(^256) PC Hardware: A Beginner’s Guide
2D and 3D Graphic Data
As you might guess, the transform and lighting processes used to generate 3D graphics
are much more complex than those used to generate 2D graphics. 3D graphics also require
and use considerably more computing resources as well.
To create a 2D image, the color, brightness, and placement (X and Y coordinates) of
each pixel must be generated. The X and Y coordinates of the pixel are the 2Dsofthe
graphic data. The X coordinate specifies the horizontal (side to side) placement, and the Y
coordinate places the pixel vertically (top to bottom) on the screen.
Of course, 3D images have a thirdD. In addition to horizontal and vertical placement,
each pixel also has depth. In a 3D image, a pixel can be made to appear to be closer or further
from the viewer with brightness and the attributes of surrounding pixels. To create this
effect, the video card must address the X and Y placement of a pixel as well as the values
that result in the pixel appearing to be in front or behind another pixel.Converting Digital to Analog
Once the graphics data has gone through the setup phase, it is stored in the video card’s
memory. The video RAM is also called the frame buffer because it holds the instructions
for each video frame as a buffer between the processing phases and the process that
converts the digital data into the signal required by the monitor.
The RAMDAC (RAM digital to analogy converter) may well be the most important
component in the entire process. In spite of the fact that it sounds like a character in a very
bad science fiction movie, the RAMDAC converts the digital data stored in the video
card’s RAM into an analog signal that is used by the monitor to create images on the
screen. The RAMDAC constantly reads from the video card’s RAM, converts the data
into an analog signal, and sends it on to the monitor. Remember that the graphic data is
being refreshed about 70 times a second, so most of the data being sent to the monitor
merely refreshes the display without changing it.Pathways and Converters
Regardless of where the transform and lighting phase is performed, the CPU and video
card must communicate with each other. On most PCs, this communication takes place
over one of two interface bus structures: the Accelerated Graphics Port (AGP) bus or the
Peripheral Component Interconnect (PCI) bus. More on these bus structures later in this
chapter (as well as in Chapter 11).Video Card Standards
The video display capabilities of the very first PCs did not include graphics. The IBM PC
and PC XT used the Monochrome Display Adapter (MDA) that displayed only text on a
monochrome (one-color) monitor. Because text only was much too confining, the