Understanding Graphics Cards: Components and Functionality

The Graphics Card

1. What are Graphics Cards?

A graphics card is the hardware component of a computer that generates the image displayed on the monitor. The graphics card has evolved from a mere interface between the microprocessor and the display, which simply translated information consisting of an 80x24 character screen into an analog signal compatible with the monitor, to managing images with resolutions of 1024x768 pixels or more, with millions of possible colors and refresh rates over 70 Hz.

Current graphics cards have their own dedicated CPU for graphics operations and their own RAM, whose capacity is approaching and may even exceed that of the system.

2. Components of a Graphics Card

A graphics card has three main components:

• The graphics chipset
• The RAM
• The RAMDAC

The Graphics Chipset

The graphics chipset is the integrated circuit that performs the core operations of the graphics card. Due to heating issues, most incorporate a heatsink or a fan mounted above it. The main chipset manufacturers are Intel, ATI, nVidia, and Matrox.

The RAM

The graphics card has its own RAM memory area where it stores images to send to the monitor. This memory area is also used by the chipset to perform its calculations and operations. Current video display boards have between 128 MB and 1 GB of RAM. The graphics card's RAM is typically of the SDRAM type.

Color depth is the number of bits that contain information about the color of each pixel. Normally, color depths of 8, 16, 24, or 32 bits are used. The memory occupied by an image of 1024 x 768 pixels and a 16-bit color depth is: 1024 x 768 x 16 = 12,582,912 bits = 1.5 MB.

The RAMDAC

The mission of the RAMDAC is to convert the image information that is in the RAM of the graphics card into analog signals that will be sent to the monitor. The capacity of the RAMDAC determines the maximum resolution, color depth, and refresh rate that a graphics card can support.

For example, a resolution of 1024 x 768 and 32-bit color occupies 3 MB of RAM. If we want a refresh rate of 85 Hz, the RAMDAC will have to be able to read 3 MB of RAM 85 times per second. That is, the RAMDAC should be able to access the RAM at a speed of: 3 x 85 = 255 MB/s.