Chapter 7 Systems Architecture
font
A collection of characters of similar style and appearance.
24-bit color
A color display scheme that represents each pixel's color as three 8-bit numbers, each representing the intensity of an additive or a subtractive color; results in chromatic depth of around 16 million colors. See also chromatic depth.
Graphics Interchange Format (GIF)
A common bitmap compression format for still images
Joint Photographic Experts Group (JPEG)
A common bitmap compression format for still images.
speech synthesis
A complex process for generating human speech based on character or text input.
video controller
A device connected to the system bus (or a dedicated video bus) that accepts commands and data from the CPU and generates analog or digital video signals, which are transmitted to the monitor.
digitizer
A device consisting of a digitizing tablet and a pen, stylus, or both that captures a pointing device's position as input data.
photosensor
A device that converts incoming light energy into outgoing electrical energy.
optical scanner
A device that generates bitmap representations of printed images; detects light reflected from the page with an array of photosensors.
audio response unit
A device that generates spoken messages based on text input; commonly used for automated phone bank tellers and automated call routing.
grayscale
A display device or encoding method that can display black, white, and shades of gray but no other colors.
monochrome
A display device or encoding method that can display only one of two colors (usually black and white), so it requires only 1 bit per pixel
input pad
A general class of input devices that convert pressure into input, such as for capturing signatures or drawings; these devices typically use infrared detectors, photosensors, pressure-sensitive pads, or magnetic fields.
PostScript
An Adobe image description language designed mainly for printed documents, although it's also a programming language for generating video display output.
Portable Document Format (PDF)
An Adobe image description language developed to generate and manage documents as an integrated whole rather than a collection of independent images and pages.
passive matrix display
An LCD that shares transistors among rows and columns of pixels.
active matrix display
An LCD that uses one or more transistors for every pixel.
pixel
An abbreviation of "picture element," it's a single unit of data in an image; also refers to a single point on a display surface.
digital-to-analog converter (DAC)
An audio device that accepts a bitstream representing sound samples and generates a continuous analog signal that can be amplified and routed to a speaker.
analog-to-digital converter (ADC)
An audio device that accepts a continuous electrical signal representing sound, samples it at regular intervals, and outputs a bitstream representing the samples. See also sampling.
video display terminal (VDT)
An early I/O device containing an integrated keyboard and TV screen; capable of displaying only text and primitive graphics.
sound card
An expansion card connected to the system bus that contains components for sound input and output.
dot matrix printer
An impact printer that moves a print head containing a matrix of pins over the paper, and a pattern of pins matching the character or symbol to be printed is forced out of the print head.
cathode ray tube (CRT)
An older video display device that's an enclosed glass vacuum tube with an electron gun generating a narrow beam of electrons toward the tube's front surface, which is coated with colored phosphors that emit light when struck by electrons.
bar-code scanner
An optical input device that detects specific patterns of bars or boxes representing numeric data.
mark sensor
An optical input device that scans for light or dark marks at specific locations on a page.
scanning laser
Devices that sweep a narrow laser beam back and forth across bar codes. See also bar-code scanner.
subtractive colors
In printing, the primary colors are generated by using the inverse of the primary video display colors, so cyan is the absence of red, magenta is the absence of green, and yellow is the absence of blue.
RGB
Red, green, and blue; the primary colors for video display.
speaker dependent
Requiring training to recognize the sounds of human speakers; a characteristic of speech-recognition systems. See also speech recognition.
chromatic depth
The number of distinct colors or gray shades that can be displayed in a grayscale image. See also grayscale.
resolution
The number of pixels displayed per linear measurement unit.
refresh rate
The number of refresh cycles per second on a video display device; normally stated in hertz. See also refresh cycle.
monitor
Video display panels. The term also refers to hardware or software that tracks and reports processing or I/O activity. See also hardware monitor and software monitor.
phoneme
Vocal sounds that are basic components of human speech; they correspond roughly to the sounds of each letter of the alphabet..
bar code
A series of vertical bars of equal length but varied thickness and spacing, used to encode numeric data.
