Video Card
From HTPCnz
Contents |
Definition
A video card, also referred to as a graphics accelerator card, display adapter, graphics card, and numerous other terms, is an item of personal computer hardware 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 functionalities, such as video capture, TV tuner adapter, MPEG-2 and MPEG-4 decoding or even FireWire, mouse, light pen, joystick connectors, or even the ability to connect two monitors.
Video cards are not used exclusively in IBM type PCs; they have been used in devices such as Commodore Amiga (connected by the slots Zorro II and Zorro III), Apple II, Apple Macintosh, Atari Mega ST/TT (attached to the MegaBus or VME interface), Spectravideo SVI-328, MSX and in video game consoles.
Components
A 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 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 1200 MHz in modern cards, 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.
| Type | 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 |
Video memory
If the video card is integrated in the motherboard, it will use the computer RAM memory (lower throughput). If it is not integrated, the video card will have its own video memory which is called Video RAM or VRAM. The VRAM capacity of most modern video cards range from 128 to 1024 MB (workstation graphics cards). Before 2003, the VRAM was typically based on DDR technology. During and after that year, manufacturers moved towards the vastly superior DDR2, GDDR3 and GDDR4. The memory clock rate is between 400 MHz and 1.6 GHz. A very important element of the video memory is the Z-buffer, which manages the depth coordinates in 3D graphics.
Video BIOS
The video BIOS or firmware chip is a chip that 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 contains information on the memory timing, operating speeds and voltages of the processor and ram and other information. It is possible to re-flash a BIOS (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.
RAMDAC
Random Access Memory Digital-to-Analog Converter. RAMDAC takes responsibility for turning the digital signals produced by the computer processor into an analog signal which can be understood by the computer display. 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 minimise flicker. Due to the growing popularity of digital computer displays and the migration of some of its functions to the motherboard, the RAMDAC is slowly disappearing. 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 do 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
- SVGA: Analog-based standard adopted in the late 1980s designed for CRT displays. Some problems of this standard are electrical noise, image distortion and sampling error evaluating pixels.
- DVI: Digital-based standard designed for displays such as LCDs, plasma screens and video projectors. It avoids image distortion and electrical noise, corresponding each pixel from the computer to a display pixel, using its native resolution.
- S-Video: Included to allow the connection with DVD players, video recorders and video game consoles.
Other connection systems are:
- Composite video: Analogic system, with very low resolution. It uses RCA connector.
- Component video: It has three cables, each with RCA connector (YCbCr); it is used in projectors.
- HDMI: digital technology released in 2003, whose goal is to replace all the others.
| 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 | 133 | 528 | Parallel |
| AGP 4x | 32 | 266 | 1000 | Parallel |
| AGP 8x | 32 | 533 | 2000 | Parallel |
| PCIe x1 | 1*32 | 25 / 50 | 100 / 200 | Serial |
| PCIe x4 | 1*32 | 25 / 50 | 400 / 800 | Serial |
| PCIe x8 | 1*32 | 25 / 50 | 800 / 1600 | Serial |
| PCIe x16 | 1*32 | 25 / 50 | 1600 / 3200 | Serial |
Motherboard interface
Chronologically, connection systems between video card and motherboard were, mainly:
- ISA: 16 bits architecture, 8 MHz data transfer rate. Released in 1981 by IBM, dominant in the marketplace in the 1980s.
- MCA: 32 bits, 10 MHz. Released in 1987 by IBM. It wasn’t compatible with previous motherboards.
- EISA: 32 bits, 8.33 MHz. Released in 1988 to compete with IBM. Compatible with previous motherboards.
- VESA: ISA extension. 32 bit, 33 MHz.
- PCI: 32 bit, 33 MHz. Replaced the previous buses from 1993. PCI allowed dynamic connectivity between devices, avoiding the jumpers manual adjustments. PCI-X was a version that improved PCI to 64 bits and 133 MHz.
- AGP: Dedicated to graphics bus, 32 bits, 66 MHz.
- PCI-Express: Point to point interface, released in 2004. In 2006 provided double data transfer rate of AGP. 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.
Cooling devices
Due to video card work charge, high temperatures are reached, which can cause a breakdown. Cooling devices are incorporated to avoid excessive heat. There are two types of cooling devices, and both can be used at the same time:
- Heat sink: generally referred to as a passive cooling device, it has no moving parts and, therefore, is soundless and very reliable; it absorbs and dissipates heat from the GPU using thermal contact (by either direct or radiant contact with a cooling medium such as air). Its effectiveness depends on its size and other characteristics including shape and material (generally copper or aluminium).
- Computer fan: usually known as an active cooling device, it has moving parts to push hot air away from the video card and as such will generate a small amount of noise. It is more effective than a heat sink at cooling, but due to the moving parts is far less reliable than a passive heat-sink.
