Display adapter problems constitute another major component of our service calls, and usually require immediate attention - you can't work on a computer when you can't see anything on the screen. Display adapters are a rapidly evolving technology. You should understand what's out there, and how to deal with it's problems. In addition, it's important to remember that other problems are easily disguised as video problems. Such problems include bad RAM, too much dust, and poorly seated cable connections. Remember: If the computer is turned on, and the drive spins, the problem is likely to involve video.

The two major types of display adapters
pci | agp | agp slot on the motherboard | screenshots


How display adapters work
schematic | gpu | video memory | ramdac | drivers


Graphics terms
pixel | resolution | dithering | color depth | rendering | 3D acceleration | anti-aliasing | direct x | open gl


Other links
Troubleshooting display adapters | Current display adapters | Display adapter vendor sites

GPU - Graphics Processing Unit
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The processor onboard the board which controls all aspects of image rendering.
The gpu executes instructions interpreted by the adapter's driver.
Frame data is written to the frame buffer ( a memory space which holds graphics instructions) by the gpu much faster than by the main system cpu. Thus, since there's less data congesting the main board bus, the CPU works less.
GPU's are recognized by their heat sinks, and, in many cases, by their own cooling fans.


Video Memory
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All non-integrated display adapters have their own onboard memory. In addition, higher-end laptops have memory separate from main system RAM, dedicated to AGP video. There are several different kinds of video memory. Early systems used conventional DRAM (dynamic ram) which degraded performance because of its high refresh rate and power requirements.

shared video memory | video ram (vram) | windows ram (ram) | edo dram | sdram | sgram | drdram


Shared video memory: On lower end systems, the video is integrated into the motherboard. The video controller uses a certain amount of 'shared RAM' for video memory. The shared ram (usually 8 mb) is taken away from main system RAM. Thus, on a 64 Mb system, if the integrated controller uses '8 Mb shared video RAM', the main system only uses 56 Mb of RAM, and this is the number you'll see when checking for the memory.


Video RAM (VRAM): Dual-ported Dynamic RAM. Dual porting means that the memory space can be written to and read from at the same time, unlike conventional RAM. Video RAM is faster than conventional DRAM.


Windows RAM (WRAM): Not to be associate with the Windows OS. Dual ported as well, and runs faster than VRAM. Some Matrox cards use WRAM. Dual ported.


EDO DRAM: More efficient than DRAM, but not used in current higher end cards. Cannot support bus speeds above 66 MHz. Single ported.


Synchronous Dynamic Ram (SDRAM): Memory and graphics chips run on a common clock (are synchronized). Thus, SDRAM runs much faster than EDO. Single ported.


Synchronous Graphics Ram (SGRAM): Similar to SDRAM but faster. Single ported. DDR SGRAM is quite popular.


DRDRAM: The newest type of video memory. It is anticipated that drdram will be much faster than any current video memory. Single ported.



RAMDAC
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A chip on the motherboard that converts the data in the frame buffer ( the memory space that holds the image), and converts it into the analogue RGB signal for output to the monitor. DAC means 'digital to analogue converter'. The RAMDAC reads the contents of the video memory, and converts it to RGB.


Drivers
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Translates the graphics requirements of a system into instructions that are executed by the display adapter. The driver translates pixel values, line drawing, shape drawing, etc. A driver's performance can vary depending on resolution. Some drivers don't perform as well at resolutions not 'native' to the adapter. This is an effect seen more frequently in modern laptops.

GRAPHICS TERMS
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Pixel

The smallest controllable element on a screen. Consists of one red (R), one green (G), and one blue (B) phosphor. The pixel can be set to any color depending on the adapter, drivers, etc.

Resolution

Sharpness of the digital image. Associated with the 'dot pitch' A 'dot' is a pixel. The higher the resolution, the greater the number of pixels that can be displayed at one time. The resolution is represented as the number of pixels in a row times the number of pixels in a column. As video standards evolved, the resolution increased. Thus, VGA (video graphics array) supports 640x480 resolution while SXGA (super extended graphics array) and UXGA (ultra xga), both current standards, support 1280x1024 and 1600x1200, respectively. Below is a schematic of differing resolutions




Dithering

The system substitutes combinations of colors for colors the adapter cannot natively produce. This results in a degradation of image.

Color Depth

The number of colors an adapter can display. Represented by the number of colors or a term defining a number of colors:

- VGA color mode: 16 colors
- 256 colors: 256 shades of red, green, and blue. Uses 1 byte (8 bits) per pixel for color info.
- High Color: 65,536 (usually referred to as 65,000 colors). Uses 2 bytes (16 bits) per pixel for color info.
- True Color: 16,777,216 (usually referred to as 'millions of colors'). Uses 3 bytes (24 bits) per pixel for color info.

The more bits used for color info, the greater the color depth.

Rendering

The process of drawing the pixels by the hardware. The faster the video memory (the faster the frame buffer can be read from and written to), the faster the rendering. Gives the illusion of movement by refreshing each frame about 30 times per second. Associated with 3D. For details on the specifics of rendering, click here.

3D Acceleration

A hardware engine on the adapter (the gpu) dedicated to executing the instructions to render 3 dimensional images. 3D accelerators draw millions of 'polygons' per second, delivering 3D without bottlenecking the main board CPU.

Anti-Aliasing

The act of smoothing objects such as diagonal lines, which can appear as 'stepped' instead of smoothly diagonal. The image is sampled over itself several times in order to remove the 'artifacts' (the steps), and create a smooth line.

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