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# Electronics  # Digital electronics  In many electronic circuits, such as those in radios, the electric current can be of any strength. These circuits are called analogue circuits. In digital circuits, the current can have only two strengths: on and off. Digital circuits are used in a range of devices, including computers, cameras, CD and DVD players and smartphones, in which the flow of electricity is controlled to represent information.

## Binary number system

Numbers are represented in digital circuits using the binary number system. This uses only the digits 0 and 1 and so can easily be represented in electronic circuits by turning currents on or off. In the decimal system (numbers we use in everyday life: 1, 2, 3, etc.), the digits of a number represent ones, tens, hundreds and so on. In the binary system, the digits represent ones, twos, fours, eights and so on. In digital circuits, each 0 or 1 is called a bit. A four-bit binary “word” can represent decimal numbers up to 15 (one 8, one 4, one 2 and one 1). The binary “word” 1101, for example, represents the number 13 (one 8, one 4, no 2s and one 1). So 13 is represented by the four-bit “word” 1101, its digital code. A sequence of eight bits, the number needed to represent a number or letter on a computer, is called a byte.

Almost any sort of information (from simple letters to complex moving images) can be represented by turned into a series of numbers, represented by the digits 0 and 1. This means that any sort of information can be represented in digital electronic circuits by controlling the flow of electricity (0 is for “off” and 1 is for “on”) through it. Computers rely on this fact to store numbers, words, pictures and sounds. They use circuits called logic circuits to process and manipulate the information.  # An hour of music can be stored on a compact disc represented by about 6 billion binary digits. 