Generally the word ‘digit’ means number. The word ‘digital’ comes from the word digit. Digital signal means such a communicative signal which can receive some definite value. These can be changed into discrete values and each of them can be identified separately. In this system, with the help of binary code i.e. 0 and 1, any information, number, letter or any special signal etc. can be understood or sent. In this signal system, the value of ‘on’ state is 1 and the value of ‘off’ state is 0.
Figure: transformation of analogue signal to a digital signal
Computer saves, process and sends any data as digital signal. With help of modem, analogue data can be changed into digital and digital data can be changed into analogue data. Analogue clock shows the time by continuous rotation of the hands and digital clock gives the time by changing the digits.
Common practical digital signals are represented as 8-bit (256 levels), 16-bit (65,536 levels), 32-bit (4.3 billion levels). But the number of quantization levels is not limited to powers of two.