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Introduction
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.
RADEON™ 64-MB AGP Graphics Card
If you look at the screen of a typical PC very closely, you can see that all of the different things on the screen are made up of individual dots. These dots are called pixels, and each pixel has a color. On some screens (for example, on the original Macintosh), the pixels could have just two colors -- black or white. On some screens today, a pixel can be one of 256 colors. On many screens, the pixels are full-color (also known as true color) and have 16.8 million possible shades. Since the human eye can only discern about 10-million different colors, 16.8 million colors is more than enough for most people.
The goal of a graphics card is to create a set of signals that display the dots on the computer screen. If you have read How Computer Monitors Work and How Television Works, you have a good sense of what those signals are and how a monitor turns them into light.
By helping of HowStuffWorks, we'll learn all about graphics cards and how they optimize your PC experience.
Graphics Card History and Standards
The first graphics cards, introduced in August of 1981 by IBM , were monochrome cards designated as Monochrome Display Adapters (MDAs). The displays that used these cards were typically text-only, with green or white text on a black background. Often, the graphics card had a printer port, since the printer would print the same data shown on the low-resolution "green" screen. Color for IBM-compatible computers appeared on the scene with the 4-color Hercules Graphics Card (HGC), followed by the 8-color Color Graphics Adapter (CGA) and 16-color Enhanced Graphics Adapter (EGA). During the same time, other computer manufacturers, such as Commodore, were introducing computers with built-in graphics adapters that could handle a varying number of colors.
When IBM introduced the Video Graphics Array (VGA) in 1987, a new graphics standard came into being. A VGA display could support up to 256 colors (out of a possible 262,144-color palette) at resolutions up to 720x400. Perhaps the most interesting difference between VGA and the preceding formats is that VGA was analog, whereas displays had been digital up to that point. Going from digital to analog may seem like a step backward, but it actually provided the ability to vary the signal for more possible combinations than the strict on/off nature of digital. Of course, the way we manipulate digital display data has changed significantly since the days of CGA and EGA. Now, graphics-card manufacturers are able to provide all-digital display solutions that can support the same number of colors that analog adapters can.
Over the years, VGA gave way to Super Video Graphics Array (SVGA). SVGA cards were based on VGA, but each card manufacturer added resolutions and increased color depth in different ways. Eventually, the Video Electronics Standards Association (VESA) agreed on a standard implementation of SVGA that provided up to 16.8 million colors and 1280x1024 resolution. Most graphics cards available today support Ultra Extended Graphics Array (UXGA). UXGA can support a palette of up to 16.8 million colors and resolutions up to 1600x1200 pixels.
Graphics cards adhere to industry standards so that you can choose from a variety of cards for your PC. Even though any card you can buy today will offer higher colors and resolution than the basic VGA specification, VGA mode is the de facto standard for graphics and is the minimum on all cards. In addition to including VGA, a graphics card must be able to connect to your computer. While there are still a number of graphics cards that plug into an Industry Standard Architecture (ISA) or Peripheral Component Interconnect (PCI) slot, most current graphics cards use the Accelerated Graphics Port (AGP).
What's a Graphics Card?
A modern graphics card is a circuit board with memory and a dedicated processor. The processor is designed specifically to handle the intense computational requirements of displaying graphics. Most of these graphics processors have special command sets for graphics manipulation built right into the chip.
Graphics cards are known by many names, such as:
• Video cards
• Video boards
• Video display boards
• Graphics boards
• Graphics adapter cards
• Video adapter cards
Today's graphics cards are computing systems in their own right. But these cards started out as very simple devices. By understanding the evolution of graphics cards, you can begin to see why they are so powerful today.
Graphics Card Basics
You can better understand the essence of a graphics card by looking at the simplest possible one. This card would be able to display only black or white pixels, and it would do that on a 640x480-pixel screen.
Here are the three basic components of a graphics card and what they do:
• Memory - The first thing that a graphics card needs is memory. 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 (See How Bits and Bytes Work for details.). 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) 38,400 bytes of memory to hold all of the pixels visible on the display.
• 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.
• 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 (see How Television Works for details). 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.