The images you see on your monitor are made of tiny dots called pixels. At most common resolution settings, a screen displays over a million pixels, and the computer has to decide what to do with every one in order to create an image. To do this, it needs a translator -- something to take binary data from the CPU and turn it into a picture you can see. Unless a computer has graphics capability built into the motherboard, that translation takes place on the graphics card.
Graphics Card Basics
 The four main components of a graphics card are connections for the motherboard and monitor, a processor, and memory. |
A graphics card works along the same principles. The CPU, working in conjunction with software applications, sends information about the image to the graphics card. The graphics card decides how to use the pixels on the screen to create the image. It then sends that information to the monitor through a cable.
Creating an image out of binary data is a demanding process. To make a 3-D image, the graphics card first creates a wire frame out of straight lines. Then, it rasterizes the image (fills in the remaining pixels). It also adds lighting, texture and color. For fast-paced games, the computer has to go through this process about sixty times per second. Without a graphics card to perform the necessary calculations, the workload would be too much for the computer to handle.
The graphics card accomplishes this task using four main components:
Like a motherboard, a graphics card is a printed circuit board that houses a processor and RAM. It also has an input/output system (BIOS) chip, which stores the card's settings and performs diagnostics on the memory, input and output at startup. A graphics card's processor, called a graphics processing unit (GPU), is similar to a computer's CPU. A GPU, however, is designed specifically for performing the complex mathematical and geometric calculations that are necessary for graphics rendering. Some of the fastest GPUs have more transistors than the average CPU. A GPU produces a lot of heat, so it is usually located under a heat sink or a fan.
 A heat sink or fan keeps a graphics card's processor from overheating. |
In addition to its processing power, a GPU uses special programming to help it analyze and use data. ATI and nVidia produce the vast majority of GPUs on the market, and both companies have developed their own enhancements for GPU performance. To improve image quality, the processors use:
Each company has also developed specific techniques to help the GPU apply colors, shading, textures and patterns.
As the GPU creates images, it needs somewhere to hold information and completed pictures. It uses the card's RAM for this purpose, storing data about each pixel, its color and its location on the screen. Part of the RAM can also act as a frame buffer, meaning that it holds completed images until it is time to display them. Typically, video RAM operates at very high speeds and is dual ported, meaning that the system can read from it and write to it at the same time.
The RAM connects directly to the digital-to-analog converter, called the DAC. This converter, also called the RAMDAC, translates the image into an analog signal that the monitor can use. Some cards have multiple RAMDACs, which can improve performance and support more than one monitor. The RAMDAC sends the final picture to the monitor through a cable.
To figure out what the memory requirements are, multiply the
width x height x (bit/8) / 1024 = KB / 1024 = MB of RAM needed.
Using a graphics card that is monochrome requires 1 bit per pixel, therefore it can be calculated that if a screen is 640 x 480 it would take 307k of memory to display it.
To display more colors, more bits are required. Common
numbers of colors are
2 colors/1 bit
4 colors/2 bits
16 colors/4 bits
256 colors/8 bits
64k colors/16 bits
16 million colors/24 bits
4 billion colors/32 bits
Connections to the motherboard are usually through one of three interfaces:
Most graphics cards have two monitor connections. Often, one is a DVI connector, which supports LCD screens, and the other is a VGA connector, which supports CRT screens. Some graphics cards have two DVI connectors instead. But that doesn't rule out using a CRT screen; CRT screens can connect to DVI ports through an adapter.
Most people use only one of their two monitor connections. People who need to use two monitors can purchase a graphics card with dual head capability, which splits the display between the two screens. A computer with two dual head, PCIe-enabled video cards could theoretically support four monitors.
 This Radeon X800XL graphics card has DVI, VGA and ViVo connections. |
In addition to connections for the motherboard and monitor, some graphics cards have connections for:
Display resolutions are based on the pixel width and height. As video displays became more advanced, the resolutions grew as well. The A+ certification test does require a little knowledge into the most common resolution types as listed.
