OpenVMS Compatibility Between VAX and AXP

This document, published in May 1993, provides a detailed comparison between OpenVMS on VAX and AXP (Alpha AXP) computers, aiming to assist current OpenVMS VAX users in assessing the impact of integrating OpenVMS AXP systems and migrating applications. It highlights the similarities and differences across end-user, system management, and programming environments, emphasizing Digital's commitment to compatibility while leveraging the performance benefits of the RISC-based Alpha AXP architecture.

Key aspects covered include:

• End-User Environment: Generally very similar to VMS Version 5.4-2, with DCL, editors, databases, and DECwindows Motif largely unchanged.
• System Management Environment: Most utilities and tasks are identical, but significant differences exist in memory page size (VAX 512 bytes vs. AXP 8K, 16K, 32K, or 64K bytes, using "pagelets" for compatibility), I/O subsystem configuration (SYSGEN vs. SYSMAN/AUTOGEN), MONITOR POOL command unavailability, and higher disk quotas for AXP. Some operating system functions and layered products were not yet supported on OpenVMS AXP Version 1.5.
• Programming Environment: Most DEC compilers and development tools (Linker, Librarian, Debuggers) are available. However, differences arise from the RISC architecture (e.g., atomic operations, memory access granularity, floating-point data handling), requiring potential code modifications. Cross-compilers are offered for migration from VAX to AXP.
• Interoperability: OpenVMS VAX and AXP systems can interoperate in networks (DECnet, TCP/IP) and VMSclusters. While network file transfers and remote logins are compatible, some network protocols, buses, and VMScluster capabilities (like tape serving by AXP nodes, volume shadowing) were not fully supported on OpenVMS AXP Version 1.5 at the time.
• Migration Resources: Digital provides various services, training, software (including DECmigrate for translating VAX binary images to AXP), and documentation to facilitate application migration. Investment protection programs are also offered to ease the transition.
• Application Portability: The document guides users on assessing application portability, particularly for VAX MACRO code, by identifying dependencies on VAX architecture, compiler differences, and diagnostic features. It also provides guidelines for developing new programs that are portable across both OpenVMS VAX and AXP systems.