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An electronic display that allows a user to interact with a computer system by touching an area or areas on the display. Touch-screen displays have been in use for many years in ATMs, checkout registers, and other applications, but gained mass…

An early mechanical calculator. The abacus likely originated in Babylonia sometime before 1000 BCE. Over the subsequent centuries, it became a commonplace device in many regions of the world. The abacus is still occasionally used as a cognitive…

A discipline that deals generally with the extraction of information from acoustic signals in the presence of noise and uncertainty. Acoustic signal processing has expanded from the improvement of music and speech sounds and a tool to search for oil…

A group of software development methods in which requirements and solutions evolve through collaboration between the developers and the customers. Agile methods have significantly changed the practice of software development since their inception…

The subfield of computer science concerned with understanding the nature of intelligence and constructing computer systems capable of intelligent behavior. Many activities, such as perception, learning, planning, natural language, and understanding,…

A binary digit. In the computer, electronics, and communications fields, “bit” is generally understood as a shortened form of “binary digit.” In a numerical binary system, a bit is either a 0 or 1. Bits are generally used to indicate situations that…

A system that receives and processes television signals, as well as other digital forms of communications such as those related to high-speed Internet connectivity and cable telephony, from various sources and retransmits these signals through…

Desktop or, more often, portable electronic devices that are used to perform arithmetic, statistical, or other, more complex processing operations at the step-by-step direction of the user or by execution of a program (a stored sequence of…

A method of gathering best practices for various work processes into coherent groupings to facilitate quality and process improvement. Capability Maturity Models® (CMM®) represent a relatively recent step in the evolution of process improvement…

A periodic waveform upon which an information-bearing signal is impressed. This process is known as modulation and comprises a variety of forms such as amplitude, phase, and frequency modulation. The most common type of carrier is the sinusoidal…

Cameras in mobile phones or smartphones that can capture images and videos.The cellphone, the world’s favorite must-have gadget, has been with us for nearly a half-century, while experiencing continuous and often phenomenal improvements. Much of the…

A cellular automaton is a hypothetical computer constructed of a regular array of cells that interact with neighboring cells according to a set of simple rules. Though conceptually simple, cellular automata can produce complex and surprising…

A computing system that is composed of two logical parts: a server, which provides services, and a client, which requests them. The two parts can run on separate machines on a network, allowing users to access powerful server resources from their…

A service, primarily for deaf people, that allows individual viewers to display the dialog of a television program in a readable form on the television screen. In the United Kingdom the service is called subtitling. Closed-caption television was…

The use of video cameras to transmit a signal to a particular limited audience at one or more specific locations via coaxial cables, telephone wires, fiber-optic strands, microwave radio systems, or communications satellites, as compared to openly…

An electrical transmission line comprising an inner, central conductor surrounded by a tubular outer conductor. The two conductors are separated by an electrically insulating medium which supports the inner conductor and keeps it concentric with the…

A cable that transmits information signals between geographically separated points. The heart of a communications cable is the transmission medium, which may be optical fibers, coaxial conductors, or twisted wire pairs. A mechanical structure…

A means for ensuring the privacy of voice, data, and video transmissions. While analog techniques were commonly utilized to perform such functions in the past for voice and video, when signals were transmitted in analog form, these techniques are…

The protection of wire and optical communications systems equipment and service from electrical disturbances. This includes the electrical protection of lines, terminal equipment, and switching centers, and inductive coordination, or the protection…

A system for data storage in which digitally encoded information in the form of microscopic pits on a rotating disk is accessed by optical readout. The compact disk (Fig. 1) was originally developed as a music carrier providing high fidelity, random…

A branch of computer science that deals with the theory and techniques of computer-generated images. Computers produce images by analyzing a collection of dots, or pixels (picture elements). Computer graphics is used to enhance the transfer and…

Any device connected internally or externally to a computer and used in the transfer of data to or from a computer. A personal computer (PC) or workstation processes information. Data (unprocessed information) must get into the computer, and the…

The process of protecting against threats to computing systems. A threat is an event that can cause harm to computers, data or programs, or computations (Fig. 1). A failure of computer security occurs because of a vulnerability or weakness in a…

The technology concerned with computational understanding and use of the information present in visual images. In part, computer vision is analogous to the transformation of visual sensation into visual perception in biological vision. For this…

The application of specialized computer software to the design, simulation, and physical layout of electronic circuits on semiconductor chips and circuit boards. Integrated circuits Printed circuit boardDesigning integrated circuits is extremely…