MDA (Monochrome Display Adapter) – Displayed
two colors, text only, could display 80x25 characters
CGA (Color Graphics Adapter) – Displays 4
colors at 320x200 or 2 colors at 640x200
EGA (Enhanced Graphics Adapter) – Displays
16 colors at 640x350
VGA (Video Graphics Array) – Displays 16
colors at 640x480 or 256 colors at 320x200
SVGA (Super
Video Graphics Array) –
Displays up to 16 million colors at 1280x1024 (800x600 is standard)
XGA (eXtended Graphics Array) – Refers to
displays at 1024x768
SXGA (Super eXtended Graphics Array) –
Displays at 1280x1024
SXGA+ - Displays at 1400x1050
WSXGA – Displays at 1600x900 or 1600x1024
UXGA (Ultra extended graphics array) –
1600x1200
WUXGA – 1920x1200
WXGA (Wide extended graphics array) – 1366x768
| Computer Standard | Resolution | Display Aspect Ratio | Pixels |
|---|---|---|---|
| VIC-II multicolor, IBM PCjr 16-color | 160×200 | 4:5 | 32,000 |
| Acorn BBC 20 column modes | 160×256 | 5:8 | 40,960 |
| TMS9918, ZX Spectrum | 256×192 | 4:3 | 49,152 |
| Apple II HiRes | 280×192 | 35:24 | 53,760 |
| Atari 400/800 | 320×192 | 5:3 | 61,440 |
| CGA 4-color, Atari ST 16 color, VIC-II HiRes, Amiga OCS NTSC LowRes | 320×200 | 8:5 | 64,000 |
| QVGA | 320×240 | 4:3 | 76,800 |
| Acorn BBC 40 column modes | 320×256 | 5:4 | 76,800 |
| Amiga OCS PAL LowRes | 320×256 | 5:4 | 76,800 |
| WQVGA | 432×240 | 9:5 | 103,680 |
| HVGA | 480×320 | 3:2 | 153,200 |
| Black & white Macintosh (9") | 512×342 | 3:2 | 175,104 |
| Macintosh LC (12")/Color Classic | 512×384 | 4:3 | 196,608 |
| Apple IIe Double HiRes | 560×192 | 35:12 | 107,520 |
| Atari ST 4 color, CGA mono, Amiga OCS NTSC HiRes | 640×200 | 16:5 | 128,000 |
| Acorn BBC 80 column modes | 640×256 | 5:2 | 163,840 |
| Amiga OCS PAL HiRes | 640×256 | 5:2 | 163,840 |
| EGA | 640×350 | 64:35 (approx. 9:5) | 224,000 |
| Atari ST mono, Amiga OCS NTSC interlaced | 640×400 | 8:5 | 256,000 |
| VGA and MCGA | 640×480 | 4:3 | 307,200 |
| Amiga OCS PAL interlaced | 640×512 | 5:4 | 327,680 |
| HGC | 720×348 | 60:29 (approx. 2:1) | 250,560 |
| MDA | 720×350 | 72:35 (approx. 2:1) | 252,000 |
| Apple Lisa | 720×360 | 2:1 | 259,200 |
| WGA or WVGA | 800×480 | 5:3 | 384,000 |
| SVGA | 800×600 | 4:3 | 480,000 |
| Apple Macintosh | 832×624 | 4:3 | 519,168 |
| XGA | 1024×768 | 4:3 | 786,432 |
| NeXTcube | 1120×832 | 35:26 (approx. 4:3) | 931,840 |
| XGA+ | 1152×864 | 4:3 | 995,328 |
| Sun | 1152×900 | 32:25 (approx. 4:3) | 1,036,800 |
| WXGA | 1280×800 | 16:10 | 1,024,000 |
| Apple PowerBook G4 | 1280×854 | 640:427 (approx. 3:2) | 1,093,120 |
| SXGA alternative | 1280×960 | 4:3 | 1,228,800 |
| SXGA | 1280×1024 | 5:4 | 1,310,720 |
| WXGA | 1366×768 | 16:9 | 1,049,088 |
| WXGA+ | 1440×900 | 16:10 | 1,296,000 |
| SXGA+ | 1400×1050 | 4:3 | 1,470,000 |
| WSXGA | 1600×1024 | 25:16 | 1,638,400 |
| UXGA | 1600×1200 | 4:3 | 1,920,000 |
| WSXGA+ | 1680×1050 | 16:10 | 1,764,000 |
| WUXGA | 1920×1200 | 16:10 | 2,304,000 |
| TXGA | 1920×1400 | 4:3 | 2,688,000 |
| QXGA | 2048×1536 | 4:3 | 3,145,728 |
| WQXGA | 2560×1600 | 16:10 | 4,096,000 |
| QSXGA | 2560×2048 | 5:4 | 5,242,880 |
| QSXGA+ | 2800×2100 | 4:3 | 5,880,000 |
| WQSXGA | 3200×2048 | 25:16 | 6,553,600 |
| QUXGA | 3200×2400 | 4:3 | 7,680,000 |
| WQUXGA | 3840×2400 | 16:10 | 9,216,000 |
| Sony 4K | 4096×2160 | 1.85:1 | 8,847,360 |
| HSXGA | 5120×4096 | 5:4 | 20,971,520 |
| WHSXGA | 6400×4096 | 25:16 | 26,214,400 |
| HUXGA | 6400×4800 | 4:3 | 30,720,000 |
| WHUXGA | 7680×4800 | 16:10 | 36,864,000 |
Scalable Link Interface (SLI) is a brand name for a multi-GPU solution developed by NVIDIA for linking two (or more) video cards together to produce a single output. SLI is an application of parallel processing for computer graphics, meant to increase the processing power available for graphics. With SLI, it is possible to theoretically double the power of your graphics solution just by adding a second video card with an identical GPU.
