Video Graphics card – The graphics card plays an essential role in the PC. It takes the digital information that the computer produces and turns it into something human beings can see. On most computers, the graphics card converts digital information to analog information for display on the monitor; on laptops, the data remains digital because laptop displays are digital.
Video Card- An adapter card used to manage the display on the monitor.
Here are the three basic components of a graphics card and what they do:
1. Memory: The first thing that a graphics card needs is memory. The amount of memory on a display adapter is a major factor in determining the screen resolution and color depth that the card can manage. Just as with system RAM (random access memory), the video memory must be able to operate at a speed that can keep up with the processor and the demands of the system clock. The memory holds the color of each pixel. In the simplest case, since each pixel is only black or white, you need just 1 bit to store each pixel's color. Since a byte holds 8 bits, you need (640/8) 80 bytes to store the pixel colors for one line of pixels on the display. You need (480 X 80) 34,800 bytes of memory to hold all of the pixels visible on the display. If the display adapter is too slow at updating the image on the monitor, the user is left waiting or is presented with jerky mouse movements and keystrokes that appear in delayed bursts rather than as typed.
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2. Computer Interface: The second thing a graphics card needs is a way for the computer to change the graphics card's memory. This is normally done by connecting the graphics card to the card bus on the motherboard. The computer can send signals through the bus to alter the memory.
3. Video Interface: The next thing that the graphics card needs is a way to generate the signals for the monitor. The card must generate color signals that drive the cathode ray tube (CRT) electron beam, as well as synchronization signals for horizontal and vertical sync. Let's say that the screen is refreshing at 60 frames per second. This means that the graphics card scans the entire memory array 1 bit at a time and does this 60 times per second. It sends signals to the monitor for each pixel on each line, and then sends a horizontal sync pulse; it does this repeatedly for all 480 lines, and then sends a vertical sync pulse. The time required to complete a vertical pass is called the vertical refresh rate (VRR); the time required to pass once from left to right is known as the horizontal refresh rate (HRR). Generally speaking, faster is better. If the vertical rate is too slow, it can cause flicker, which is not only annoying, but can lead to eye strain. The larger the CRT, the faster the refresh rate must be to cover the entire area within the amount of time needed to avoid flicker. At 640 × 480 resolution, the minimum refresh rate is 60 Hz; at 1600 × 1200, the minimum rate is 85 Hz. Both the monitor and the display adapter produce the refresh rate.
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