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Encyclopedia > Digital

A digital system is one that uses discrete values (often electrical voltages), representing numbers or non-numeric symbols such as letters or icons, for input, processing, transmission, storage, or display, rather than a continuous range of values (ie, as in an analog system). Digital have multiple potential meanings: For the Digital company see Digital Equipment Corporation. ... For other uses, see Letter (disambiguation). ... Look up icon in Wiktionary, the free dictionary. ... In mathematics, the word continuum sometimes denotes the real line. ... An analog or analogue signal is any time continuous signal where some time varying feature of the signal is a representation of some other time varying quantity. ...


The distinction between "digital" and "analog" can refer to method of input, data storage and transfer, or the internal working of a device. The word comes from the same source as the word digit and digitus: the Latin word for finger (counting on the fingers) as these are used for discrete counting. Digit may refer to: A finger or a toe Numerical digit, as used in mathematics or computer science Digit (unit), an ancient meterological unit Digit (magazine), an Indian information technology magazine This is a disambiguation page: a list of articles associated with the same title. ... For other uses, see Latin (disambiguation). ... This article does not cite any references or sources. ...


The word digital is most commonly used in computing and electronics, especially where real-world information is converted to binary numeric form as in digital audio and digital photography. Such data-carrying signals carry one of two electronic or optical pulses, logic 1 (pulse present) or 0 (pulse absent). RAM (Random Access Memory) Look up computing in Wiktionary, the free dictionary. ... This article is about the engineering discipline. ... The binary numeral system, or base-2 number system, is a numeral system that represents numeric values using two symbols, usually 0 and 1. ... Digital audio comprises audio signals stored in a digital format. ... 10 MP Nikon D200 and a Nikon film scanner The Canon EOS 350D The Canon PowerShot A95 Digital photography, as opposed to film photography, uses electronic devices to record and capture the image as binary data. ...

Contents

Digital noise

When data are transmitted, or indeed handled at all, a certain amount of noise enters into the signal. This can have several causes: data transmitted by radio may be received inaccurately, suffer interference from other radio sources, or pick up background radio noise from the rest of the universe. Microphones pick up everything—signal as well as background noise—without discriminating between signal and noise, so when audio is encoded digitally, it already includes noise. This article is about noise as in sound. ... For other uses, see Interference (disambiguation). ...


Electric pulses being sent via wires are attenuated by the resistance of the wire, and changed by its capacitance or inductance. Temperature variations can increase or reduce these effects. While digital transmissions are also degraded, slight variations do not matter since they are ignored when the signal is received. With an analog signal, variances cannot be distinguished from the signal and so are a kind of distortion. In a digital signal, similar variances will not matter, as any signal close enough to a particular value will be interpreted as that value. Care must be taken to avoid noise and distortion when connecting digital and analog systems, but more when using analog systems.


Symbol to digital conversion

Since symbols (eg, alphanumeric characters) are not continuous, converting symbols to digital form is rather simpler and less prone to data loss than analog to digital conversion. Instead of sampling and quantization as in D/A conversion, such techniques as polling and encoding are needed. Generally speaking, the term alphanumeric refers to anything that consists of only letters and numbers. ... In computer science the term Polling refers to actively sampling the status of an external device by a client program as a synchronous activity. ... A character encoding or character set (sometimes referred to as code page) consists of a code that pairs a sequence of characters from a given set with something else, such as a sequence of natural numbers, octets or electrical pulses, in order to facilitate the storage of text in computers...


A symbol input device usually consists of a number of switches are polled at regular intervals to see which switches are pressed. Data will be lost if, within a single polling interval, two switches are pressed, or a switch is pressed, released, and pressed again. This polling can be done by a specialized processor in the device to prevent burdening the main CPU. When a new symbol has been entered, the device sends an interrupt to alert the CPU to read it. “CPU” redirects here. ... In computing, an interrupt is an asynchronous signal from hardware or software indicating the need for attention. ...


For devices with only a few switches (such as the buttons on a joystick), the status of each can be encoded as bits (usually 0 for released and 1 for pressed) in a single word. This is useful when combinations of key presses are meaningful, and is sometimes used for passing the status of modifier keys on a keyboard (such as shift and control). But it does not scale to support more keys than the number of bits in a single byte or word. For other uses, see Joystick (disambiguation). ...


Devices with many switches (such as a computer keyboard) usually arrange these switches in a scan matrix, with the individual switches on the intersections of x and y lines. When a switch is pressed, it connects the corresponding x and y lines together. Polling (often called scanning in this case) is done by activating each x line in sequence and detecting which y lines then have a signal, thus which keys are pressed. When the keyboard processor detects that a key has changed state, it sends a signal to the CPU indicating the scan code of the key and its new state. The symbol is then encoded, or converted into a number, based on the status of modifier keys and the desired character encoding. A 104-key PC US English QWERTY keyboard layout The Dvorak Simplified Keyboard layout A standard Hebrew keyboard showing both Hebrew and QWERTY. A computer keyboard is a peripheral partially modelled after the typewriter keyboard. ... In communications, a code is a rule for converting a piece of information (for example, a letter, word, or phrase) into another form or representation, not necessarily of the same type. ... A character encoding or character set (sometimes referred to as code page) consists of a code that pairs a sequence of characters from a given set with something else, such as a sequence of natural numbers, octets or electrical pulses, in order to facilitate the storage of text in computers...


