Computers

Electronic computers are divided into four generations: 1st on vacuum tubes (1946–1955), 2nd on transistors (1956–1965), 3rd on integrated circuits (1966–1974) and 4th on large-scale integrated circuits and microprocessors (from 1975). The transistor was made in 1947 at Bell Laboratories by Shockley, Bardeen and Brattain (Nobel Prize 1956); it sharply reduced the size and power use of machines. A computer is a universal automatic device that processes information at high speed under a program. Its main devices are the system unit, monitor and keyboard; additional devices include the mouse, printer, scanner, webcam and others. The system unit holds the motherboard, processor, memory and power supply. The processor performs arithmetic and logic operations and controls the other devices; its performance depends on clock frequency (GHz), bit width and number of cores. RAM holds programs and data while the computer works and loses them when power is off; ROM keeps the start-up program (BIOS/UEFI) that runs when the computer is switched on. 8 bits = 1 byte; an address bus of n bits can express 2ⁿ addresses.