A
video card,
video adapter,
graphics accelerator card,
display adapter, or
graphics card is an
expansion card whose function is to generate output images to a display. Many video cards offer added
functions, such as accelerated rendering of 3D scenes and 2D graphics, video capture, TV-tuner adapter, MPEG-2/MPEG-4 decoding, FireWire, light pen, TV output, or the ability to connect multiple monitors (multi-monitor). Other modern high performance video cards are used for more graphically demanding purposes, such as PC games.
Video hardware can be integrated on the
motherboard, often occurring with early machines. In this configuration it is sometimes referred to as a
video controller or
graphics controller. Modern low-end to mid-range motherboards often include a graphics chipset developed by the developer of the
northbridge (i.e. an
nForce chipset with
nVidia graphics or an
Intel chipset with Intel graphics) on the motherboard. This graphics chip usually has a small quantity of embedded memory and takes some of the system's main RAM, reducing the total RAM available. This is usually called
integrated graphics or
on-board graphics, and is low-performance and undesirable for those wishing to run 3D applications. A dedicated Graphics Card on the other hand has its own RAM and Processor specifically for processing video images, and thus offloads this work from the CPU and system RAM. Almost all of these motherboards allow the disabling of the integrated graphics chip in
BIOS, and have an
AGP,
PCI, or
PCI Express slot for adding a higher-performance graphics card in place of the integrated graphics. Despite the performance limitations, around 95% of new computers are sold with integrated graphics processors, leaving it for the individual user to decide whether to install a dedicated Graphics card.
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-pointcalculations, which are fundamental to 3D graphics rendering. The main attributes of the GPU are the core
clock frequency, which typically ranges from 250 MHz to 4 GHz 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.
Modern GPUs are massively parallel, and fully programmable. Their computing power is orders of magnitude higher than that of CPUs. As consequence, they challenge CPU in high performance computing, leading manufacturers like Intel and AMD to integrate video, or massive parallelism, on processors.
=== Video BIOS ===
The
video BIOS or
firmware contains the basic program, which is usually hidden, 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, 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 - 2400 | 5.6 - 156.6 |
| GDDR4 | 2000 - 3600 | 128 - 200 |
| GDDR5 | 3400 - 5600 | 130 - 230 |
The memory capacity of most modern video cards ranges from 128 MB to 4 GB.
[1][2] 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,
GDDR4, and 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.
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. The RAMDAC is a kind of RAM chip that regulates the functioning of the graphics card. 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.
[3] (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 LCDs, plasma displays and TVs work in the digital domain and do not require a RAMDAC. There are few remaining legacy LCD and plasma displays that 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.
The most common connection systems between the video card and the computer display are:
Video Graphics Array (VGA) (DE-15)
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. In some rare cases high end CRT monitors also use DVI. It avoids image distortion and electrical noise, corresponding each pixel from the computer to a display pixel, using its
native resolution. It is worth to note that most manufacturers include DVI-
I connector, allowing(via simple adapter) standard RGB signal output to an old CRT or LCD monitor with VGA input.
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 P
B out + component P
R out + component Y out [also composite out] + composite in).
High-Definition Multimedia Interface (HDMI)
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.
Other types of connection systems
Motherboard interface
Chronologically, connection systems between video card and motherboard were, mainly:
- S-100 bus: designed in 1974 as a part of the Altair 8800, it was the first industry-standard bus for the microcomputer industry.
- ISA: Introduced in 1981 by IBM, it became dominant in the marketplace in the 1980s. It was an 8 or 16-bit bus clocked at 8 MHz.
- NuBus: Used in Macintosh II, it was a 32-bit bus with an average bandwidth of 10 to 20 MB/s.
- MCA: Introduced in 1987 by IBM it was a 32-bit bus clocked at 10 MHz.
- EISA: Released in 1988 to compete with IBM's MCA, it was compatible with the earlier ISA bus. It was a 32-bit bus clocked at 8.33 MHz.
- VLB: An extension of ISA, it was a 32-bit bus clocked at 33 MHz.
- PCI: Replaced the EISA, ISA, MCA and VESA buses from 1993 onwards. PCI allowed dynamic connectivity between devices, avoiding the jumpers manual adjustments. It is a 32-bit bus clocked 33 MHz.
- UPA: An interconnect bus architecture introduced by Sun Microsystems in 1995. It had a 64-bit bus clocked at 67 or 83 MHz.
- USB: Mostly used for other types of devices, but there are USB displays.
- AGP: First used in 1997, it is a dedicated-to-graphics bus. It is a 32-bit bus clocked at 66 MHz.
- PCI-X: An extension of the PCI bus, it was introduced in 1998. It improves upon PCI by extending the width of bus to 64-bit and the clock frequency to up to 133 MHz.
- PCI Express: Abbreviated PCIe, it is a point to point interface released in 2004. In 2006 provided double the data-transfer rate of AGP. It should not be confused with PCI-X, an enhanced version of the original PCI specification.
In the attached table
[4] is a comparison between a selection of the features of some of those interfaces.
| Bus | Width (bits) | Clock rate (MHz) | Bandwidth (MB/s) | Style |
|---|
| ISA XT | 8 | 4,77 | 8 | Parallel |
| ISA AT | 16 | 8,33 | 16 | Parallel |
| MCA | 32 | 10 | 20 | Parallel |
| EISA | 32 | 8,33 | 32 | Parallel |
| VESA | 32 | 40 | 160 | Parallel |
| PCI | 32 - 64 | 33 - 100 | 132 - 800 | Parallel |
| AGP 1x | 32 | 66 | 264 | Parallel |
| AGP 2x | 32 | 66 | 528 | Parallel |
| AGP 4x | 32 | 66 | 1000 | Parallel |
| AGP 8x | 32 | 66 | 2000 | Parallel |
| PCIe x1 | 1 | 2500 / 5000 | 250 / 500 | Serial |
| PCIe x4 | 1 × 4 | 2500 / 5000 | 1000 / 2000 | Serial |
| PCIe x8 | 1 × 8 | 2500 / 5000 | 2000 / 4000 | Serial |
| PCIe x16 | 1 × 16 | 2500 / 5000 | 4000 / 8000 | Serial |
| PCIe x16 2.0 | 1 × 16 | 5000 / 10000 | 8000 / 16000 | Serial |
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 heat sink. 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.
[5][6] Although power supplies are increasing their power too, the
bottleneck is due to the
PCI-Express connection, which is limited to supplying 75 Watts.
[7] 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
