, video cards do not con-
sume much in the way of system resources. Not all video cards use an IRQ. Those video
cards that do use an IRQ use one of the pair set aside for PCI devices (IRQ 11 or IRQ 12).
All VGA-compatible video cards, which are virtually all of them, use a standard pair of
I/O port addresses (3B0–3BBh and 3C0–3DFh). Manufacturers of other types of expan-
sion cards avoid these addresses, which eliminate possible conflicts during installation.
Video Device Drivers
The video card’s device driver translates the images generated by an application pro-
gram into instructions that the GPU can use. Where the software may consider the dis-
play as a collection of pixels, the GPU sees it as a series of line and shape drawings, and
it’s the job of the graphics driver software to convert between the application’s vision and
that of the graphics processor.
Typically, there are separate graphics drivers for each resolution and color depth combi-
nation the video card supports. Because it uses a separate piece of software for each unique
combination of settings, the video system may not perform the same on different resolution
and color depth settings. The same may be true of the different drivers used for each operat-
ing system for a particular video card. Video drivers are frequently updated, so if optimum
video performance is your thing, check the manufacturer’s Web site frequently.
Figure 12-6. A motherboard with PCI and AGP interface slotsPCI Expansion SlotsAGP Port