OpenVMS

OpenVMS V7.3-1 running the CDE-based DECwindows GUI

The OpenVMS (Virtual Memory System) operating system (OS) is a multi-user, multiprocessing OS that was designed by Digital (now owned by Hewlett-Packard) for use in time sharing, batch processing, and transaction processing. It originally ran on VAX systems, and was later ported to the DEC Alpha and Intel Itanium.

Table of contents

1 History
2 Features

2.1 Clustering
2.2 Common Language Environment
2.3 Filesystem

3 OpenVMS Hobbyist
4 Glossary
5 External Links

History

OpenVMS was the direct successor to DEC's RSX-11 OS on the PDP-11. It was originally known as VAX-11/VMS when it was developed as the OS for Digital's 32-bit VAX line of minicomputers. It was renamed to VAX/VMS for version 2.0, at the same time as the VAX-11 computer was renamed to simply VAX. As of version V5.5 it was renamed again to OpenVMS to indicate its support for industry standards such as POSIX and Unix compatibility. The first version of OpenVMS for the 64-bit Digital Alpha system was released as OpenVMS AXP 1.0, but this name caused enough confusion amongst customers that V6.0 and later releases used the same version numbers for VAX and Alpha systems. As of version V8.0, OpenVMS was ported to HP systems using the Intel Itanium processor.

VAX/VMS was originally designed by Dave Cutler, who had earlier developed Digital's RSX-11 operating systems. Cutler was hired in 1988 by Microsoft to build the team that developed Windows NT.

Features

OpenVMS can be divided into three layers:

the kernel, made up of input/output, memory management, and process/time management subsystems.
core services, made up of DCL, RMS, DECwindows (OpenVMS's X11 compliant windowing system), and the RTLs.
utility programs for support, system management, and programming.

Clustering

OpenVMS supports clustering (called VAXcluster and later VMScluster), where multiple systems share processing, job queues, print queues, and disk storage, connected either by specialized hardware or Ethernet. An Ethernet-based cluster is called a LAVC, for local area network VMScluster. OpenVMS supports up to 96 nodes in a single cluster, and allows mixed-architecture clusters, where VAX and Alpha systems, or Alpha and Itanium systems can co-exist in a single cluster (OpenVMS Engineering has suggested that triple-architecture clusters are possible in theory, but are not supported by HP).

Common Language Environment

Among OpenVMS's notable features is the Common Language Environment, a strictly defined standard that specifies calling convention for functions and routines, including use of stack, registerss, etc., independently of programming language. Because of this, it is possible to call a routine written in one language—such as FORTRAN—from another, such as C, without needing to know the implementation details of the target language. OpenVMS itself is implemented in a large variety of different languages (such as BLISS, VAX Macro, Ada, PL/I, C, Fortran, and several others), in contrast to a system such as Unix which is implemented nearly entirely in the C language.

Filesystem

OpenVMS has a very rich filesystem, with support for stream and record-oriented IO, ACLs, file versioning, etc. See OpenVMS filesystem.

OpenVMS Hobbyist

Despite being a commercial operating system, OpenVMS and several layered products were made available free of charge in 1997, for hobbyist, non-commercial use as part of the OpenVMS Hobbyist Program. Since then, several companies producing OpenVMS software have made their products available under the same terms, such as Process Software.

Glossary

DCL - Digital Command Language - command line interface.
DECwindows - Digital's implementation of the X Window System.
RMS - Record Management Services - high-level, language/device-independent IO.
RTL - Runtime Libraries - shared routines and functions, callable from any language.
FDL - File Description Language - defines file record/field structure.
DECnet - Digital's proprietary networking architecture.