- Water Block (See: liquid cooling): uses liquid and heat sinks to cool the GPU. This method is used less often but is much more favorable to both other options as it is more effective than a fan and soundless just like a passive cooling device.
Power supply
Until 2006, video card power consumption had not been a big problem; nevertheless, present video card tendency is to consume even more power. Although power supplies are increasing their power too, the bottleneck is due to the PCI-Express connection, which is limited to supplying 150W. Nowadays, video cards with a power consumption over 150W usually include a six-pin power socket that connects directly to the power supply, which allows a direct connection between the computer power supply and the card, avoiding motherboard connection and, therefore, the PCIe port.
Graphics APIs
Due to the difficulties working with video cards at a programming level, interfaces which abstract the complexity and diversity of the graphic card primitives appeared. The most important are:
- Direct3D: Released by Microsoft in 1996, is a component of DirectX. Designed to be used exclusively in Windows, it is used by the majority of Windows videogames. The latest version of DirectX is DirectX 10, although the majority of computers still rely on graphics cards that use DirectX 9.0c.
- OpenGL: Developed by Silicon Graphics in the early 1990s, OpenGL is a free, open, multi-language and multi-platform API. It is widely used in CAD, virtual reality, scientific visualization, information visualization, flight simulation and some games, particularly on Linux and other Unix like operating systems. The latest version is OpenGL 2.1.
Graphics techniques
Some of the most frequently used effects for enhancing the perceived quality of the output of graphics cards include the following:
- Anti-aliasing (AA): a technique used to counter distortion caused by aliasing effects.
- Shader: pixel and vertex processing in terms of illumination, atmospheric optical phenomena or multi-layer surfaces.
- High dynamic range rendering (HDR): a technique used to enable a wider range of brightness in real scenes (from light sources to dark shadows).
- Texture mapping: allows the addition of details on surfaces, without adding complexity.
- Motion blur: technique that blurs objects in motion.
- Depth of field: technique that blurs out of focus objects.
- Lens flare: imitation of light sources.
- Fresnel effect: reflections over an object, depending on the angle of vision. The more angle of vision, the more reflection.
- Anisotropic filtering: enhances viewing angle of a displayed texture as it increases.
HTPC Requirements
GPU
The processing power of the GPU was the first consideration for selecting the video card, but with the introduction of FreeviewHD, the terrestial mode of Freeview, hardware decoding of the MPEG4/H.264 is now an important consderation. Native hardware decoding by the graphics card means considerably less work for the CPU. Yet, the processing power of the most recent models on the market have even excessive power compared to the Media Center requirements. These newer cards are designed for 3D Gaming requirements, which are significantly higher and the cards are on the edge of meeting these requirements.
nVidia vs. ATI
There are two main video chip manufacturers - nVidia and ATI. Both have adequate configurations, so the main differentiation point becomes stability of the drivers and general other issues with the cards.
Cooling
Silent operation is a prerequisite for the Media Center. Given the high load on the GPU, they typically require a dedicated cooling. There are models with passive cooling (ie a large heatsink rather than a smaller heatsink with a fan) that we recommend for that purpose. Please also check whether the model of your choice will require additional space from the neighboring PCI slot, something you usually want to avoid. There are good models on the market which fit into one PCI-E X16 slot. Another thing to consider is that the heatpipes connecting the radiator on the opposite side to the chip goes over the card and requires additional space. You need to make sure it will let you close the cover of your media center case.
MCE compatible cards
ASUSTeK Computer Inc.
- ASUS X700, X800, EN6600, EN6800 SERIES
ATI Technologies
- IncMOBILITY RADEON 9800, X700, X800
- IncRADEON 9800, X600 XT, X700, X800, X850 Series
NVIDIA Corporation
- GeForce FX 5200, FX 5700, FX 5750, FX 5900, 6200 Turbo Cache, 6600, 6800, Go 6800
S3 Graphics, Inc.
- S3 Graphics GammaChrome
Extremetech recently did a review of ATI vs. nVidia for video viewing and the newer ATI cards came out on top.
Power Consumption:
http://www.xbitlabs.com/articles/video/display/gpu-consumption2006_8.html http://www.xbitlabs.com/articles/video/display/ati-vs-nv-power_10.html http://www.xbitlabs.com/articles/video/display/gpu-consumption2006_5.html
HDCP complient cards
comprehensive list at www.hardforum.com/showthread.php?t=1071342 www.htpcnews.com/forums/index.php?act=ST&f=7&t=23416
Brands
- AMD
- Asus
- ATI
- Chaintech
- Gigabyte
- Intel
- Matrox
- MSI
- NVIDIA
- S3 Graphics
- Sparkle
- VIA Technologies
- XFX
- XGI Tech
- Xpertvision
