What Is a Graphics Card?

Also referred to as a video card or video accelerator, a graphics card is a form of display adapter. The display adapter is the component of a computer that processes all information sent to the video output device - usually the monitor.

The viewing surface of a monitor is comprised of thousands of tiny dots, called pixels. These pixels are activated, deactivated, and assigned color by the display adapter, based on the needs of the software running on the computer.

Every change that takes place on the screen - whether it's a mouse movement or a movie - is communicated from the software producing the image to the monitor via the display adapter.

The rate at which the image on the monitor changes is known as the refresh rate. This rate is generally expressed in Hertz - therefore a Hertz frequency of 75 means that the display adapter sends a new viewable image to the monitor 75 times per second.

Display adapters vary greatly in power, versatility, and cost, and are chosen based on the intended purpose of the host computer. A terminal that will be used for simple data entry can get by with a rudimentary display adapter, while a workstation used to produce CGI special effects for movies requires massive video processing power.

Components of a Graphics Card

Most graphics cards manufactured today include an on-board Graphics Processing Unit, or GPU, which handles advanced on-board graphics processing and rendering. The GPU is the central and most important feature of the graphics card, since the speed of the GPU dictates the speed at which all the graphical functions operate.

Another important part of a graphics card is the available memory that the card can use to store and send images to the monitor. This memory is expressed in megabytes or gigabytes of RAM. A "512 meg" graphics card is understood to have 512 Megabytes of RAM, while a "2 gig" card has 2 Gigabytes of RAM.

Along with memory, a graphics card contains several crucial elements:

The input/output chip, or BIOS chip, stores the firmware and diagnostic tools hard-coded on the card. When the computer boots up, this chip tells the computer what kind of card it is and what kind of software it can use.

The Digital-to-Analog Converter, or RAMDAC, translates images stored in the RAM into a format the monitor understands, and feeds them to the output port.

The Output Port physically connects the graphics card to a monitor. There are many different kinds of output ports, ranging from standard VGA to the more intricate HDMI.

The Physical Motherboard Connection generally takes place at the bottom of the card, where the exposed circuits of the Graphics card can sync up with a connection slot in the host motherboard.

Three-Dimensional Output

Part of the reason high end graphics programs require large amount of video horsepower has to do with the way images are created in the computer before being displayed on the monitor.

Some software, like games or the programs used to create CGI special effects for movies, require real-time computation of three-dimensional figures before the image can be sent to the monitor. This is known as 3D rendering.

3D images are comprised of a series of triangles, or polygons, that represent three dimensional objects moving in real space. Rendering requires that these polygons move in a realistic way, that they be painted with specific textures, and that the effects of reflecting light sources be represented along their surface.

And all of this has to be calculated in real time, many times per second. Obviously, 3D rendering is far more demanding than a word processing program, and therefore the horsepower of high end graphics cards is the key factor in determining the quality of the images displayed on the monitor.

Frame Rate

Frame Rate is the expression of how many times the graphics card is able to calculate all of the factors above, produce a new image, and send it to the monitor. The human eye sees at approximately 30 frames per second, but any rendering that takes place at less than 60 frames per second will appear to chop or flicker to most people.

Thus, frame rate is most often used as the overall performance indicator of a graphics card. Given a specified set of polygons, textures, and light sources, if graphics card A is able to render a greater number of frames-per-second than graphics card B, graphics card A is said to be "faster" than graphics card B.

Since speed is of the essence in most 3D applications, the faster the card, the more sought - and expensive - it tends to be.