Digital systems


The concept of digital computer soars to Charles Babbage (1791-1871), who developed a difference engine about 1830.

Photograph of Charles Babbage in 1847.

Difference Engine (Science Museum, London).

The first digital computer was developed in 1944, at Harvard University, but it was electromechanic, not electronic. The modern digital electronic began in 1946 with the digital electronic computer ENIAC (Electronic Numerical Integrator and Computer), it was built at the University of Pennsylvania's Moore School of Electrical Engineering. Its birth lay in World War II as a classified military project known only as Project PX. Built out of some 17,468 electronic vacuum tubes, ENIAC was in its time the largest single electronic apparatus in the world.

The ENIAC computer, 1946.

The digital term refers to the way computers do operations : counting digits. Nowadays, digital technology has application in a wide variety of areas, such as telephonic systems, radar, navigation systems, medical instrumentation, etc. Digital technology has progressed from the vacuum tubes circuits to integrated circuits and microprocessors.

Combinational and sequential logic

The output of combinational logic circuits depends only on their inputs' state. Sequential circuits are more general than combinational logic circuits, because their ouput at time t depends also on the past inputs.


The following are some examples of specification and implementation of some combinational and sequential circuits :

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