PDP-11 FORTRAN IV Language Reference Manual

This document serves as a comprehensive reference manual for the PDP-11 FORTRAN IV language, detailing its elements as implemented for PDP-11 systems as of March 1983. Based on American National Standard (ANS) FORTRAN X3.9-1966, it highlights numerous enhancements specific to PDP-11, including extended capabilities for array subscripts, mixed-mode expressions, and a LOGICAL*1 data type.

The manual is structured into nine chapters and two appendices, covering:

• Language Fundamentals: General information on FORTRAN programs, including character set, line formatting (character-per-column and tab-character), statement labels, comments, debugging statements, and overall program unit structure.
• Statement Components: Detailed descriptions of symbolic names, various data types (Integer, Real, Double Precision, Complex, Logical, Hollerith, and Alphanumeric Literals), constants, variables, and arrays (declarators, subscripts, storage, and adjustable arrays). It also explains how data types are specified and the structure of arithmetic, relational, and logical expressions.
• Program Control: Assignment statements (arithmetic, logical, and ASSIGN) and control statements (GO TO, IF, DO loops, CONTINUE, CALL, RETURN, PAUSE, STOP, and END) that manage program flow, iteration, and termination.
• Data Definition & Allocation: Specification statements like IMPLICIT, TYPE DECLARATION, DIMENSION, COMMON, VIRTUAL (for large data areas outside normal program space), EQUIVALENCE, EXTERNAL, DATA, PROGRAM, and BLOCK DATA, which define the characteristics of program entities and memory allocation.
• Subprograms: User-written subprograms (statement functions, function subprograms, and subroutine subprograms) and FORTRAN library functions, including rules for arguments and function references.
• Input/Output (I/O): A thorough overview of I/O statements (READ, ACCEPT, WRITE, REWRITE, TYPE, PRINT, FIND, ENCODE, DECODE) for formatted and unformatted data transfer, covering sequential, direct access, and in-memory operations. It explains I/O list components, records, files, and access modes.
• FORMAT Statements: Dedicated section on FORMAT statements for specifying data editing and formatting, including various field descriptors (I, O, F, E, D, G, L, A, H, X, T, P, Q, $, :), carriage control characters, format separators, and run-time formats.
• Auxiliary I/O Statements: File management functions such as OPEN (with extensive keyword options for file attributes), CLOSE, REWIND, BACKSPACE, ENDFILE, and DEFINE FILE.
• Appendices: Summaries of the FORTRAN, ASCII, and RADIX-50 character sets, expression operators, and FORTRAN IV library functions.

The manual is intended for readers who already possess a basic understanding of FORTRAN, serving as a comprehensive technical guide rather than a tutorial.