3999163 Secondary Storage Facility For Data Processing Systems Jan74

This document describes a secondary storage facility for data processing systems designed to enhance flexibility and interoperability. The invention addresses the problem of previous systems where secondary storage drives and their controllers were custom-designed for specific data processing systems and lacked interchangeability.

The core of the invention is a standardized device bus interface that connects a controller to one or more secondary storage drives (such as magnetic tape, disk, or drum units). This device bus is characterized by two distinct communication paths:

1. Asynchronous Control Path: This path handles the transfer of control commands, address information, and status information between the controller and a selected drive. It allows the controller to initiate operations, configure drive registers, and receive status updates.
2. Synchronous Data Path: This path is dedicated to high-speed, block-oriented data transfers between the controller and the drive's storage medium. It includes data lines, parity lines, and synchronous clock signals to ensure precise data transmission.

A key benefit of this architecture is that it makes both the drives and the controllers largely independent of each other and of the specific data processing system they connect to. This modularity allows:

• Different types of drives (e.g., disk and tape) to be controlled by a single controller.
• New drive models to be introduced without requiring a complete redesign of the controller.
• The entire secondary storage facility to be integrated into various data processing system architectures with minimal modifications to the controller.

Data transfers between the controller and the main data processing system (e.g., central processing unit or main memory) typically occur via direct memory access (DMA) or equivalent methods, minimizing the central processor's involvement. This design significantly reduces engineering effort and improves the overall flexibility and interchangeability of data processing systems.