OpenVMS


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 services, hospitals and healthcare, 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 as VAX/VMS 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.. 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 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, 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.
File:Vms-albert-cheshire-cat.png|thumb|right|"Albert the Cheshire Cat" mascot for VAX/VMS, used by the DECUS VAX SIG
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 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 or MOS-32M 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

During the 1980s, DEC planned to replace the VAX platform and the VMS operating system with the PRISM architecture and the MICA operating system. When these projects were cancelled in 1988, a team was set up to design new VAX/VMS systems of comparable performance to RISC-based Unix systems. After a number of failed attempts to design a faster VAX-compatible processor, the group demonstrated the feasibility of porting VMS and its applications to a RISC architecture based on PRISM. This led to the creation of the Alpha architecture. The project to port VMS to Alpha began in 1989, and first booted on a prototype Alpha EV3-based Alpha Demonstration Unit in early 1991.
The main challenge in porting VMS to a new architecture was that VMS and the VAX were designed together, meaning that VMS was dependent on certain details of the VAX architecture. Furthermore, a significant amount of the VMS kernel, layered products, and customer-developed applications were implemented in VAX MACRO assembly code. Some of the changes needed to decouple VMS from the VAX architecture included the creation of the MACRO-32 compiler, which treated VAX MACRO as a high-level language, and compiled it to Alpha object code, and the emulation of certain low-level details of the VAX architecture in PALcode, such as interrupt handling and atomic queue instructions.
The VMS port to Alpha resulted in the creation of two separate codebases: one for VAX, and another for Alpha. The Alpha code library was based on a snapshot of the VAX/VMS code base circa V5.4-2. 1992 saw the release of the first version of OpenVMS for Alpha AXP systems, designated OpenVMS AXP V1.0. In 1994, with the release of OpenVMS V6.1, feature parity between the VAX and Alpha variants was achieved; this was the so-called Functional Equivalence release. The decision to use the 1.x version numbering stream for the pre-production quality releases of OpenVMS AXP confused some customers, and was not repeated in the subsequent ports of OpenVMS to new platforms.
When VMS was ported to Alpha, it was initially left as a 32-bit only operating system. This was done to ensure backwards compatibility with software written for the 32-bit VAX. 64-bit addressing was first added for Alpha in the V7.0 release. In order to allow 64-bit code to interoperate with older 32-bit code, OpenVMS does not create a distinction between 32-bit and 64-bit executables, but instead allows for both 32-bit and 64-bit pointers to be used within the same code. This is known as mixed pointer support. The 64-bit OpenVMS Alpha releases support a maximum virtual address space size of 8TiB, which is the maximum supported by the Alpha 21064 and Alpha 21164.
One of the more noteworthy Alpha-only features of OpenVMS was OpenVMS Galaxy, which allowed the partitioning of a single SMP server to run multiple instances of OpenVMS. Galaxy supported dynamic resource allocation to running partitions, and the ability to share memory between partitions.

Port to Intel Itanium

In 2001, prior to its acquisition by Hewlett-Packard, Compaq announced the port of OpenVMS to the Intel Itanium architecture. The Itanium port was the result of Compaq's decision to discontinue future development of the Alpha architecture in favour of adopting the then-new Itanium architecture. The porting began in late 2001, and the first boot on took place on January 31, 2003. The first boot consisted of booting a minimal system configuration on a HP i2000 workstation, logging in as the SYSTEM user, and running the DIRECTORY command. The Itanium port of OpenVMS supports specific models and configurations of HPE Integrity Servers. The Itanium releases were originally named HP OpenVMS Industry Standard 64 for Integrity Servers, although the names OpenVMS I64 or OpenVMS for Integrity Servers are more commonly used.
The Itanium port was accomplished using source code maintained in common within the OpenVMS Alpha source code library, with the addition of conditional code and additional modules where changes specific to Itanium were required. This required certain architectural dependencies of OpenVMS to be replaced, or emulated in software. Some of the changes included using the Extensible Firmware Interface to boot the operating system, reimplementing the functionality previously provided by Alpha PALcode inside the kernel, using new executable file formats, and adopting IEEE 754 as the default floating point format.
As with the VAX to Alpha port, a binary translator for Alpha to Itanium was made available, allowing user-mode OpenVMS Alpha software to be ported to Itanium in situations where it was not possible to recompile the source code. This translator is known as the Alpha Environment Software Translator, and it also supported translating VAX executables which had already been translated with VEST.
Two pre-production releases, OpenVMS I64 V8.0 and V8.1, were available on June 30, 2003, and on December 18, 2003. These releases were intended for HP organizations and third-party vendors involved with porting software packages to OpenVMS I64. The first production release, V8.2, was released in February 2005. V8.2 was also released for Alpha; subsequent V8.x releases of OpenVMS have maintained feature parity between the Alpha and Itanium architectures.