A video card, video adapter or a graphics accelerator card, display adapter, or graphics card, is an expansion card whose function is to generate and output images to a display. Many video cards offer added functions, such as accelerated rendering of 3D scenes, video capture, TV tuner adapter, MPEG-2 and MPEG-4 decoding, FireWire, light pen, TV output, or the ability to connect multiple monitors.
Video hardware can be integrated on the motherboard, as was common 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.
Video memory
The memory capacity of most modern video cards ranges from 128 MB to 4 GB, though very few cards actually go over 1 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 effective memory clock rate in modern cards is generally between 400 MHz and 3.8 GHz.
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.
Outputs
The most common connection systems between the video card and the computer display are:
Video Graphics Array (VGA): Analogue-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).
High-Definition Multimedia Interface (HDMI): An advanced digital audio/video interconnect released in 2003, and is commonly used to connect game consoles and DVD players to a display. HDMI supports copy protection through HDCP.
DisplayPort: An advanced license and royalty-free digital audio/video interconnect released in 2007. DisplayPort intends to replace VGA and DVI for connecting a display to a computer.
Cooling devices
Video cards may use a lot of electricity, which is converted into heat. If the heat isn’t dissipated, the video card could overheat and be damaged. Cooling devices are incorporated to transfer the heat elsewhere. Three types of cooling devices are commonly used on video cards:
• Heat sink: a heat sink is a passive cooling device. It conducts heat away from the graphics card’s core, or memory, by using a heat conductive metal, most commonly aluminum or copper, sometimes in combination with heat pipes. It uses air (most common) or in extreme cooling situations, water (see water block), to remove the heat from the card. When air is used, a fan is often used to increase cooling effectiveness.
• Computer fan: an example of an active cooling part. It is usually used with a heatsink. Due to the moving parts, a fan requires maintenance and possible replacement. The fan speed or actual fan can be changed for more efficient or quieter cooling.
• Water block: A water block is a heat sink suited to use water instead of air. It is mounted on the graphics processor and has a hollow inside. Water is pumped through the water block, transferring the heat into the water, which is then usually cooled in a radiator. This is the most effective cooling solution without extreme modification.
Power demand
As the processing power of video cards has increased, so has their demand for electrical power. Present fast video cards tend to consume a great deal of power. While CPU and power supply makers have recently moved toward higher efficiency, power demands of GPUs have continued to rise, so the video card may be the biggest electricity user in a computer. Although power supplies are increasing their power too, the bottleneck is due to the PCI-Express connection, which is limited to supplying 75 W. Nowadays, video cards with a power consumption over 75 watts usually include a combination of six pin (75W) or eight pin (150W) sockets that connect directly to the power supply to supplement power.
Manufacturers
• ATI
• Evga
• Leadtek
• Matrox
• MSI
• Nvidia
• Sapphire
• XFX