Abstract Recent progress in metal-oxide semiconductor (MOS) large-scale integration (LSI) technology has yielded a new type of component, the microcomputer, or “computer-on-a-chip”. Its impact is already proving to be spectacular. The term of microprocessor has been heretofore reserved for microprogrammable processors. A new meaning has been introduced, and is now widely accepted: the word “microprocessor” designates here an MOS-LSI processor equipped with CPU-like functions. “Micro” is then a reference to the size. This does not refer to the control philosophy used in the processor design: a microprocessor is not necessarily microprogrammed. Other LSI processors, equipped with only minimal arithmetic functions (4 to 8 functions) are designated as calculators. The main characteristic of an LSI MOS “chip” (silicon semiconductor die) is to achieve very high interconnect and logic density in a minute volume. Recent memories implement a 4K bit RAM in a single chip. The resulting advantages are economy and performance: low cost, size, weight, and power consumption, high reliability, logic complexity, and speed. The principal limitation is in speed which is currently lower than bipolar. Microprocessors represent a natural evolution from calculator chips, and were first introduced by Intel in 1971. Most major companies are now in the process of producing microprocessor systems. After an overview of MOS LSI technology, possible microprocessor organizations are analyzed. The main microprocessors currently available, or due to be introduced, are presented. Finally, applications of microcomputer systems are surveyed, and their impact is evaluated.