This article is about the concept in information theory and information systems. For the electronics concept, see Digital signal. For other uses, see Digital.
Digital data, in information theory and information systems, is information represented as a string of discrete symbols, each of which can take on one of only a finite number of values from some alphabet, such as letters or digits. An example is a text document, which consists of a string of alphanumeric characters. The most common form of digital data in modern information systems is binary data, which is represented by a string of binary digits (bits) each of which can have one of two values, either 0 or 1.
Digital clock. The time shown by the digits on the face at any instant is digital data. The actual precise time is analog data.
Digital data can be contrasted with analog data, which is represented by a value from a continuous range of real numbers. Analog data is transmitted by an analog signal, which not only takes on continuous values but can vary continuously with time, a continuous real-valued function of time. An example is the air pressure variation in a sound wave.
The word digital comes from the same source as the words digit and digitus (the Latin word for finger), as fingers are often used for counting. Mathematician George Stibitz of Bell Telephone Laboratories used the word digital in reference to the fast electric pulses emitted by a device designed to aim and fire anti-aircraft guns in 1942.[1] The term 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.
A symbol input device usually consists of a group of switches that are polled at regular intervals to see which switches are switched. 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 typically sends an interrupt, in a specialized format, so that the CPU can read it.
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.
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 custom encoding can be used for a specific application 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.
It is estimated that in the year 1986 less than 1% of the world's technological capacity to store information was digital and in 2007 it was already 94%.[2] The year 2002 is assumed to be the year when humankind was able to store more information in digital than in analog format (the "beginning of the digital age").[3][4]
All digital information possesses common properties that distinguish it from analog data with respect to communications:
Synchronization: Since digital information is conveyed by the sequence in which symbols are ordered, all digital schemes have some method for determining the beginning of a sequence. In written or spoken human languages, synchronization is typically provided by pauses (spaces), capitalization, and punctuation. Machine communications typically use special synchronization sequences.
Language: All digital communications require a formal language, which in this context consists of all the information that the sender and receiver of the digital communication must both possess, in advance, for the communication to be successful. Languages are generally arbitrary and specify the meaning to be assigned to particular symbol sequences, the allowed range of values, methods to be used for synchronization, etc.
Errors: Disturbances (noise) in analog communications invariably introduce some, generally small deviation or error between the intended and actual communication. Disturbances in digital communication only result in errors when the disturbance is so large as to result in a symbol being misinterpreted as another symbol or disturbing the sequence of symbols. It is generally possible to have near-error-free digital communication. Further, techniques such as check codes may be used to detect errors and correct them through redundancy or re-transmission. Errors in digital communications can take the form of substitution errors in which a symbol is replaced by another symbol, or insertion/deletion errors in which an extra incorrect symbol is inserted into or deleted from a digital message. Uncorrected errors in digital communications have an unpredictable and generally large impact on the information content of the communication.
Copying: Because of the inevitable presence of noise, making many successive copies of an analog communication is infeasible because each generation increases the noise. Because digital communications are generally error-free, copies of copies can be made indefinitely.
Granularity: The digital representation of a continuously variable analog value typically involves a selection of the number of symbols to be assigned to that value. The number of symbols determines the precision or resolution of the resulting datum. The difference between the actual analog value and the digital representation is known as quantization error. For example, if the actual temperature is 23.234456544453 degrees, but only two digits (23) are assigned to this parameter in a particular digital representation, the quantizing error is 0.234456544453. This property of digital communication is known as granularity.
Compressible: According to Miller, "Uncompressed digital data is very large, and in its raw form, it would actually produce a larger signal (therefore be more difficult to transfer) than analog data. However, digital data can be compressed. Compression reduces the amount of bandwidth space needed to send information. Data can be compressed, sent, and then decompressed at the site of consumption. This makes it possible to send much more information and results in, for example, digital television signals offering more room on the airwave spectrum for more television channels."[4]
Historical digital systems
Even though 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 or electronic.
DNAgenetic code is a naturally occurring form of digital data storage.
Written text (due to the limited character set and the use of discrete symbols – the alphabet in most cases)
The abacus was created sometime between 1000 BC and 500 BC, it later became a form of calculation frequency. Nowadays it can be used as a very advanced, yet basic 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.
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 uses a six-bit code rendered as dot patterns.
Flag semaphore 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.
^Hilbert, Martin; López, Priscila (April 2011). "The World's Technological Capacity to Store, Communicate, and Compute Information". Science. 332 (6025): 60–65. Bibcode:2011Sci...332...60H. doi:10.1126/science.1200970. ISSN 0036-8075. PMID 21310967. S2CID 206531385.
^""video animation on The World's Technological Capacity to Store, Communicate, and Compute Information from 1986 to 2010" – via YouTube.
^ abMiller, Vincent (2011). Understanding digital culture. London: Sage Publications. sec. "Convergence and the contemporary media experience". ISBN978-1-84787-497-9.
^"The three states of information". The University of Edinburgh. Retrieved 21 February 2021.
