OpenVMS Compatibility Between VAX and Alpha

This document, published in May 1995, provides a comprehensive guide for OpenVMS VAX users looking to integrate OpenVMS Alpha systems into their computing environments or migrate existing applications. It thoroughly compares and contrasts OpenVMS Alpha Version 6.2 with OpenVMS VAX Version 6.2, focusing on features relevant to end-users, system managers, and programmers.

Key aspects covered include:

• Overview: Discusses the evolutionary path of OpenVMS Alpha, detailing similarities and differences in the Digital Command Language (DCL) environment, user interfaces (like DECwindows Motif), editors, help utilities, and password generators. For system managers, it highlights differences in disk quotas, I/O subsystem configuration, page size, security features, and VMScluster management, noting components that have achieved functional equivalence in Version 6.2. The programming environment section addresses the fundamental differences between VAX CISC and Alpha RISC architectures, compilers, linkers, debuggers, and outlines programming components not available on both platforms (e.g., specific floating-point data types, vector processing).
• Interoperability: Explains how OpenVMS VAX and Alpha systems can coexist and communicate in networks using DECnet and TCP/IP, as well as within mixed-architecture VMScluster systems. It covers supported network protocols, buses, and interconnects, along with restrictions and capabilities for booting, upgrades, and remote monitoring in mixed-version VMSclusters.
• Migration: Offers detailed information on transitioning to OpenVMS Alpha, including the availability of OpenVMS Alpha base operating system features, optional Digital software products, and third-party applications. It describes application migration paths, Digital's investment protection programs, migration services, training, and documentation resources like DECmigrate.
• Portability of Applications: Guides users on assessing application portability, identifying dependencies on the VAX architecture, and managing compiler differences. It outlines software support for portability, discusses programming environment differences on OpenVMS Alpha, and provides guidelines for developing applications that can run on both OpenVMS VAX and OpenVMS Alpha, especially in mixed-architecture VMScluster systems (covering user interface, system management, file format, data packing, data-type selection, buffer size, data access, and handling missing features).

The manual emphasizes Digital's commitment to ensuring compatibility and a clear migration path, allowing VAX users to leverage Alpha RISC technology with minimal disruption to their existing computing environments.