A video card, also known as a graphics accelerator card, display adapter, or graphics card, is an expansion card whose function is to generate and output images to a display. Some video cards offer added functions, such as video capture, TV tuner adapter, MPEG-2 and MPEG-4 decoding, FireWire, light pen, TV output, or the ability to connect multiple monitors.

A misconception regarding high end video cards is that they are strictly used for video games. High end video cards have a much broader range of capability; for example, they play a very important role for graphic designers and 3D animators, who tend to require optimum displays as well as faster rendering.

Video cards are not used exclusively in IBM type PCs; they have been used in devices such as Commodore Amiga (connected by the slots Zorro II and Zorro III), Apple II, Apple Macintosh, Atari Mega ST/TT (attached to the MegaBus or VME interface), Spectravideo SVI-328, MSX, and in video game consoles.

Video hardware can be integrated on the mainboard, as it often happened with early computers; in this configuration it was sometimes referred to as a video controller or graphics controller.

Components

A modern video card consists of a printed circuit board on which the components are mounted. These include:

 

Graphics processing unit (GPU)

A GPU is a dedicated processor optimized for accelerating graphics. The processor is designed specifically to perform floating-point calculations which are fundamental to 3D graphics rendering. The main attributes of the GPU are the core clock frequency, which typically ranges from 250 to 850 MHz, and the number of pipelines (vertex and fragment shaders), which translate a 3D image characterized by vertices and lines into a 2D image formed by pixels.

 

Video BIOS

The video BIOS or firmware contains the basic program that governs the video card's operations and provides the instructions that allow the computer and software to interact with the card. It may contain information on the memory timing, operating speeds and voltages of the graphics processor and RAM and other information. It is sometimes possible to change the BIOS (e.g. to enable factory-locked settings for higher performance) although this is typically only done by video card overclockers, and has the potential to irreversibly damage the card.

 

t]Video memory

Type	Memory clock rate (MHz)	Bandwidth (GB/s)
DDR	166 - 950	1.2 - 30.4
DDR2	533 - 1000	8.5 - 16
GDDR3	700 - 1800	5.6 - 54.4
GDDR4	1600 - 2400	64 - 156.6
GDDR5	3000 - 3800	130 - 230

The memory capacity of most modern video cards range from 128 MB to 4.0 GB, though very few cards actually go over 1.0 GB.. Since video memory needs to be accessed by the GPU and the display circuitry, it often uses special high speed or multi-port memory, such as VRAM, WRAM, SGRAM, etc. Around 2003, the video memory was typically based on DDRtechnology. During and after that year, manufacturers moved towards DDR2, GDDR3 and GDDR4 even GDDR5 utilized most notably by the ATI Radeon HD 4870. The effective memory clock rate in modern cards are generally between 400 MHz and 3.8 GHz.

Video memory may be used for storing other data as well as the screen image, such as the Z-buffer, which manages the depth coordinates in 3D graphics, textures, vertex buffers, and compiled shader programs.

RAMDAC

The RAMDAC, or Random Access Memory Digital-to-Analog Converter, converts digital signals to analog signals for use by a computer display that uses analog inputs such as CRT displays. Depending on the number of bits used and the RAMDAC data transfer rate, the converter will be able to support different computer display refresh rates. With CRT displays, it is best to work over 75 Hz and never under 60 Hz, in order to minimize flicker. (With LCD displays, flicker is not a problem.) Due to the growing popularity of digital computer displays and the integration of the RAMDAC onto the GPU die, it has mostly disappeared as a discrete component. All current LCD and plasma displays and TVs work in the digital domain and do not require a RAMDAC. There are few remaining legacy LCD and plasma displays which feature analog inputs (VGA, component, SCART etc.) only; these require a RAMDAC but they reconvert the analog signal back to digital before they can display it, with the unavoidable loss of quality stemming from this digital-to-analog-to-digital conversion.