DIGITAL STORAGE ARCHITECTURE PRODUCT SUMMARY

This document introduces Digital Equipment Corporation's (DIGITAL) Storage Architecture (DSA), a comprehensive framework designed to meet growing storage needs by offering flexible, expandable, and migratable storage products with standardized interfaces for major computer families (PDP-11, VAX-11, DECSYSTEM-20).

DSA structures mass storage functions into three distinct layers:

1. Host Layer: Simplified role, treating drives as generic devices and offloading complex storage tasks.
2. Controller Layer: Manages the bulk of mass storage functions, optimizing performance, validating data, performing error recovery, and presenting "clean" data to the host.
3. Drive/Media Layer: Handles physical data recording, playback, and mechanical controls like seeking.

The architecture emphasizes high I/O performance through features such as seek ordering, overlapped seeking across multiple drives/tapes, rotational optimization, data buffers, and direct revectoring. It ensures industry-leading data integrity with a powerful 170-bit Error Correction Code (ECC) for disks and a 16-bit Error Detection Code (EDC) for tapes, complemented by address verification, error logging, automatic sector retirement, and advanced disk mapping. System availability is enhanced by radial drive interconnects for fault isolation, comprehensive on-board diagnostics, automatic startup tests, and dual-access support for high-availability systems.

DSA aims to lower the total cost of ownership by offloading storage tasks from the host, ensuring hardware/software independence for seamless integration of new technologies, and supporting a broad range of current and future products. Current DSA products include UDA50 (UNIBUS) and HSC50 (CI) controllers, RA60 (removable), RA80, and RA81 (fixed) disk drives with various capacities, and the high-performance TA78 Tape Subsystem. The document highlights DSA's commitment to maximizing user-available capacity, robust data protection, optimized I/O, and high subsystem availability.