FORTRAN IV Language Manual PDP-9 Advanced System Software

This manual describes the FORTRAN IV programming language as implemented for the PDP-9 computer, providing essential information for users to write, compile, and execute FORTRAN programs within the PDP-9 Advanced Software System.

It covers the fundamental elements of the FORTRAN language, including:

• Constants and Variables: Defining integer, real, double-precision, logical, and Hollerith constants, along with rules for naming and typing variables.
• Arrays and Subscripts: How to declare, store, and reference data in one, two, and three-dimensional arrays.
• Expressions: Rules for constructing arithmetic, relational, and logical expressions, including operator hierarchy and data type modes.
• Statements: Detailed explanations of arithmetic assignment statements, control flow statements (e.g., GO TO, IF, DO, PAUSE, STOP, END), and input/output (I/O) statements (READ, WRITE) for data transfer.
• FORMAT Statements: Specifies how data is converted between internal machine language and external notation for various data types (integer, floating-point, alphanumeric, logical, etc.).
• Specification Statements: Defines variables, allocates storage, and initializes data through statements like TYPE, DIMENSION, COMMON, EQUIVALENCE, EXTERNAL, and DATA.
• Subprograms: Describes the use and structure of Statement Functions, Intrinsic/Library Functions, External Functions, Subroutines, and BLOCK DATA subprograms for modular programming and data initialization.

The document notes that this PDP-9 FORTRAN IV implementation largely adheres to the USA Standard FORTRAN (X3.9-1966) but includes specific modifications to operate within 8192 words of core storage, such as the exclusion of complex arithmetic, non-adjustable array sizes in subprograms, treating blank COMMON as named COMMON, and disallowing implied DO in DATA statements.