Glossary » A

Advanced Configuration and Power Interface - a standard for power management in desktop and notebook computers. It allows the user to control standby timers or the powering down of the display, hard drive or even the whole PC. ACPI also allows for automatic power saving features in modern notebook and desktop computers.

Advanced Communications Riser - a connector for certain add-on cards, most commonly used for sound upgrades. The way ACR cards are designed makes them proprietary to the motherboard they ship with, as different manufacturers add different features to their ACR cards. The advantage of ACR is that the slot has a direct bus to the southbridge of the motherboard and thus avoids some of the congestion that is common over the PCI bus. Many of the integrated features of the southbridge, such as sound, modem, networking and even Firewire can be routed trough the ACR bus to the riser card to give you physical ports on the back of the PC. The ACR specification was developed by VIA and AMD in response to Intel’s CNR technology.

This is a method of addressing an array of liquid crystal cells that make up the pixels of a flat-panel display. Each pixel is attached to and controlled by a thin film transistor (TFT) usually made of amorphous silicon (a-Si). Because each transistor can hold the voltage applied to each pixel either in an on or off state until the next time the screen refreshes, active matrix TFT displays are brighter, have better viewing angles and are more responsive than passive matrix displays. However, as the active matrix is etched in a similar way to CPUs, this procedure makes active matrix displays more expensive.

Asymmetric Digital Subscriber Line. Allows standard telephone lines to transmit data and voice calls at the same time by using different channels. This is achieved with a ‘splitter’ which is fitted to your existing telephone wall socket during installation.

Auto Focus or Anisotropic Filtering Auto Focus: The system used by either a camera lens or less commonly a camera body, to automatically focus the image of a selected part of the scene. This can be done by measuring the phase of light hitting the CCD or CMOS sensor or by firing an infrared beam to measure the distance between the subject and camera. Anisotropic Filtering: From the Greek word "an" meaning "not," and "isos" meaning "equal", Anisotropic filtering is the most demanding of the currently used texture filtering techniques. That said, it also offers the best quality, primarily when used for textured surfaces that are viewed at acute angles. It’s also the most difficult to explain in simple terms. If you imagine firing a paint ball at a wall that’s facing you it should leave a roughly circular paint blot. If this paint blot was a pixel then it would exhibit equal amounts of colour data in the horizontal, vertical and diagonal planes. This would require a form of “isotropic” or “equal” filtering such as Bilinear or Trilinear to be used. Now let’s imagine we’re in a long corridor and we fire the paint ball at one of the walls to the side and in front of us. Because of the angle we’re at we now have a paint blot that’s more elliptical in shape being longer on its horizontal axis than it is on its vertical axis. In this situation we need to modify our filtering technique so it takes more data samples in one axis than it does in the other. Hence we need a “not equal” or “anisotropic” filtering method. Different levels of quality can be achieved by varying the number of texture samples, or taps, that are required to calculate each texel and this can be used to increase or decrease the demands on the graphics card and thus balance performance with quality.

Accelerated Graphics port. A high speed (528 Mbytes/sec) 32 bit data bus introduced in 1997 to accommodate the high speed transmission of texture data to and from system memory via an AGP compatible graphics card.

This is the amount of system memory that your graphics hardware reserves for the storage of textures if they are too large to be stored in dedicated video memory. These textures are transferred across the AGP bus. 64MB or 128MB are considered the norm and are usually optimal.

The pixels from which an image is built contain four channels of data that define how the pixel appears on screen. These four channels consist of one for red, one for green, one for blue and an alpha channel, which is used to specify the level of transparency. The alpha channel can be assigned a value between 0 and 1 where 0 is completely transparent and 1 is completely opaque. This value is know as its “weighting”. Alpha blending may be used to create water, windows and other translucent parts of a 3D scene.

Used to indicate transparent areas in video or still images, also know as a Key.

From the Greek word "an" meaning "not," and "isos" meaning "equal", Anisotropic filtering is the most demanding of the currently used texture filtering techniques. That said, it also offers the best quality, primarily when used for textured surfaces that are viewed at acute angles. It’s also the most difficult to explain in simple terms. If you imagine firing a paint ball at a wall that’s facing you it should leave a roughly circular paint blot. If this paint blot was a pixel then it would exhibit equal amounts of colour data in the horizontal, vertical and diagonal planes. This would require a form of “isotropic” or “equal” filtering such as Bilinear or Trilinear to be used. Now let’s imagine we’re in a long corridor and we fire the paint ball at one of the walls to the side and in front of us. Because of the angle we’re at we now have a paint blot that’s more elliptical in shape being longer on its horizontal axis than it is on its vertical axis. In this situation we need to modify our filtering technique so it takes more data samples in one axis than it does in the other. Hence we need a “not equal” or “anisotropic” filtering method. Different levels of quality can be achieved by varying the number of texture samples, or taps, that are required to calculate each texel and this can be used to increase or decrease the demands on the graphics card and thus balance performance with quality.

Often referred to as AA or FSAA (Full Scene Anti-Aliasing). Trying to create a sloping edge with square pixels is like trying to create a sloping edge with building blocks, there’s always a step effect that ruins its appearance. Anti-aliasing is a method for adjusting the colour of these offending pixels so they blend better with the background and so become less noticeable.

The diameter of the objective lens in an optical system. The bigger the aperture, the greater it’s light gathering capability. Since typical photographic lenses feature multiple elements, the aperture is the effective light gathering capability of the system as a whole. By placing an adjustable iris at the far end, the aperture and hence exposure can be controlled.

Unlike the holes found in a shadow mask, aperture grille displays use a type of mask consisting of very fine vertical wires to clean and line up the electron beams with their respective red, green and blue phosphor lines. Because there is no masking in the horizontal direction, more energy from the electrons passes through to the phosphor resulting in a brighter and more vivid picture. However, these wires are sensitive to vibrations and have to be held in place by two horizontal damping wires that are just visible to the naked eye.

Exposure mode which allows manual control of the lens iris, while automatically adjusting the shutter speed to compensate and deliver a correct exposure. Adjusting the iris diameter (described by its “f-number”) allows control over the depth of field.

Application Programming Interface. In its simplest terms an API is a set of useful functions that can be accessed by programmers to achieve certain goals. An API may restrict, enhance or redirect what a programmer can achieve through a given command set or how those commands are put into practise.

Anti-Reflective, Anti-Glare coating used on monitor screens.

Undesirable elements on an image introduced through limitations of a digital device, processing or compression system. Typically reveal themselves on the image as snow-like noise, random speckles, blocks or banding.

The shape of an image. The majority of computer monitors use a 4:3 aspect ratio, but many are now employing a 16:9 widescreen aspect ration similar to widescreen TVs. Most digital camera images have a 4:3 aspect ratio which matches the shape of traditional non-widescreen TVs. Many models offer a wider 3:2 aspect ratio which matches the shape of 35mm film, but most do so by simply cropping the top and bottom of a 4:3 image.

AMD’s brand name for its consumer level performance CPUs.

Stands for Advanced Technology eXtended. This is the standard motherboard form factor used in modern PCs. It was developed in the early 1990’s by Intel as a replacement for the older AT standard which lacked integrated ports, suffered from poor thermal design and had no power management. Today all consumer motherboards follow the ATX standard which makes it much easier when you are looking at changing your motherboard. There is also a standard for ATX power supplies that makes it much easier to choose a suitable power supply for your motherboard.

Commonly found on LCDs this is a function that automatically adjusts the pixel clock, phase and sometimes the screen position when the LCD is connected to an analogue signal.

Audio Video Interleave. A file format developed by Microsoft that can be used to store video with a variety of codecs.