A video card (also called a video adapter, display card, graphics card, graphics board, display adapter or graphics adapter and sometimes preceded by the word discrete or dedicated to emphasize the distinction between this implementation and integrated graphics) is an expansion card which generates a feed of output images to a display (such as a computer monitor). Within the industry, video cards are sometimes called graphics add-in-boards, abbreviated as AIBs, with the word "graphics" usually omitted. Virtually all current video cards are built with either AMD-sourced or Nvidia-sourced graphics chips. Most video cards offer various functions such as accelerated rendering of 3D scenes and 2D graphics, MPEG-2/MPEG-4 decoding, TV output, or the ability to connect multiple monitors (multi-monitor).
Dedicated vs integrated graphics
As an alternative to the use of a video card, video hardware can be integrated into the motherboard or the CPU. Both approaches can be called integrated graphics. Motherboard-based implementations are sometimes called "on-board video" while CPU-based implementations are called accelerated processing units or APUs. Almost all motherboards with integrated graphics allow the disabling of the integrated graphics chip in BIOS, and have a PCI, or PCI Express(PCI-E) slot for adding a higher-performance graphics card in place of the integrated graphics. The ability to disable the integrated graphics sometimes also allows the continued use of a motherboard on which the on-board video has failed. Sometimes both the integrated graphics and a dedicated graphics card can be used simultaneously to feed separate displays. The main advantages of integrated graphics include cost, compactness, simplicity and low energy consumption. The performance disadvantage of integrated graphics arises because the graphics processor shares system resources with the CPU. A dedicated graphics card has its own random access memory (RAM), its own cooling system, and dedicated power regulators, with all components designed specifically for processing video images. Upgrading to a dedicated graphics card offloads work from the CPU and system RAM, so not only will graphics processing be faster, but the computer's overall performance may also improve.
Both of the dominant CPU makers, AMD and Intel, are moving to APUs. One of the reasons is that graphics processors are powerful parallel processors, and placing them on the CPU die allows their parallel processing ability to be harnessed for various computing tasks in addition to graphics processing. (See Heterogeneous System Architecture, which discusses AMD's implementation.) APUs are the newer integrated graphics technology and, as costs decline, will probably be used instead of integrated graphics on the motherboard in most future low and mid-priced home and business computers. As of late 2013, the best APUs provide graphics processing equivalent to mid-range video cards and are adequate for casual gaming. Users seeking the highest video performance for gaming or other graphics-intensive uses should still choose computers with dedicated graphics cards.
As the processing power of video cards has increased, so has their demand for electrical power. Current high-performance video cards tend to consume a great deal of power. For example, the thermal design power (TDP) for the GeForce GTX TITAN is 250 Watts. 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 Watts. Modern 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. While manufacturers of high-end video cards may recommend a minimum power supply of 500 Watts in a computer, a power supply of at least 750 Watts is typical in a gaming computer with a single high end video card. Providing adequate cooling becomes a challenge in such computers. Computers with multiple video cards may need power supplies in the 1000W-1500W range. Heat extraction becomes a major design consideration for computers with two or more high end video cards.
Size
Video cards for desktop computers come in 2 size profiles, to allow adding a graphics card to even small form factor PCs. These sizes are regular and low-profile video cards. the profiles are based on width only, with low-profile card taking up less than the full width of a PCIe slot. The length and thickness vary greatly, high-end cards usually occupy 2 or 3 expansion slots, and vary greatly in length, with dual-gpu cards -such as the Nvidia GeForce GTX 690- generally over 10" in length.
Multi-card scaling
Some graphics cards can be linked together to allow scaling of the graphics processing across multiple cards. This is done using either the PCIe bus on the motherboard, or, more commonly, a data bridge. Generally, the cards must be of the same model to be linked, and most low power cards are not able to be linked in this way. AMD and Nvidia both have proprietary methods of scaling, CrossfireX for AMD, and SLI for Nvidia. Cards from different manufacturers and/or architectures cannot be used together for multi card scaling. Currently, scaling can be done using up to four cards.
Device drivers
The device driver usually supports one or multiple Application programming interfaces (APIs) like OpenGL, Direct3D, or Mantle, and the architecture of a GPU-family. A device driver has to be specifically written for an operating system.
