A digital system uses discrete (that is, discontinuous) values to represent information for input, processing, transmission, storage, etc. By contrast, non-digital (or analog) systems use a continuous range of values to represent information. An analog or analogue signal is any continuous signal for which the time varying feature (variable of the signal is a representation of some other In Mathematics, the word continuum has at least two distinct meanings outlined in the sections below Although digital representations are discrete, the information represented can be either discrete, such as numbers, letters or icons, or continuous, such as sounds, images, and other measurements of continuous systems. A number is an Abstract object, tokens of which are Symbols used in Counting and measuring. A letter is an element in an Alphabetic system of writing such as the Greek alphabet and its descendants An icon (from Greek εἰκών eikōn, "image" is a religious work of art most commonly a painting from Eastern Christianity.

The word digital comes from the same source as the word digit and digitus (the Latin word for finger), as fingers are used for discrete counting. Latin ( lingua Latīna, laˈtiːna is an Italic language, historically spoken in Latium and Ancient Rome. A finger is a type of digit, an organ of manipulation and sensation found in the Hands of Humans and other Primates Normally humans have five digits

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. Computing is usually defined like the activity of using and developing Computer technology Computer hardware and software. Electronics refers to the flow of charge (moving Electrons through Nonmetal conductors (mainly Semiconductors, whereas electrical 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 uses Digital signals for Sound reproduction. This includes analog-to-digital conversion, digital-to-analog conversion, storage Digital photography is a form of Photography that utilizes Digital technology to make Digital images of subjects Such data-carrying signals carry electronic or optical pulses, the amplitude of each of which represents a logical 1 (pulse present and/or high) or a logical 0 (pulse absent and/or low).

## Digital noise

When data are transmitted, or indeed handled at all, a certain amount of noise enters into the signal. is a one volume manga created by Tsutomu Nihei as a prequel to his ten-volume work Blame!. Noise can have several causes: data transmitted wirelessly, such as by radio, may be received inaccurately, suffer interference from other wireless sources, or pick up background noise from the rest of the universe. Radio is the transmission of signals by Modulation of electromagnetic waves with frequencies below those of visible Light. In physics interference is the addition ( superposition) of two or more Waves that result in a new wave pattern Microphones pick up both the intended signal as well as background noise without discriminating between signal and noise, so when audio is encoded digitally, it typically already includes noise. ELO.

Electric pulses transmitted via wires are typically 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 provide 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 (e. g. , alphanumeric characters) are not continuous, converting symbols to digital form is rather simpler and less prone to data loss than analog to digital conversion. Alphanumeric is a is Portmanteau of Alphabetic and Numeric and is used to describe the collection of Latin letters and Arabic digits For other uses see Character. In Computer and machine-based Telecommunications terminology a character is a unit of Instead of sampling and quantization as in D/A (digital-to-analog) conversion, such techniques as polling and encoding are used. Polling, or polled operation in Computer science, refers to actively sampling the status of an external device by a client program as a synchronous activity A character encoding consists of a code that pairs a sequence of characters from a given character set (sometimes incorrectly referred to as Code page

A symbol input device usually consists of a number of switches that 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 typically sends an interrupt to alert the CPU to read it. In Computing, an interrupt is an asynchronous signal from hardware indicating the need for attention or a synchronous event in software indicating the need for a change

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. A joystick is an input device consisting of a stick that pivots on a base and reports its angle or direction to the device it is controlling 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. In Computing, a keyboard is an Input device partially modelled after the typewriter keyboard which uses an arrangement of buttons or keys 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. In Communications a code is a rule for converting a piece of Information (for example a letter, Word, Phrase, or A character encoding consists of a code that pairs a sequence of characters from a given character set (sometimes incorrectly referred to as Code page

A custom encoding can be used for a specific application with no loss of data. A character encoding consists of a code that pairs a sequence of characters from a given character set (sometimes incorrectly referred to as Code page 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. American Standard Code for Information Interchange ( ASCII)

## 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 was created sometime between 1,000 BC and 500 BC , it later become 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. An abacus, also called a counting frame, is a calculating tool used primarily by Asians for performing arithmetic processes 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). Beacons are aids to Navigation devices Intentionally conspicuous beacons help guide navigators to their destinations 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. The smoke signal is one of the oldest forms of communication in recorded history In Telecommunications, modulation is the process of varying a periodic Waveform, i
• DNA comprises a long sequence of four digits (denoted A, C, G, and T), effectively a base-four numeral system. Deoxyribonucleic acid ( DNA) is a Nucleic acid that contains the genetic instructions used in the development and functioning of all known Adenine is a Purine with a variety of roles in Biochemistry including Cellular respiration, in the form of both the energy-rich Adenosine Cytosine is one of the five main bases found in DNA and RNA. It is a Pyrimidine derivative with a Heterocyclic Aromatic ring Guanine is one of the five main Nucleobases found in the Nucleic acids DNA and RNA, the others being Adenine, Cytosine, Thymine is one of the four bases in the Nucleic acid of DNA that make up the letters ATGC A numeral system (or system of numeration) is a Mathematical notation for representing numbers of a given set by symbols in a consistent manner Each of these digits is an organic molecule, known as a nucleotide. Nucleotides are Organic compounds that consist of three joined structures a nitrogenous base a Sugar, and a Phosphate group 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. Morse code is a Character encoding for transmitting telegraphic information using standardized sequences of short and long elements to represent the letters numerals The electrical telegraph is a telegraph that uses electric signals The electromagnetic telegraph is a device for human-to-human transmission
• The Braille system was the first binary format for character encoding, using a six-bit code rendered as dot patterns. The Braille system is a method that is widely used by blind people to read and write
• Flag semaphore uses rods or flags held in particular positions to send messages to the receiver watching them some distance away. Flag semaphore is a system for conveying information at a distance by means of visual signals with hand-held flags rods disks paddles or occasionally bare or gloved hands
• 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. Modem (from mo dulator- dem odulator is a device that modulates an analog carrier signal to encode Digital information 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. The Compact Cassette, often referred to as audio cassette, cassette tape, cassette, or simply tape, is a Magnetic tape sound A home computer was a class of Personal computer entering the market in 1977 and becoming common during the 1980s

Analog sound versus digital sound compares the two ways in which Sound is recorded and stored An analog-to-digital converter (abbreviated ADC, A/D or A to D) is an electronic integrated circuit which converts continuous signals to Digital art most commonly refers to Art created on a Computer in Digital form Digital control is a branch of Control theory that uses Digital Computers to act as a system Information Age is a term that has been used to refer to the present era Digital electronics are Electronics systems that use Digital signals Digital electronics are representations of Boolean algebra also see A digital native is a person who has grown up with Digital technology such as Computers the Internet, Mobile phones and MP3. Digital physics holds the basic premise that the entire history of our Universe is Computable, that is the output of a (presumably short computer program This article presents a Timeline of events in the history of Computing from 1990 to the present The term digital signal is used to refer to more than one concept