Replacing VAXen with VAX Emulation

This document, presented at HP WORLD 2003, by Stanley F. Quayle, P.E. of Quayle Consulting Inc., discusses the process and considerations for replacing VAXen systems with VAX emulation.

The session goals include determining if VAX emulation is a viable option, how to select the best emulator and platform, and how to initiate the process. The document then delves into the challenges of porting, such as the availability of design documentation and source code, operating system and hardware dependencies, and the ability to reuse and validate code. It introduces emulation concepts like Wine, FreeVMS, and ACCELR8, illustrating how applications can run on different host operating systems and CPUs through emulation.

The presentation details how hardware emulation works by placing an emulator layer between the application and the host OS/CPU. It breaks down the emulator's task, including CPU emulation, memory management, and interaction with peripherals like Ethernet, disk controllers, tape controllers, and serial ports.

The document explores the cost-benefit analysis of emulation, highlighting the high cost of downtime and the savings achievable through maintenance reduction, while also noting potential performance improvements. It lists available emulators, categorizing them as open-source (SIMH, TS-10), freeware (PicoVAX), and commercial (CHARON-VAX), and compares the advantages of open-source and commercial solutions.

A significant portion is dedicated to evaluating the current system, identifying key items to check such as CPU usage, memory, network protocols, disk and tape drives, VMS version, layered product versions, and applications. It also points out risky areas like serial line dependencies, licensing considerations, operating system compatibility, and special hardware buses and interfaces.

The presentation offers guidance on choosing and sizing the host platform, recommending server-class machines with ample memory, processors, disk (SCSI), and network adapters. It includes performance data comparing various VAX models with CHARON-VAX configurations.

Finally, the document outlines strategies for disk migration, backup, and writing a comprehensive plan that includes testing, going live, and a backout strategy, concluding with considerations for post-migration support and new versions.