TOPS-20 Multi-Access Disk Management Specification

This interoffice memorandum details the technical implementation for managing multi-accessed disks in TOPS-20. It defines the goals of ensuring data integrity, maintaining 5.1 compatibility, and minimizing disk writing overhead. Key sections cover configuration restrictions, dependencies on RSX20F, the user interface for declaring disk access levels ('don't-care'), and detailed descriptions of internal data structures such as the Processor Data Block (PDB) and Unit Data Block (UDB). The document also explains the disk access logic algorithm and the process for checking homeblocks during significant CI or disk events.