Musical Instrument Digital Interface (MIDI)
A standard for storing and transporting control information between computers and electronic musical instruments and synthesizers.
point
A standard measurement unit for font size; equals 1/72 of an inch.
bitmap
A stored set of numbers describing the content of all pixels in an image.
cursor
A symbol on a video display that indicates the current position; also called a "pointer."
palette
A table of colors used to represent pixel color; the number of bits used to represent each pixel determines the table size.
thin film transistor (TFT)
A technology for manufacturing active matrix displays, in which wiring and transistors are added in thin layers to a glass substrate; similar to semiconductor fabrication technology.
Optical character recognition (OCR)
A technology that combines optical-scanning technology with a special-purpose processor or software to interpret bitmap content. See also optical scanner.
video RAM (VRAM)
A type of RAM type used in a video controller; differs from ordinary RAM because it can be written by the bus interface circuitry or video processor while being read by display generator circuitry. See also dual-porting.
OpenGL
A video controller image description language developed by Silicon Graphics but now maintained by Khronos Group as an open standard.
Direct3D
A video controller image description language that's part of the Microsoft DirectX suite embedded in Windows OSs.
liquid crystal display (LCD)
A video display device containing liquid crystals sandwiched between two polarizing filter panels; the crystals change from opaque to transparent when an electrical charge is applied.
plasma display
A video display device that uses an active matrix display and generates light by applying an electrical charge to neon gas.
light-emitting diodes (LEDs)
A video display technology that uses phosphorescent compounds to produce red, green, and blue light.
CMY
Cyan, magenta, and yellow; the primary colors in printing. See also subtractive colors.
CMYK
Cyan, magenta, yellow, and black; represents the primary colors in printing plus a separate ink for black.
refresh cycle
In dynamic RAM, the period during which circuitry supplies fresh infusions of power automatically; read and write operations can't be performed during this cycle. Also refers to the transfer of a full screen of data from the display generator to the monitor.
vector
In graphics, a line segment with a specific angle and length in relation to a point of origin; also refers to a one-dimensional array.
flat panel displays
Newer video display devices that are thinner, generate higher quality images, and consume less power than CRTs.
half-toning
Simulating shades of gray by dithering black and white dots. See also dithering.
scan code
A 1- or 2-byte data element generated by a keyboard controller; represents a specific keyboard event. See also keyboard controller.
image description language (IDL)
A language (usually device independent) that uses compact bit strings or ordinary ASCII or Unicode text to describe primitive image components, such as straight lines and simple shapes; reduces storage space requirements because a description of a simple image component is usually much smaller than a bitmap.
dots per inch (dpi)
A measure of print or display resolution (pixel density); a smaller pixel size represents a higher dpi and, therefore, higher image or print quality. See also resolution.
keyboard controller
A microprocessor integrated into a keyboard that generates a bitstream output of scan codes according to an internal program or lookup table. See also scan code.
digital signal processor (DSP)
A microprocessor specialized for processing continuous streams of audio or graphical data; commonly embedded in audio and video hardware.
large-format printer
A more current term for plotters. See also plotter.
organic LED (OLED)
A newer LED, manufactured with TFT technology, that achieves high-quality color display with organic compounds. See also light-emitting diodes (LEDs) and thin film transistor (TFT).
plotter
A printer that generates line drawings on sheets or rolls of paper up to 64 inches wide. See also large-format printer.
laser printer
A printer that operates by charging areas of a photoconductive drum; toner is attracted to charged areas of the drum and then to paper.
inkjet printer
A printer that produces printed images by placing small drops of liquid ink onto paper; ink is forced out of the nozzle by mechanical movement or by heat.
dithering
A process that generates continuous color approximations by placing small dots of different colors in an interlocking pattern.
vector list
A series of concatenated or linked vectors that can be used to construct complex shapes; images constructed from a vector list resemble connect-the-dots drawings
polyphonic
Capable of generating many frequencies (notes) simultaneously.
monophonic
Capable of generating only one frequency (note) at a time.
additive colors
The primary colors for video display (red, green, and blue).
sampling
The process of converting analog sound waves to digital representation; it analyzes the content of the audio sound spectrum many times per second and converts it to a numeric representation.
speech recognition
The process of recognizing and responding to the meaning embedded in spoken words, phrases, or sentences.
dual porting
The simultaneous read/write capability in video RAM.