Using a custom encoding for a specific application can be done with no loss of data. However, using a standard encoding such as ASCII is problematic if a symbol such as 'ß' needs to be converted but is not in the standard. A character encoding or character set (sometimes referred to as code page) consists of a code that pairs a sequence of characters from a given set with something else, such as a sequence of natural numbers, octets or electrical pulses, in order to facilitate the storage of text in computers... Image:ASCII fullsvg There are 95 printable ASCII characters, numbered 32 to 126. ...


Historical digital systems

Although digital signals are generally associated with the binary electronic digital systems used in modern electronics and computing, digital systems are actually ancient, and need not be binary nor electronic.

  • An abacus is a digital calculator that uses beads on rows to represent numbers. Beads only have meaning in discrete up and down states, not in analog in-between states.
  • A beacon is perhaps the simplest non-electronic digital signal, with just two states (on and off). In particular, smoke signals are one of the oldest examples of a digital signal, where an analog "carrier" (smoke) is modulated with a blanket to generate a digital signal (puffs) that conveys information.
  • DNA comprises a long sequence of four digits (denoted A, C, G, and T), effectively a base-four numeral system. Each of these digits is an organic molecule, known as a nucleotide. DNA is the major system of information transfer from one biological generation to another.
  • Morse code uses six digital states—dot, dash, intra-character gap (between each dot or dash), short gap (between each letter), medium gap (between words), and long gap (between sentences)—to send messages via a variety of potential carriers such as electricity or light, for example using an electrical telegraph or a flashing light.
  • The Braille system was the first binary format for character encoding, using a six-bit code rendered as dot patterns.
  • Semaphore signalling uses rods or flags held in particular positions to send messages to the receiver watching them some distance away.
  • International maritime signal flags have distinctive markings that represent letters of the alphabet to allow ships to send messages to each other.
  • More recently invented, a modem modulates an analog "carrier" signal (such as sound) to encode binary electrical digital information, as a series of binary digital sound pulses. A slightly earlier, surprisingly reliable version of the same concept was to bundle a sequence of audio digital "signal" and "no signal" information (i.e. "sound" and "silence") on magnetic cassette tape for use with early home computers.

It has been suggested that Abax be merged into this article or section. ... This page discusses Beacons, fires designed to attract attention. ... A smoke signal is a form of visual communication used over a long distance, developed both in the Americas and in China. ... For the musical use of modulation, see modulation (music). ... The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ... For the programming language Adenine, see Adenine (programming language). ... Cytosine is one of the 5 main nucleobases used in storing and transporting genetic information within a cell in the nucleic acids DNA and RNA. It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached (an amine group at position 4 and a keto group at... Guanine is one of the five main nucleobases found in the nucleic acids DNA and RNA; the others being adenine, cytosine, thymine, and uracil. ... For the similarly-spelled vitamin compound, see Thiamine Thymine, also known as 5-methyluracil, is a pyrimidine nucleobase. ... A numeral is a symbol or group of symbols, or a word in a natural language that represents a number. ... A nucleotide is a chemical compound that consists of a heterocyclic base, a sugar, and one or more phosphate groups. ... 1922 Chart of the Morse Code Letters and Numerals Morse code is a method for transmitting telegraphic information, using standardized sequences of short and long elements to represent the letters, numerals, punctuation and special characters of a message. ... The electrical telegraph is a telegraph that uses electric signals. ... Braille code where the word (, French for first) can be read. ... A Chappe semaphore tower near Saverne, France // The semaphore or optical telegraph is an apparatus for conveying information by means of visual signals, with towers with pivoting blades or paddles, shutters, in a matrix, or hand-held flags etc. ... The system of international maritime signal flags is a way of representing individual letters of the alphabet in signals to or from ships. ... For other uses, see Modem (disambiguation). ... Typical 60-minute Compact Cassette. ... Children playing on a Amstrad CPC 464 in the 1980s. ...

See also


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NYPL, Digital Library (169 words)
NYPL Digital is your gateway to The Library's rare and unique collections in digitized form.
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digital - a definition from Whatis.com (241 words)
Each of these state digits is referred to as a bit (and a string of bits that a computer can address individually as a group is a byte).
Prior to digital technology, electronic transmission was limited to analog technology, which conveys data as electronic signals of varying frequency or amplitude that are added to carrier waves of a given frequency.
A modem is used to convert the digital information in your computer to analog signals for your phone line and to convert analog phone signals to digital information for your computer.
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