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a computer program by which a high-level programming language, such as COBOL or FORTRAN, is converted into machine language that can be acted upon by a computer


(computer science)
A program to translate a higher programming language into machine language. Also known as compiling routine.


(programming, tool)
A program that converts another program from some source language (or programming language) to machine language (object code). Some compilers output assembly language which is then converted to machine language by a separate assembler.

A compiler is distinguished from an assembler by the fact that each input statement does not, in general, correspond to a single machine instruction or fixed sequence of instructions. A compiler may support such features as automatic allocation of variables, arbitrary arithmetic expressions, control structures such as FOR and WHILE loops, variable scope, input/ouput operations, higher-order functions and portability of source code.

AUTOCODER, written in 1952, was possibly the first primitive compiler. Laning and Zierler's compiler, written in 1953-1954, was possibly the first true working algebraic compiler.

See also byte-code compiler, native compiler, optimising compiler.


(1) Software that converts a set of high-level language statements into a lower-level representation. For example, a help compiler converts a text document embedded with appropriate commands into an online help system. A dictionary compiler converts terms and definitions into a dictionary lookup system.

(2) Software that translates a program written in a high-level programming language (C/C++, COBOL, etc.) into machine language. A compiler usually generates assembly language first and then translates the assembly language into machine language. A utility known as a "linker" then combines all required machine language modules into an executable program that can run in the computer. See optimizing compiler.

The following is a conceptual example of source code being converted to assembly language and machine code by the compiler:

Source Code

  Assembly Language  Machine Language
  Compare A to B     Compare 3477 2883
  If equal go to C   If = go to 23732
  Go to D            Go to 23119

  Machine Code

From C to Assembly Language
A C/C++ compiler converts C and C++ code into assembly language as shown in this example. The red arrows point to various function calls, and the assembly code to perform those calls follows each statement.

Compilers and Interpreters
Compiled programs (right) are translated into the machine language of the target computer. Interpreted programs (left and center) are either kept in their original source code or are precompiled into an intermediate form. In both cases, an interpreter is required to translate the program into machine language at runtime, whereas the compiled program is "ready to go."