The name SLI was first used by 3dfx under the full name Scan-Line Interleave, which was introduced in 1998 and used in the Voodoo2 line of graphics accelerators. When 3dfx collapsed financially, its intellectual property was purchased by NVIDIA. NVIDIA later reintroduced the SLI name in 2004 and intends for it to be used in modern computer systems based on the PCI Express (PCIe) bus. However, the technology behind the name SLI has changed dramatically.
CrossFire is a brand name for ATI Technologies' multi-GPU solution, which competes with its rival nVidia's Scalable Link Interface (SLI). The technology allows a pair of graphics cards to be used in a single computer to improve graphics performance. Although only recently announced for consumer level hardware, similar technology known as AMR has been used for some time in professional grade cards for flight simulators and similar applications available from Evans & Sutherland, ATI had also previously released a similar dual RAGE 128 consumer card called the Fury MAXX.
ATI Crossfire over NVIDIA SLI
DVI (
Digital Visual Interface)The Digital Visual Interface (DVI) is a video interface standard designed to maximize the visual quality of digital display devices such as flat panel LCD computer displays and digital projectors.
The DVI interface uses a digital protocol in which the desired illumination of pixels is transmitted as binary data. When the display is driven at its native resolution, it will read each number and apply that brightness to the appropriate pixel. In this way, each pixel in the output buffer of the source device corresponds directly to one pixel in the display device, whereas with an analog signal the appearance of each pixel may be affected by its adjacent pixels as well as by electrical noise and other forms of analog distortion.
Previous standards such as the analog VGA were designed for CRT-based devices and thus did not use discrete time display addressing. As the analog source transmits each horizontal line of the image, it varies its output voltage to represent the desired brightness. In a CRT device, this is used to vary the intensity of the scanning beam as it moves across the screen.
However, when using digital displays (such as LCD) with analog signals (such as VGA), there is an array of discrete pixels and a single brightness value must be chosen for each. The decoder does this by sampling the voltage of the input signal at regular intervals. When the source is also a digital device (such as a computer), this can lead to distortion if the samples are not taken at the center of each pixel, and there are also problems with crosstalk.
The DVI connector usually contains pins to pass the DVI-native digital video signals. In the case of dual-link systems, additional pins are provided for the second set of data signals.
As well as digital signals, the DVI connector includes pins providing the same analog signals found on a VGA connector, allowing a VGA monitor to be connected with a simple plug adapter. This feature was included in order to make DVI universal, as it allows either type of monitor (analog or digital) to be operated from the same connector.
The DVI connector on a device is therefore given one of three names, depending on which signals it implements:
The connector also includes provision for a second data link for high resolution displays, though many devices do not implement this. In those that do, the connector is sometimes referred to as DVI-DL (dual link).
