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 (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 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. 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 backwards compatibility with DEC's existing RSX-11M operating system. Prior to the V3.0 release, VAX/VMS included an 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 re-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. A number of distributions of VAX/VMS