PDP-X FORTRAN IV Initial Specifications

This document, dated October 14, 1967, details the initial specifications for the FORTRAN IV language as implemented on the Digital Equipment Corporation (DEC) PDP-X computer. The memorandum is directed toward systems programmers tasked with building the compiler.

Key aspects of the document include:

• Language Structure: Defines card and paper tape formats, including conventions for statement numbers, continuation fields, and comments.
• Data Elements: Covers variable naming conventions (1-6 alphanumeric characters starting with a letter), data types (integer, real, double precision, logical), and array handling (up to 3 dimensions).
• Expressions: Outlines the rules for constructing arithmetic and logical expressions, including operator precedence.
• Control Statements: Specifies the syntax for flow-control statements, including various forms of GO TO, IF statements (arithmetic and logical), and DO loops.
• Input/Output and Formatting: Describes the I/O statement architecture and provides detailed specifications for FORMAT statements, including I, E, F, D, P, L, A, H, X, and O field descriptors.
• Subprograms: Outlines the five categories of subprograms: statement functions, intrinsic functions, external functions, subroutines, and block data subprograms.
• Compatibility: An appendix notes differences between the proposed PDP-X FORTRAN and existing ASA (American Standards Association) standards, as well as its relationship to the PDP-9 FORTRAN manual.