Fortran Wiki
FORTRAN 66

Perhaps the most significant development in the early history of FORTRAN was the decision by the American Standards Association (now ANSI) to form a committee to develop an “American Standard Fortran.” The resulting two standards, approved in March 1966, defined two languages, FORTRAN (based on FORTRAN IV, which had served as a de facto standard), and Basic FORTRAN (based on FORTRAN II, but stripped of its machine-dependent features). The FORTRAN defined by the first standard became known as FORTRAN 66 (although many continued to refer to it as FORTRAN IV, the language upon which the standard was largely based). FORTRAN 66 effectively became the first “industry-standard” version of FORTRAN. FORTRAN 66 included:

• Main program, SUBROUTINE, FUNCTION, and BLOCK DATA program units
• INTEGER, REAL, DOUBLE PRECISION, COMPLEX, and LOGICAL data types
• COMMON, DIMENSION, and EQUIVALENCE statements
• DATA statement for specifying initial values
• Intrinsic and EXTERNAL (e.g., library) functions
• Assignment statement
• GOTO, assigned GOTO, and computed GOTO statements
• Logical IF and arithmetic (three-way) IF statements
• DO loops
• READ, WRITE, BACKSPACE, REWIND, and ENDFILE statements for sequential I/O
• FORMAT statement
• CALL, RETURN, PAUSE, and STOP statements
• Hollerith constants in DATA and FORMAT statements, and as actual arguments to procedures
• Identifiers of up to six characters in length
• Comment lines