DECSYS-7 Operating Manual

DECSYS-7 is a DECtape-oriented operating system designed to facilitate FORTRAN programming on Digital Equipment's PDP-7 computer. It aims to reduce reliance on paper tape, minimize user intervention, optimize computer time, and enhance user-computer interaction. The system requires a PDP-7 configuration with at least 8,192 words of core memory, a DECtape Control Type 550, and two DECtape transports.

Each DECSYS-7 installation comes with a system master DECtape, which includes a Keyboard Monitor, eleven utility programs, FORTRAN input-output library routines, and eleven commonly used arithmetic functions. The system tape serves dual functions as a master/library and working tape, storing system programs, library routines, and user-developed FORTRAN programs. Users are recommended to create working copies of the master tape to safeguard the original contents.

The operating system offers three main categories of functions, managed through system programs called via the Keyboard Monitor:

1. System Tape Editing: Programs like UPDATE, LABEL, and CONTENTS enable users to copy entire system tapes, selectively copy or delete programs, add new programs from paper tape, and view/modify tape labels and program directories.
2. Working-Program Editing: The EDIT program allows users to modify, add, delete, list, print out, or create paper tapes for FORTRAN, intermediate language (assembler source), and relocatable binary versions of their programs.
3. FORTRAN Operations: COMPILE, ASSEMBLE, and LOAD are used for compiling FORTRAN source code, assembling intermediate language into relocatable binary, and loading programs for execution or debugging. These operations can be performed in either "wait" (user-intervened) or "go" (automatic) modes.

Operational control also involves specific DECtape transport assignments (logical units 1, 2, and 3 for system, user system/copy destination, and scratch tapes, respectively) and sense switches (AC0-AC3) that control data source selection, procedural statement printouts, paper tape character encoding (FIODEC/ASCII), and automatic tabulation. The system tape has a defined format, allocating specific blocks for labels, directories, and program storage. The manual details step-by-step procedures for system setup, operations, and error recovery.