DECUS 82 PDP-1 FORTRAN Jul65

This document, DECUS No. 82, describes the FORTRAN FOR THE PDP-1 system, developed by the Air Force Technical Applications Center (AFTAC) and The Geotechnical Corporation in 1965. It is presented as a valuable tool for coding shorter programs on the PDP-1, rather than a full replacement for existing assembly languages.

The write-up details the FORTRAN language implementation, covering:

• Data Types & Variables: Integer (up to 131071) and floating-point constants (up to 10 digits, exponent ±38), with specific rules for variable naming (e.g., integer variables begin with i,j,k,l,m,n, max 6 characters). Notably, mixed-mode arithmetic is not allowed and not checked by the compiler.
• Statements: Includes standard arithmetic, supported functions (e.g., SIN, COS, SQRT, LOG), control flow (GO TO, IF, PAUSE, STOP, DO loops), DIMENSION, and END statements.
• Input/Output: Primarily supports typewriter and paper tape (FIO-DEC code) for TYPE, PUNCH FLEX, ACCEPT, and READ FLEX operations, along with detailed FORMAT specifications (i, f, x, h, a).

The FORTRAN system itself comprises seven paper tapes for compilation, loading, and execution. The document provides step-by-step instructions for this process, including the use of various sense switches for control. It also lists a comprehensive set of compiler-detected errors and runtime execution errors, aiding in debugging. Special features include runtime switches at specific memory addresses to control output behavior, escape characters for input, and the ability to insert DECAL (DEC's assembly language) code directly into FORTRAN programs.

Accompanying the write-up is a letter from DECUS, indicating that the programs were distributed from their Program Library and requesting users to review them for accuracy, ease of use, and clarity of documentation, with an offer of support for major issues.