A compiler is a program that takes source code written in a language meant for people and translates it into the low-level machine instructions a particular computer can execute. The programmer writes once in the higher-level language, and the compiler produces a machine-language version that runs on the hardware.
Before high-level languages, programs were typically written directly in machine or assembly language, tied to one computer and tedious to write and change. The promise of a compiler is to let people work in a clearer, more portable notation while a tool handles the detailed translation into instructions the machine understands.
FORTRAN, released for the IBM 704 in 1957, was a landmark in showing that this approach could be efficient. According to the 1957 paper “The FORTRAN Automatic Coding System,” the team built a translator that did extensive analysis of arithmetic, indexing, and loop structure so that its output ran nearly as fast as hand-written machine code. The FORTRAN Programmer’s Reference Manual presents the language in algebra-like notation while the system handles the translation to the 704’s instructions.
That result mattered because many programmers had assumed automatic translation would always produce slow code. By proving a compiler could generate efficient programs, FORTRAN helped establish high-level languages and compilation as the normal way to write software, a model that nearly all later languages followed.