Functional Specification for TOPS-20 Common File System

This document outlines the functional specifications for the Common File System (CFS) designed for TOPS-20. CFS enables a multi-processor configuration (two or more 36-bit processors connected via a high-speed CI bus) to share disk structures and files as if they were a single system. Key aspects include:

• Product Overview: CFS provides a transparent, loosely-coupled architecture for sharing disk data without requiring physical connections to every disk from every processor.
• Architecture: It utilizes the CI (Computer Interconnect) bus and the SCA (Systems Communications Services) protocol. It is designed to be independent of other CI protocols like MSCP.
• Performance and Reliability: The system aims for minimal overhead (not exceeding 10% on file operations) and maintains high availability, where a processor failure does not affect the operation of others.
• Functional Details: The document describes file naming, open/close modes, data transfer primitives, and the use of the CFSSRV module for protocol control and interface management. It also notes current limitations, such as the initial support for two processors and specific constraints on certain file operations (e.g., no support for OF%DUD or concurrent ENQ/DEQ across processors).
• Protocol: CFS uses a 'veto' protocol, requiring approval from all involved processors for resource changes.