Computer program

A computer program is a collection of instructions that performs a specific task when executed by a computer. Most computer devices require programs to function properly. A computer program is a collection of instructions that performs a specific task when executed by a computer. Most computer devices require programs to function properly. A computer program is usually written by a computer programmer in a programming language. From the program in its human-readable form of source code, a compiler or assembler can derive machine code—a form consisting of instructions that the computer can directly execute. Alternatively, a computer program may be executed with the aid of an interpreter. A collection of computer programs, libraries, and related data are referred to as software. Computer programs may be categorized along functional lines, such as application software and system software. The underlying method used for some calculation or manipulation is known as an algorithm. The earliest programmable machines preceded the invention of the digital computer. As early as the 9th century, a programmable music sequencer was invented by the Persian Banu Musa brothers, who described an automated mechanical flute player in the Book of Ingenious Devices. In 1206, the Arab engineer Al-Jazari invented a programmable drum machine where musical mechanical automata could be made to play different rhythms and drum patterns. In 1801, Joseph-Marie Jacquard devised a loom that would weave a pattern by following a series of perforated cards. Patterns could be woven and repeated by arranging the cards. In 1837, Charles Babbage was inspired by Jacquard's loom to attempt to build the Analytical Engine.The names of the components of the calculating device were borrowed from the textile industry. In the textile industry, yarn was brought from the store to be milled. The device would have had a 'store'—memory to hold 1,000 numbers of 40 decimal digits each. Numbers from the 'store' would then have then been transferred to the 'mill' (analogous to the CPU of a modern machine), for processing. And a 'thread' being the execution of programmed instructions by the device. It was programmed using two sets of perforated cards—one to direct the operation and the other for the input variables. However, after more than 17,000 pounds of the British government's money, the thousands of cogged wheels and gears never fully worked together. During a nine-month period in 1842–43, Ada Lovelace translated the memoir of Italian mathematician Luigi Menabrea. The memoir covered the Analytical Engine. The translation contained Note G which completely detailed a method for calculating Bernoulli numbers using the Analytical Engine. This note is recognized by some historians as the world's first written computer program. In 1936, Alan Turing introduced the Universal Turing machine—a theoretical device that can model every computation that can be performed on a Turing complete computing machine.It is a finite-state machine that has an infinitely long read/write tape. The machine can move the tape back and forth, changing its contents as it performs an algorithm. The machine starts in the initial state, goes through a sequence of steps, and halts when it encounters the halt state.This machine is considered by some to be the origin of the stored-program computer—used by John von Neumann (1946) for the 'Electronic Computing Instrument' that now bears the von Neumann architecture name. The Z3 computer, invented by Konrad Zuse (1941) in Germany, was a digital and programmable computer. A digital computer uses electricity as the calculating component. The Z3 contained 2,400 relays to create the circuits. The circuits provided a binary, floating-point, nine-instruction computer. Programming the Z3 was through a specially designed keyboard and punched tape. The Electronic Numerical Integrator And Computer (Fall 1945) was a Turing complete, general-purpose computer that used 17,468 vacuum tubes to create the circuits. At its core, it was a series of Pascalines wired together. Its 40 units weighed 30 tons, occupied 1,800 square feet (167 m2), and consumed $650 per hour (in 1940s currency) in electricity when idle. It had 20 base-10 accumulators. Programming the ENIAC took up to two months. Three function tables were on wheels and needed to be rolled to fixed function panels. Function tables were connected to function panels using heavy black cables. Each function table had 728 rotating knobs. Programming the ENIAC also involved setting some of the 3,000 switches. Debugging a program took a week. The programmers of the ENIAC were women who were known collectively as the 'ENIAC girls.' The ENIAC featured parallel operations. Different sets of accumulators could simultaneously work on different algorithms. It used punched card machines for input and output, and it was controlled with a clock signal. It ran for eight years, calculating hydrogen bomb parameters, predicting weather patterns, and producing firing tables to aim artillery guns.