©1998-2010 Griff Wason | All rights reserved. All trademarks and trade names acknowledged.

Comments:

This commission was undertaken for Popular Mechanics Magazine. It was one of a number of illustrations used to describe various crucial parts of a personal computer - the artwork shown is not in the form finally used in the magazine articles.

 

Description:

A video card, also known as a graphics accelerator card, display adapter, or graphics card, is a hardware component whose function is to generate and output images to a display. It operates on similar principles as a sound card or other peripheral devices.

 

The term is usually used to refer to a separate, dedicated expansion card that is plugged into a slot on the computer's motherboard, as opposed to a graphics controller integrated into the motherboard chipset. An integrated graphics controller may be referred to as an "integrated graphics processor" (IGP).

 

Some video cards offer added functions, such as video capture, TV tuner adapter, MPEG-2 and MPEG-4 decoding, FireWire, mouse, light pen, and joystick connectors, or even the ability to connect multiple monitors.

 

A common misconception regarding video cards is that they are strictly used for video games; a misconception that companies take advantage of in order to sell their products by advertising their products as if they were in fact video consoles. Video cards instead have a much broader range of capability. Being specialized for video, output video cards improve what a computer monitor displays. As well, they play a very important role for graphic designers and 3D animators, who tend to require optimum displays for their work as well as faster rendering in order to efficiently tone up their work.

 

Component parts

Most video cards consist of a printed circuit board on which the components are mounted. These include:

 

Graphics processing unit (GPU)

A GPU is a dedicated graphics microprocessor optimized for floating point calculations which are fundamental to 3D graphics rendering. The main attributes of the GPU are the core clock rate, which typically ranges from 250 MHz 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 interface 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.

 

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

 

If the video card is integrated in the motherboard, it may use the computer RAM (lower throughput). If it is not integrated, the video card will have its own video memory, called Video RAM. The memory capacity of most modern video cards range from 64MB to 4.0 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 DDR technology. During and after that year, manufacturers moved towards DDR2, GDDR3 and GDDR4 even GDDR5 utilized most notably by the ATI Radeon HD 4870. The 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.[9] (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.

 

Outputs

The most common connection systems between the video card and the computer display are:

 

Video Graphics Array (VGA) (DB-15 connector)

Analog-based standard adopted in the late 1980s designed for CRT displays, also called VGA connector. Some problems of this standard are electrical noise, image distortion and sampling error evaluating pixels.

 

Digital Visual Interface (DVI)

Digital-based standard designed for displays such as flat-panel displays (LCDs, plasma screens, wide High-definition television displays) and video projectors. It avoids image distortion and electrical noise, corresponding each pixel from the computer to a display pixel, using its native resolution.

 

Video In Video Out (VIVO) for S-Video, Composite video and Component video

Included to allow the connection with televisions, DVD players, video recorders and video game consoles. They often come in two 9-pin Mini-DIN connector variations, and the VIVO splitter cable generally comes with either 4 connectors (S-Video in and out + composite video in and out) or 6 connectors (S-Video in and out + component PB out + component PR out + component Y out (also composite out) + composite in).

PCI Video card and cage