The long flat pin on a DVI-I connector is longer than the same pin on a DVI-D connector, so it is not possible to connect a male DVI-I to a female DVI-D by removing the 4 analog pins. It is possible, however, to connect a male DVI-D cable to a female DVI-I connector. Many flat screen LCD monitors have only the DVI-D connection so that a DVI-D male to DVI-D male cable will suffice when connecting the monitor to a computer's DVI-I female connector.
DVI is the only widespread video standard that includes analog and digital transmission options in the same connector. Competing standards are exclusively digital: these include a system using low-voltage differential signaling (LVDS), known by its proprietary names FPD (for Flat-Panel Display) Link and FLATLINK; and its successors, the LVDS Display Interface (LDI) and OpenLDI.
Some new DVD players, TV sets (including HDTV sets) and video projectors have DVI/HDCP connectors; these are physically the same as DVI connectors but transmit an encrypted signal using the HDCP protocol for copy protection. Computers with DVI video connectors can use many DVI-equipped HDTV sets as a display; however, due to Digital Rights Management, it is not clear whether such systems will eventually be able to play protected content, as the link is not encrypted.
USB signals are not incorporated into the connector, but were earlier incorporated into the VESA Plug and Display connector used by InFocus on their projector systems, and in the Apple Display Connector, which was used by Apple Computer until 2005.
GTF (General Timing Formula) is a VESA standard which can easily be calculated with the Linux gtf utility.
APIs are different from drivers, which are programs that allow hardware to communicate with a computer's operating system. But as with updated APIs, updated device drivers can help programs run correctly.
Microsoft DirectX is a collection of application programming interfaces for handling tasks related to multimedia, especially game programming and video, on Microsoft platforms. Originally, the names of these APIs all began with Direct, such as Direct3D, DirectDraw, DirectMusic, DirectPlay, DirectSound, and so forth. DirectX, then, was the generic term for all of these Direct-something APIs, and that term became the name of the collection. Over the intervening years, some of these APIs have been deprecated and replaced, so that this naming convention is no longer absolute. In fact, the X has caught on to the point that it has replaced Direct as the common part in the names of new DirectX technologies, including XAct, XInput, and so forth.
Direct3D (the 3D graphics API within DirectX) is widely used in the development of computer games for Microsoft Windows, Microsoft Xbox, and Microsoft Xbox 360. Direct3D is also used by other software applications for visualization and graphics tasks, most notably among the engineering sector for CAD/CAM, because of its ability to quickly render high-quality 3D graphics using DirectX-compatible graphics hardware. As Direct3D is the most widely recognized API in DirectX, it is not uncommon to see the name DirectX used in place of Direct3D.
The interfaces that comprise DirectX include components for use by a running application (runtime components) as well as components for use by software developers at design time (the software development kit). The runtimes were originally redistributed by computer game developers along with their games, but are now included as built-in parts of Microsoft Windows. The SDK is available as a free download. While the runtimes are proprietary, closed-source software, source code is provided for most of the SDK samples.
The latest versions of Direct3D, namely, Direct3D 10 and Direct3D 9Ex, are exclusive to Windows Vista. This is because there were extensive changes in the Windows graphics architecture, and in particular the introduction of the Windows Display Driver Model. This redesign of the graphics infrastructure for Windows Vista supports virtualizing graphics hardware to multiple applications and services such as the Desktop Window Manager, in contrast to the exclusive access afforded to DirectX applications on Windows XP. Both Direct3D 9Ex and Direct3D 10 rely on the WDDM infrastructure and WDDM drivers.
OpenGL (Open Graphics Library) is a standard specification defining a cross-language cross-platform API for writing applications that produce 2D and 3D computer graphics. The interface consists of over 250 different function calls which can be used to draw complex three-dimensional scenes from simple primitives. OpenGL was developed by Silicon Graphics Inc. (SGI) in 1992 and is widely used in CAD, virtual reality, scientific visualization, information visualization, flight simulation. It is also used in video games, where it competes with Direct3D on Microsoft Windows platforms (see Direct3D vs. OpenGL).
