PDP-7 FORTRAN II

This document serves as a comprehensive programming manual for the FORTRAN II system on the PDP-7 computer, published in 1966. It is designed as a reference guide for programmers already familiar with general FORTRAN II concepts, detailing the language, its components, and operating procedures specifically for the PDP-7, particularly for systems utilizing paper tape.

The manual covers the following key areas:

1. FORTRAN II Language Fundamentals: Introduces the structure of FORTRAN II programs, including arithmetic, program control, data specification, and input/output statements. It describes how to prepare programs with identification fields (for statement numbers, comments, symbolic machine instructions, and line continuation) and statement fields.
2. Data Representation and Variables: Explains how numbers are represented as either integers (fixed-point, 18-bit) or real numbers (floating-point with an exponent and mantissa, available in two- or three-word storage modes). It outlines variable naming conventions and the use of DIMENSION statements to declare arrays and their maximum sizes.
3. Arithmetic Statements and Expressions: Details the formation of arithmetic expressions using constants, variables, functions, and operators, specifying the order of evaluation and the role of parentheses. It also explains mixed-mode computation and the handling of internal arithmetic statements.
4. Program Control: Describes statements for altering program flow, such as GOTO (unconditional, computed, and assigned), IF for conditional branching, and DO loops for iteration. It also covers CONTINUE for loop termination and STOP and PAUSE for program termination or temporary suspension.
5. Input/Output Operations: Provides instructions for READ and WRITE statements, including specifying I/O devices, data lists, and FORMAT statements to define data arrangement. Various data field formats (I, F, E for numeric; X, H, A for non-numeric) are explained, along with multi-record formatting and specific I/O procedures for devices like paper tape, keyboard, magnetic tape, and DECtape.
6. Subprograms (Functions and Subroutines): Differentiates between FUNCTION subprograms (which return a single value) and SUBROUTINE subprograms (which perform operations and can return multiple results). It details argument passing, the use of RETURN statements, and the COMMON statement for sharing data between programs.
7. Machine Language Interface: Explains how to integrate symbolic machine instructions directly into FORTRAN programs and discusses the conventions the compiler uses to generate object code, including the interpretation of floating-point commands since the PDP-7 lacks dedicated hardware for these operations.
8. Operating Procedures and Error Handling: Offers a step-by-step guide for compiling, assembling, and executing FORTRAN II programs on a PDP-7 paper tape system. It also includes sections on compiler diagnostics and assembler error messages to aid in debugging.
9. Appendices: Contains character code equivalences (ASCII, 'A' and 'H' formats for FIODEC) and information on using extended memory to accommodate large arrays beyond the primary 8K core bank.