The RAMDAC
The RAMDAC (RAM digital to analog converter) solves the simple problem that the PC
and video card are digital and the monitor is an analog device. The information stored in the
video memory is digital data that must be converted into an analog signal before it can be
used by the monitor to create the display image.
The RAMDAC reads data from the video memory, converts it to an analog signal
wave, and then sends it over the connecting cable (the one connected from the back of the
PC to the monitor). The RAMDAC has a direct impact on the quality of the screen’s im-
age, how often the screen is refreshed, the color palette used, and the resolution and color
depth used in the display.
There is a DAC (digital to analog converter) for each of the three RGB (red, green, and
blue) colors that are used together to create the right color mix for each pixel. The speed of
the RAMDAC has a lot to do with how well it is able to support the quality of the display.
Today, a fast RAMDAC has a rating between 300MHz to 350MHz, but then in 1999,
150MHz was fast.3D Graphics
The video displayed on the monitor is actually a very fast moving set of still images. It is
very much like an electronic flipbook—the more images that the PC can display in a sec-
ond, the smoother the images or actions on the screen will appear. The higher the frame
rateonthevideocard,thefasterthecardperformsthetransformandlightingprocesses.
3D applications, such as games and animations, generate data that reflect everything
going on in a game. This data reflects the action of the software in terms of mathematical
data, including camera (the user’s viewpoint) movements, the movement of objects in
relationshiptootherobjects,thecalculationsofthephysicsengine(howobjectsmoveand
interact), and any other factor affecting the display and the simulated action taking place.
Typically, this data is filtered through the graphics language’s API and then sent to the
video RAM for processing through the transform, lighting, and setup phases. You may
find references that refer to the entire process as the 3D pipeline, which also includes the
rendering phase.3D Graphics Accelerators
The 3D images displayed on a PC monitor are actuallysurface modeling, a process that
creates the illusion of a three-dimensional scene on a 2D (flat) surface. Surface modeling
represents 3D objects using a mesh of polygons, typically triangles, to create images with
their outside edges. If enough triangles can be used to create an image, even the curved
surfaces can be made to look smooth on the PC’s display. A variety of geometric descrip-
tions is used to define each triangle, including its vertices (corners), vertex normals
(which side is pointing out and which is inside to create shading), reflection characteristics(^270) PC Hardware: A Beginner’s Guide