Complex systems in which computers play a major role. While complex physical systems and sophisticated software systems can help people to lead healthier and more enjoyable lives, reliance on these systems can also result in loss of money, time, and…

The simultaneous execution of several interrelated computer programs. A sequential computer program consists of a series of instructions to be executed one after another. A concurrent program consists of several sequential programs to be executed in…

A directional antenna consisting of the combination of a reflector comprising two conducting planes forming a dihedral angle and a driven radiator or dipole which usually is in the bisecting plane. It is widely used both singly and in arrays, gives…

Interference in a communications channel (disturbed channel) caused by activity in other communications channels (disturbing channels). The term was originally used to denote the presence in a telephone receiver of unwanted speech signals from other…

The various mechanisms for data confidentiality, data authentication, and nonrepudiation (that is, the property to prevent the denial of previous commitments or actions). Cryptography, with a long history of being an art of secret writing, has…

The exchange of data between two devices over a communications medium. The development of data communications and networking technologies has had a profound impact on all aspects of modern life. Arguably, no other technology has affected more people…

The process of transforming information from one representation to another smaller representation from which the original, or a close approximation to it, can be recovered. The compression and decompression processes are often referred to as…

The techniques used to transform massive datasets into a more suitable, or smaller, form for data analysis, while preserving the intrinsic characteristics of the data and minimizing the loss of accuracy. Data reduction is used for scientific…

A multidisciplinary field for analyzing large amounts of data—current and past (historical)—which are processed using tools and methods from statistics, applied mathematics, artificial intelligence, and computer programming, with the object of…

A means of storing a collection of data. Computer science is in part the study of methods for effectively using a computer to solve problems, or in other words, the entire process of determining exactly the problem to be solved. This process entails…

A data warehouse is an automated warehouse where related information is stored. Users can have access to large amounts of consistent, organized, and related information in a data warehouse. It is advantageous to have access to information from…

An alternative to the sequential, or von Neumann–based, model of computing, offering an inherently parallel metaphor. The dataflow concept is characterized by an orientation toward producing and consuming data values rather than updating storage…

Using an artificial intelligence technique known as deep learning and high-resolution remote sensing, scientists have counted and mapped the location of trees in 11,000 satellite images covering more than 1.3 million square kilometers (500,000…

A device that recovers from a transmitted signal information that has been embedded in the signal by a process of modulation. The modification of a usually sinusoidal electrical carrier signal (or simply carrier) for the purpose of transmitting…

A device which, in its simplest form, provides an output that corresponds to the number of pulses applied to its input. Types Counters may take many forms: geared mechanisms (water meters, odometers), relays (early telephone switch gear), vacuum…

Text, numerals, sound, or images (both moving and still) that are either stored or transmitted in a binary form and have potential use as evidence to prove a circumstance or event in a court of law. Binary refers to the electronic code made up of…

An Internet-based global naming and resolution system that provides for the precise identification, retrieval, and trading of digital items in the form of articles, books, images, bibliographies, supporting data, videos, charts, tables, audio, and…

A device for converting information in the form of combinations of discrete (usually binary) states or a signal to information in the form of the value or magnitude of some characteristics of a signal, in relation to a standard or reference. Most…

A four-port waveguide device (Fig. 1) in which an incoming wave at any one port (for example, A) appears at two others (C and D), but not at the fourth (B). This device has numerous applications in wave-guide networks such as microwave waveguides,…

A distributed system consists of a collection of autonomous computers linked by a computer network and equipped with distributed system software. This software enables computers to coordinate their activities and to share the resources of the system…

Programmable computers integrated with electrically powered machines that perform household chores. Domestic robots, also known as home or service robots, are essentially programmable computers integrated with electrically powered machines that…

A transmission network used to selectively modify the components of a signal according to their frequencies. In most cases a filter is used to enhance signals of desired frequencies while suppressing signals of undesired frequencies. An ideal filter…

That branch of electrical engineering dealing with the transmission and reception of information. Information can be transmitted over many different types of pathways, such as satellite channels, underwater acoustic channels, telephone cables, and…

Disturbance to the normal or expected operation of electrical or electronic devices, equipment, and systems. Electrical interference is sometimes called radio-frequency interference (RFI) or electromagnetic interference (EMI). Such disturbances may…

The connection of a specific circuit (called the load) to another circuit. Illustrationa shows a source of electrical energy (S), a coupling circuit (C), and a load (L). In power transmission, S is the generator of the power plant, C represents…

