A
video card,
video adapter,
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 and
2D graphics, video capture, TV-tuner
adapter, MPEG-2 and MPEG-4 decoding, FireWire, light pen, TV
output, or the ability to connect multiple monitors, while other
modern high performance cards are used for more graphically
demanding purposes such as PC games.
Video hardware can be integrated on the motherboard, as it often
happened with early computers; in this configuration it was
sometimes referred to as a
video controller or
graphics controller.
History
|
Year |
Text Mode
(columns/lines) |
Graphics Mode
(resolution/colors) |
Memory |
| MDA |
1981 |
80×25 |
- |
4 KB |
| CGA |
1981 |
80×25 |
640×200 / 4 |
16 KB |
| HGC |
1982 |
80×25 |
720×348 / 2 |
64 KB |
| PGA |
1984 |
80×25 |
640×480 / 256 |
320 KB |
| EGA |
1984 |
80×25 |
640×350 / 16 |
256 KB |
| 8514 |
1987 |
80×25 |
1024×768 / 256 |
- |
| MCGA |
1987 |
80×25 |
320×200 / 256 |
- |
| VGA |
1987 |
80×25 |
640×480 / 16 |
256 KB |
SVGA
(VBE 1.x) |
1989 |
80×25 |
800×600 / 256 |
512 KB |
| 640×480+ / 256+ |
512 KB+ |
| XGA |
1990 |
80×25 |
1024×768 / 256 |
1 MB |
| XGA-2 |
1992 |
80×25 |
1024×768 / 65,536 |
2 MB |
SVGA
(VBE 3.0) |
1998 |
132×60 |
1280×1024 / 16.7M |
- |
The first IBM PC video card, which was released with the first
IBM PC, was developed by
IBM in 1981. The
MDA (
Monochrome Display
Adapter) could only work in text mode representing 80 columns
and 25 lines (80x25) in the screen. It had a 4KB video memory and
just one color.
Starting with the MDA in 1981, several video cards were released,
which are summarized in the attached table.
VGA was widely accepted, which led some
corporations such as ATI
, Cirrus Logic and S3
to work with that video card, improving its resolution and the
number of colours it used. This developed into the
SVGA (
Super VGA)
standard, which reached 2 MB of video memory and a resolution of
1024x768 at
256 color mode.
In 1995 the first consumer 2D/3D cards were released, developed by
Matrox,
Creative, S3, ATI and others. These
video cards followed the SVGA standard, but incorporated 3D
functions. In 1997,
3dfx released the
Voodoo graphics chip, which was more powerful
compared to other consumer graphics cards, introducing 3D effects
such as
mip mapping,
Z-buffering and
anti-aliasing into the consumer market.
After this
card, a series of 3D video cards were released, such as
Voodoo2 from 3dfx, TNT and
TNT2 from NVIDIA
. The
bandwidth required by these cards was approaching the limits of the
PCI bus capacity.
Intel
developed
the AGP (Accelerated
Graphics Port) which solved the bottleneck between the
microprocessor and the video card. From 1999 until 2002,
NVIDIA controlled the video card market (taking over 3dfx) with the
GeForce family. The improvements carried out
at this time were focused in 3D algorithms and graphics processor
clock rate. Video memory was also increased to improve their data
rate;
DDR technology was
incorporated, improving the capacity of video memory from 32 MB
with GeForce to 128 MB with
GeForce
4.
From 2002
onwards, the video card market came to be dominated almost entirely
by the competition between ATI
and Nvidia
, with their
Radeon and Geforce
lines respectively, taking around 90% of the independent graphics
card market between them, while other manufacturers were forced
into much smaller, niche markets.
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 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.
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, 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,
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. 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 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.
Outputs
The most common connection systems between the video card and the
computer display are:
Video Graphics Array (VGA) (DE-15)
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 (
LCD, 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.
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).
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.
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 a 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 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. 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.
See also
References
- ATI FireGL V8650.
- NVIDIA Quadro FX 5800.
- http://www.xbitlabs.com/articles/video/display/power-noise.html
X-bit labs: Faster, Quieter, Lower: Power Consumption and Noise
Level of Contemporary Graphics Cards
- http://www.codinghorror.com/blog/archives/000662.html Coding
Horror Video Card Power Consumption
- Mueller, Scott (2005) Upgrading and Repairing PCs.
16th edition. Que Publishing. ISBN 0-7897-3173-8
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