computer science

OpenVMS

OpenVMS is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand OpenVMS rather than just read about it. In short: OpenVMS, often referred to as just VMS, is a multi-user, multiprocessing and virtual memory-based operating system. It is designed to support time-sharing, batch processing, transaction processing and workstation applications.

OpenVMS — illustration

Key takeaways

OpenVMS belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect OpenVMS to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of OpenVMS from memory before moving on to harder problems.

Reference excerpt

OpenVMS, often referred to as just VMS, is a multi-user, multiprocessing and virtual memory-based operating system. It is designed to support time-sharing, batch processing, transaction processing and workstation applications. Customers using OpenVMS include banks and financial service providers, hospitals and healthcare providers, telecommunications operators, network information services, and industrial manufacturers. During the 1990s and 2000s, there were approximately half a million VMS systems in operation worldwide. It was first announced by Digital Equipment Corporation (DEC) as VAX/VMS (Virtual Address eXtension/Virtual Memory System) alongside the VAX-11/780 minicomputer in 1977. OpenVMS has subsequently been ported to run on DEC Alpha systems, the Itanium-based HPE Integrity Servers, and select x86-64 hardware and hypervisors. Since 2014, OpenVMS is developed and supported by VMS Software Inc. (VSI). OpenVMS offers high availability through clustering—the ability to distribute the system over multiple physical machines. This allows clustered applications and data to remain continuously available while operating system software and hardware maintenance and upgrades are performed, or if part of the cluster is destroyed. VMS cluster uptimes of 17 years have been reported.

History

Origin and name changes

In April 1975, Digital Equipment Corporation (DEC) embarked on a project to design a 32-bit extension to its PDP-11 computer line. The hardware component was code named Star; the operating system was code named Starlet. Roger Gourd was the project lead for VMS. Software engineers Dave Cutler, Dick Hustvedt, and Peter Lipman acted as technical project leaders. To avoid a repetition of PDP-11's many incompatible operating systems, the new operating system would be capable of real-time, time-sharing, and transaction processing. The Star and Starlet projects culminated in the VAX-11/780 computer and the VAX/VMS operating system. The Starlet project's code name survives in VMS in the name of several of the system libraries, including STARLET.OLB and STARLET.MLB. VMS was mostly written in VAX MACRO with some components written in BLISS. One of the original goals for VMS was backward compatibility with DEC's existing RSX-11M operating system. Prior to the V4.0 release, VAX/VMS included a compatibility layer named the RSX Application Migration Executive (RSX AME), which allowed user-mode RSX-11M software to be run unmodified on top of VMS. The RSX AME played an important role on early versions of VAX/VMS, which used certain RSX-11M user-mode utilities before native VAX versions had been developed. By the V3.0 release, all compatibility-mode utilities were replaced with native implementations. In VAX/VMS V4.0, RSX AME was removed from the base system, and replaced with an optional layered product named VAX-11 RSX.

By the early 1980s VAX/VMS was very successful in the market. Although created on Unix on DEC systems, Ingres ported to VMS believing that doing so was necessary for commercial success. Demand for the VMS version was so much greater that the company neglected the Unix version. A number of distributions of VAX/VMS were created:

MicroVMS was a distribution of VAX/VMS designed for MicroVAX and VAXstation hardware, which had less memory and disk space than larger VAX systems of the time. MicroVMS split up VAX/VMS into multiple kits, which a customer could use to install a subset of VAX/VMS tailored to their specific requirements. MicroVMS releases were produced for each of the V4.x releases of VAX/VMS and was discontinued when VAX/VMS V5.0 was released. Desktop-VMS was a short-lived distribution of VAX/VMS sold with VAXstation systems. It consisted of a single CD-ROM containing a bundle of VMS, DECwindows, DECnet, VAXcluster support, and a setup process designed for non-technical users. Desktop-VMS could either be run directly from the CD or could be installed onto a hard drive. Desktop-VMS had its own versioning scheme beginning with V1.0, which corresponded to the V5.x releases of VMS. An unofficial derivative of VAX/VMS named MOS VP (Russian: Многофункциональная операционная система с виртуальной памятью, МОС ВП, lit. 'Multifunctional Operating System with Virtual Memory') was created in the Soviet Union during the 1980s for the SM 1700 line of VAX clone hardware. MOS VP added support for the Cyrillic script and translated parts of the user interface into Russian. Similar derivatives of MicroVMS known as MicroMOS VP (Russian: МикроМОС ВП) or MOS-32M (Russian: МОС-32М) were also created. With the V5.0 release in April 1988, DEC began to refer to VAX/VMS as simply VMS in its documentation. In July 1992, DEC renamed VAX/VMS to OpenVMS as an indication of its support of open systems industry standards such as POSIX and Unix compatibility, and to drop the VAX connection since a migration to a different architecture was underway. The OpenVMS name was first used with the OpenVMS AXP V1.0 release in November 1992. DEC began using the OpenVMS VAX name with the V6.0 release in June 1993.

Port to Alpha

… excerpt ends here. Continue reading the full article.

Illustrations

OpenVMS: "Albert the Cheshire Cat" mascot for VAX/VMS, used by the DECUS VAX SIG[33][34] — "Albert the Cheshire Cat" mascot for VAX/VMS, used by the DECUS VAX SIG[33][34]

"Vernon the Shark" logo for OpenVMS[52]

"Swoosh" logo used by HP for OpenVMS

Worked examples

Example 1 — a first encounter with OpenVMS

Start with the simplest possible case. Write down what OpenVMS claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to OpenVMS before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about OpenVMS ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of OpenVMS

In research: OpenVMS appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses OpenVMS in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: OpenVMS is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1977 software, Cluster computing, Compaq software, so understanding it makes those chapters shorter.
In everyday life: Look for OpenVMS outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study OpenVMS in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what OpenVMS means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain OpenVMS out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is OpenVMS in simple terms?

Why does OpenVMS matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study OpenVMS?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on OpenVMS.