Interfering and unwanted currents or voltages in an electrical device or system. Electrical noise, or simply noise, has a significant effect on the design and operation of almost all electrical and optical systems which are used to communicate or…

A device that produces electrical noise for use in electrical measurements. Electrical noise generators are commonly employed to measure the noise figure or noise temperature of radio receivers. They are also used in various other tests in radar and…

The imposition of a metal or composite barrier between one or more sources of electrical noise and their victims with the objective of reducing or eliminating electrical interference. Examples of the barrier are the case or housing of equipment;…

The situation in which electrical and electronic de­vices and systems work as intended, both within themselves and in their electromagnetic environment.Electromagnetic interference (EMI) is said to exist when unwanted voltages or currents are…

Devices which are used to capture the sound waves of conversation originating in an ostensibly private setting in a form, usually as a magnetic tape recording, which can be used against the target by adverse interests.There are two kinds of…

The asynchronous transmission of messages by using computers and data-communication networks. Historically, electronic mail (or e-mail) referred to any of a number of technologies that allowed people to send documents to one another through…

The art and science of preserving the use of the electromagnetic spectrum for friendly forces while denying its use to the enemy. This is accomplished via use of techniques, devices, and equipment by an adversary to deny or counteract an enemy's use…

Computer systems that cannot be programmed by the user because they are preprogrammed for a specific task and are buried within the equipment they serve. The term derives from the military, where computer systems are generally activated by the flip…

Methods and techniques for constructing human-machine systems with specialized problem-solving expertise. The pursuit of this area of artificial intelligence research has emphasized the knowledge that underlies human expertise and has simultaneously…

Systems, predominantly computing systems, communication systems, and other computer-based systems, which tolerate undesired changes in their internal structure, internal state, or external environment. Such changes, generally referred to as faults,…

The path of information travel, usually from one electrical system to another, in which light acts as the information carrier and is propagated by total internal reflection through a transparent optical waveguide. An electrooptic modulator and an…

Very large scale integrated (VLSI) circuits that can be electrically programmed to implement complex digital logic. By combining many of the advantages of custom chips with the programmability of microprocessors, they are useful in a wide range of…

A technique used in telecommunications transmission systems whereby the instantaneous frequency of a carrier signal is determined by the characteristics of an information signal, the so-called modulating signal. Frequency modulation (FM) is a form…

An electronic circuit or device producing frequency modulation. This device changes the frequency of an oscillator in accordance with the amplitude of a modulating signal. If the modulation is linear, the frequency change is proportional to the…

A device for the detection or demodulation of a frequency-modulated (FM) wave. Frequency-modulation detectors operate in several ways. In one class of detector, known as a discriminator, the frequency modulation is first converted to amplitude…

Radio transmission accomplished by variation of the frequency aspect of a radio-frequency (RF) carrier signal by an input signal (called the modulating signal). The frequency-modulation (FM) technique was invented by Major Edwin A. Armstrong in the…

Search procedures based on the mechanics of natural selection and genetics. Such procedures are known also as evolution strategies, evolutionary programming, genetic programming, and evolutionary computation. Originating in the cybernetics movement…

A nondestructive technique using electromagnetic waves to locate objects or interfaces buried beneath the Earth's surface or located within a visually opaque structure; also termed ground-probing, surface-penetrating, or subsurface radar. Principle…

A linear, passive, two-port electric circuit element whose transmission properties are such that it is effectively a half wavelength longer for one direction of transmission than for the other direction of transmission. Thus a gyrator is a device…

The principle that multiple frequencies applied to a nonlinear device produce new frequencies that are sums and differences of the applied frequencies and their harmonics. Heterodyning, or mixing, is the process of multiplying a weak signal by a…

The field of engineering involving computer-based hardware and software systems, and communication systems, to enable the acquisition, representation, storage, transmission, and use of information. Information technology (IT) is critically dependent…

An attempt to formulate the grammar of a language in mathematical terms. Language theory is an important area of linguistics and computer science. Formal language theory was initiated in the mid-1950s in an attempt to develop theories on natural…

The optical analog of radar. The term lidar is an acronym for light detection and ranging. Lidar systems employ intense pulses of light, typically generated by lasers, and large telescopes and sensitive optical detectors to receive the reflected…

Computer networks that usually cover a limited range, for example within the boundary of a building or a campus. A computer network is two or more computers that communicate with each other. The primary usage of local-area networks (LANs) is the…

The basic building blocks used to realize consumer and industrial products that incorporate digital electronics. Such products include digital computers, video games, voice synthesizers, pocket calculators, and robot controls.Calculators Digital…