Digital signal are use to storing, processing and communicating information in term of digital form. In digital signal we used discrete steps to represent values and these values are change in discrete time intervals. We also measure the amplitude and time in discrete steps. The digital signal are used in audio, images and speech (signal processing) etc and also in computing communication and data storage, among others. Now a day almost every electronic systems are partially or totally digital based. All real word signals are analog but machines only understand the digital signal. The ability to produce larger and complex system economically makes them excellent for processing and storing information (data).
The dial telephone system is the first digital system. It is design on the basis of switch. A switch can generate two states: open and close. Harvard university built the Harvard mark I in 1939, which is used in operation in 1943. U.S Navy is used the Harvard mark I to compute ballistic tables. After this in research laboratories around the word many more machines were built. In 1944, the ENIAC (Electronic Numerical Integrator and computer) was placed in the Moore school of Electrical Engineering at the University of Pennsylvania, components by components, beginning with the cycling unit and accumulator than this is followed by the initiating unit and function tables in September 1945 and the division and square root unit in October 1945. Finally the primitive computer system is assembler during the fall of 1945.
In 1951, the first commercially produced computer was Univac I. In next decade larger digital computer was introduced. In first generation computer vacuum tubes are used and valves as primary electronic components and were bulky, expensive and consumed immense amount of power. Physicist John Bardeen, Walter Brattain and William Shockley invented a transistor in 1948 at the Bell Telephone Laboratories. Transistors are built on the basis of electrical switches. In electrical switches we use two states: “on” and “off” and they can be used to build the digital circuits and systems. The transistors are firstly used for discrete components but when integrated circuit IC technologies are introduced than their utility increased exponentially. In simple and minimum silicon “chip” a complete digital building block was built due to IC technology. The size of transistor is very small due to this a complete computer is on one chip (microprocessor) and a larger system was integrated into a single chip (system-on-chip).