Functional Specification for TOPS-20 Common File System

This document describes the functional specification for the TOPS-20 Common File System (CFS), designed to enable shared access to disk structures across multiple 36-bit processors connected by a high-speed bus (CI). The system aims to provide transparent file access while maintaining compatibility with existing TOPS-20 standards. Key features include:

• Architecture: Supports configurations of up to four processors, requiring a shared CI connection. Each processor retains its own memory and direct access to public disk structures.
• Performance: Focuses on maintaining file operation overhead below 10%, utilizing the Mass Storage Control Protocol (MSCP) for efficient data transfer.
• Concurrency: Implements a 'write token' mechanism for managing simultaneous file modifications, ensuring data integrity across processors.
• Reliability: Designed for high availability with fail-soft capabilities, allowing system operation to continue if one processor fails.
• Implementation: Detailed plans are provided for the open file database, inter-processor locking, and the voting mechanism used to manage resource ownership.