Further reading
Tocci, R. 2006. Digital Systems: Principles and Applications (10th Edition). Prentice Hall. ISBN0-13-172579-3
March 10, 2023
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This article is about the concept in information theory and information systems For the electronics concept see Digital signal For other uses see Digital Digital data in information theory and information systems is information represented as a string of discrete symbols each of which can take on one of only a finite number of values from some alphabet such as letters or digits An example is a text document which consists of a string of alphanumeric characters The most common form of digital data in modern information systems is binary data which is represented by a string of binary digits bits each of which can have one of two values either 0 or 1 Digital clock The time shown by the digits on the face at any instant is digital data The actual precise time is analog data Digital data can be contrasted with analog data which is represented by a value from a continuous range of real numbers Analog data is transmitted by an analog signal which not only takes on continuous values but can vary continuously with time a continuous real valued function of time An example is the air pressure variation in a sound wave The word digital comes from the same source as the words digit and digitus the Latin word for finger as fingers are often used for counting Mathematician George Stibitz of Bell Telephone Laboratories used the word digital in reference to the fast electric pulses emitted by a device designed to aim and fire anti aircraft guns in 1942 1 The term 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 Contents 1 Symbol to digital conversion 2 States 3 Properties of digital information 4 Historical digital systems 5 See also 6 References 7 Further readingSymbol to digital conversion EditThis section possibly contains original research Please improve it by verifying the claims made and adding inline citations Statements consisting only of original research should be removed August 2016 Learn how and when to remove this template message Since symbols for example alphanumeric characters are not continuous representing symbols digitally is rather simpler than conversion of continuous or analog information to digital Instead of sampling and quantization as in analog to digital conversion such techniques as polling and encoding are used A symbol input device usually consists of a group of switches that are polled at regular intervals to see which switches are switched 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 typically sends an interrupt in a specialized format so that the CPU can read it 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 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 custom encoding can be used for a specific application 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 It is estimated that in the year 1986 less than 1 of the world s technological capacity to store information was digital and in 2007 it was already 94 2 The year 2002 is assumed to be the year when humankind was able to store more information in digital than in analog format the beginning of the digital age 3 4 States EditDigital data come in these three states data at rest data in transit and data in use The confidentiality integrity and availability have to be managed during the entire lifecycle from birth to the destruction of the data 5 Properties of digital information EditAll digital information possesses common properties that distinguish it from analog data with respect to communications Synchronization Since digital information is conveyed by the sequence in which symbols are ordered all digital schemes have some method for determining the beginning of a sequence In written or spoken human languages synchronization is typically provided by pauses spaces capitalization and punctuation Machine communications typically use special synchronization sequences Language All digital communications require a formal language which in this context consists of all the information that the sender and receiver of the digital communication must both possess in advance for the communication to be successful Languages are generally arbitrary and specify the meaning to be assigned to particular symbol sequences the allowed range of values methods to be used for synchronization etc Errors Disturbances noise in analog communications invariably introduce some generally small deviation or error between the intended and actual communication Disturbances in digital communication only result in errors when the disturbance is so large as to result in a symbol being misinterpreted as another symbol or disturbing the sequence of symbols It is generally possible to have near error free digital communication Further techniques such as check codes may be used to detect errors and correct them through redundancy or re transmission Errors in digital communications can take the form of substitution errors in which a symbol is replaced by another symbol or insertion deletion errors in which an extra incorrect symbol is inserted into or deleted from a digital message Uncorrected errors in digital communications have an unpredictable and generally large impact on the information content of the communication Copying Because of the inevitable presence of noise making many successive copies of an analog communication is infeasible because each generation increases the noise Because digital communications are generally error free copies of copies can be made indefinitely Granularity The digital representation of a continuously variable analog value typically involves a selection of the number of symbols to be assigned to that value The number of symbols determines the precision or resolution of the resulting datum The difference between the actual analog value and the digital representation is known as quantization error For example if the actual temperature is 23 234456544453 degrees but only two digits 23 are assigned to this parameter in a particular digital representation the quantizing error is 0 234456544453 This property of digital communication is known as granularity Compressible According to Miller Uncompressed digital data is very large and in its raw form it would actually produce a larger signal therefore be more difficult to transfer than analog data However digital data can be compressed Compression reduces the amount of bandwidth space needed to send information Data can be compressed sent and then decompressed at the site of consumption This makes it possible to send much more information and results in for example digital television signals offering more room on the airwave spectrum for more television channels 4 Historical digital systems EditEven though 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 or electronic DNA genetic code is a naturally occurring form of digital data storage Written text due to the limited character set and the use of discrete symbols the alphabet in most cases The abacus was created sometime between 1000 BC and 500 BC it later became a form of calculation frequency Nowadays it can be used as a very advanced yet basic 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 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 uses a six bit code rendered as dot patterns Flag semaphore 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 See also EditAnalog to digital converter Barker code Binary number Comparison of analog and digital recording Data computer science Data remanence Digital architecture Digital art Digital control Digital divide Digital electronics Digital infinity Digital native Digital physics Digital recording Digital Revolution Digital video Digital to analog converter Internet forumReferences Edit Ceruzzi Paul E 29 June 2012 Computing A Concise History MIT Press ISBN 978 0 262 51767 6 Hilbert Martin Lopez Priscila April 2011 The World s Technological Capacity to Store Communicate and Compute Information Science 332 6025 60 65 Bibcode 2011Sci 332 60H doi 10 1126 science 1200970 ISSN 0036 8075 PMID 21310967 S2CID 206531385 video animation on The World s Technological Capacity to Store Communicate and Compute Information from 1986 to 2010 via YouTube a b Miller Vincent 2011 Understanding digital culture London Sage Publications sec Convergence and the contemporary media experience ISBN 978 1 84787 497 9 The three states of information The University of Edinburgh Retrieved 21 February 2021 Further reading EditTocci R 2006 Digital Systems Principles and Applications 10th Edition Prentice Hall ISBN 0 13 172579 3 Retrieved from https en wikipedia org w index php title Digital data amp oldid 1133163235, wikipedia, wiki, book, books, library,
