28 Oct67

This document, titled "PDP-X FORTRAN IV Initial Specifications" and authored by J. Cohen on October 14, 1967, serves as an initial definition of the FORTRAN IV language for the PDP-X computer. It is primarily intended for system programmers responsible for implementing the compiler, drawing heavily from the PDP-9 FORTRAN manual and aiming to include at least as much functionality as the PDP-9 language, while also referencing ASA specifications.

The specifications detail the language's fundamental components, including its 48-character set, data elements (Integer, Real, Double Precision, Logical, and Alphameric types), and variable/array definitions. It outlines rules for arithmetic and logical expressions, specifying operators, data modes, and precedence.

Key statements covered include arithmetic assignment, various control flow statements (Unconditional, Assigned, Computed GO TO; Arithmetic and Logical IF; DO loops; CONTINUE, PAUSE, STOP, and END statements).

Input/Output operations are extensively defined, describing formatted and unformatted READ and WRITE statements, I/O argument lists, and the comprehensive FORMAT statement with its diverse field descriptors (I, E, F, D, P, L, A, H, X, O for Octal). It also covers object-time formatting, printing formatted records, and auxiliary I/O (BACKSPACE, REWIND, ENDFILE, and the ENDFIL function).

Specification statements (TYPE, DIMENSION, COMMON, EQUIVALENCE, EXTERNAL, DATA) are detailed for memory allocation and variable properties. Finally, the document defines different categories of subprograms: Statement Functions, Intrinsic/Library Functions, External Functions, Subroutines, and Block Data Subprograms.

A significant appendix highlights key differences between PDP-X FORTRAN, PDP-9 FORTRAN, and ASA standards. Notable distinctions for PDP-X FORTRAN include:

• Permits quotation marks for alphameric data constants (not in ASA).
• Limits continuation cards to 5 (total 6 cards per statement), fewer than ASA's 19.
• Does not support complex data.
• Allows general integer expressions for subscripts and DO loop limits (more flexible than ASA).
• Excludes the G field descriptor from FORMAT statements.
• Does not support implied DO loops in DATA statements.
• Array sizes in subprograms are not adjustable.
• Includes an additional 'O' (Octal) format descriptor.