Fortran (; formerly FORTRAN) is a third-generation, compiled, imperative programming language designed for numeric computation and scientific computing.
Fortran was originally developed by IBM with a reference manual being released in 1956; however, the first compilers only began to produce accurate code two years later. Fortran computer programs have been written to support scientific and engineering applications, such as numerical weather prediction, finite element analysis, computational fluid dynamics, plasma physics, geophysics, computational physics, crystallography and computational chemistry. It is a popular language for high-performance computing and is used for programs that benchmark and rank the world's fastest supercomputers.
Fortran has evolved through numerous versions and dialects. The two most important early versions were FORTRAN II and FORTRAN IV. In 1966, the American National Standards Institute (ANSI) developed a standard for Fortran to limit proliferation of compilers using slightly different syntax. Successive versions have added support for a character data type, structured programming (Fortran 77), array programming, modular programming, generic programming (Fortran 90), parallel computing (Fortran 95), object-oriented programming (Fortran 2003), and concurrent programming (Fortran 2008).
The first manual for FORTRAN describes it as a Formula Translating System, and printed the name with small caps, Fortran. Other sources suggest the name stands for Formula Translator, or, most commonly, Formula Translation.
Early IBM computers did not support lowercase letters, and the names of versions of the language through FORTRAN 77 were usually spelled in all-uppercase. FORTRAN 77 was the last version in which the Fortran character set included only uppercase letters.
The Fortran 90 standard changed the language name from "FORTRAN" with all-caps to "Fortran" with initial caps.
In late 1953, John W. Backus submitted a proposal to his superiors at IBM to develop a more practical alternative to assembly language for programming their IBM 704 mainframe computer. Backus' historic FORTRAN team consisted of programmers Richard Goldberg, Sheldon F. Best, Harlan Herrick, Peter Sheridan, Roy Nutt, Robert Nelson, Irving Ziller, Harold Stern, Lois Haibt, and David Sayre. Its concepts included easier entry of equations into a computer, an idea developed by J. Halcombe Laning and demonstrated in the Laning and Zierler system of 1952. As with other developments in the early days of computing, there were several parallel, independent efforts along these lines, with other instances of proto-Fortran languages including the A-0 System for the UNIVAC I and its follow-on MATH-MATIC, under the direction of Grace Murray Hopper; the high-level language work developed by Heinz Rutishauser for the Zuse 4 computer; and the Mark 1 Autocode work done by R. A. Brooker for the Ferranti Mercury.
A draft specification for The IBM Mathematical Formula Translating System was completed by November 1954. The first manual for FORTRAN appeared in October 1956, with the first FORTRAN compiler delivered in April 1957. Fortran produced efficient enough code for assembly language programmers to accept a high-level programming language replacement.
John Backus said during a 1979 interview with Think, the IBM employee magazine, "Much of my work has come from being lazy. I didn't like writing programs, and so, when I was working on the IBM 701, writing programs for computing missile trajectories, I started work on a programming system to make it easier to write programs."
The language was widely adopted by scientists for writing numerically intensive programs, which encouraged compiler writers to produce compilers that could generate faster and more efficient code. The inclusion of a complex number data type in the language made Fortran especially suited to technical applications such as electrical engineering.
By 1960, versions of FORTRAN were available for the IBM: 709, 650, 1620 and 7090 computers. Significantly, the increasing popularity of FORTRAN spurred competing computer manufacturers to provide FORTRAN compilers for their machines, so that by 1963 over 40 FORTRAN compilers existed. So pervasive was the language within the computing industry that by that time, over 220,000 Fortran manuals of all kinds had been distributed.
FORTRAN was provided for the IBM 1401 computer by an innovative 63-phase compiler that ran entirely in its core memory of only 8000 (six-bit) characters. The compiler could be run from tape, or from a 2200-card deck; it used no further tape or disk storage. It kept the program in memory and loaded overlays that gradually transformed it, in place, into executable form, as described by Haines.
This article was reprinted, edited, in both editions of Anatomy of a Compiler and in the IBM manual "Fortran Specifications and Operating Procedures, IBM 1401". The executable form was not entirely machine language; rather, floating-point arithmetic, sub-scripting, input/output, and function references were interpreted, preceding UCSD Pascal P-code by two decades. GOTRAN, a simplified, interpreted version of FORTRAN I (with only 12 types of statements not 32) for "load and go" operation was available (at least for the early IBM 1620 computer). Modern Fortran, and almost all later versions, are fully compiled, as done for other high-performance languages.
The development of Fortran paralleled the early evolution of compiler technology, and many advances in the theory and design of compilers were specifically motivated by the need to generate efficient code for Fortran programs. Indeed, the Fortran compiler was one of the most complicated programs of any kind in existence at the time, and it was used by IBM's Product Test group in Poughkeepsie, New York, as part of acceptance testing for newly built computers.
The initial release of FORTRAN for the IBM 704 contained 32 types of statements, including:
DIMENSION and EQUIVALENCE statements
Three-way arithmetic IF statement (since deprecated), which passed control to one of three locations in the program depending on whether the result of the arithmetic expression was negative, zero, or positive
Control statements for checking exceptions (IF ACCUMULATOR OVERFLOW, IF QUOTIENT OVERFLOW, and IF DIVIDE CHECK); and control statements for manipulating sense switches and sense lights (IF (SENSE SWITCH), IF (SENSE LIGHT), and SENSE LIGHT)