SECONDARY STORAGE FACILITY FOR DATA PROCESSING SYSTEMS

This document is a 1976 United States Patent (No. 3,999,163) assigned to Digital Equipment Corporation. It describes a secondary storage facility (such as magnetic tape, disk, or drum units) designed to decouple the specific requirements of a drive from a particular data processing system.

The invention introduces a standardized interface using two distinct paths between a controller and a drive:

1. Asynchronous Drive Control Path: Carries control, status, and address information. This allows the controller and drive to operate independently of specific system architectures or word sizes.
2. Synchronous Data Path: Used for high-speed data transfers between the controller and the storage drive, managed via direct memory access or similar methods.

By standardizing these signal paths, the system allows for greater flexibility, enabling different types of drives to be interchanged or used with different computer systems without requiring new controller designs. The patent includes extensive technical documentation, including logic flow charts, register definitions, and timing diagrams for reading, writing, and diagnostic operations.