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87-418: PATHWORKS server ran on OpenVMS and Ultrix (and later Digital UNIX ) and enabled a system or cluster to act as a file and print server for client IBM PC compatible and Macintosh workstations. A version of PATHWORKS server for OS/2 was also available, allowing a PC with OS/2 to act as a server to other PCs. PATHWORKS server was derived from LanMan/X, the portable version of OS/2 LAN Manager . PATHWORKS

174-671: A Microsoft Windows , macOS or Linux workstation. DEC created a number of optional database products for VMS, some of which were marketed as the VAX Information Architecture family. These products included: In 1994, DEC sold Rdb, DBMS and CDD to Oracle , where they remain under active development. In 1995, DEC sold DSM to InterSystems , who renamed it Open M , and eventually replaced it with their Caché product. Examples of third-party database management systems for OpenVMS include MariaDB , Mimer SQL ( Itanium and x86-64 ), and System 1032 . VMS

261-449: A single system image abstraction. Nodes may be connected to each other via a proprietary hardware connection called Cluster Interconnect or via a standard Ethernet LAN . OpenVMS supports up to 96 nodes in a single cluster. It also allows mixed-architecture clusters. OpenVMS clusters allow applications to function during planned or unplanned outages. Planned outages include hardware and software upgrades. The DECnet protocol suite

348-569: A system administrator , but its services do not appear "up" to the end user or customer. The subject of the terms is thus important here: whether the focus of a discussion is the server hardware, server OS, functional service, software service/process, or similar, it is only if there is a single, consistent subject of the discussion that the words uptime and availability can be used synonymously. A simple mnemonic rule states that 5 nines allows approximately 5 minutes of downtime per year. Variants can be derived by multiplying or dividing by 10: 4 nines

435-637: A terminal server such as one of the DECserver family. DEC (and its successor companies) provided a wide variety of programming languages for VMS. Officially supported languages on VMS, either current or historical, include: Among OpenVMS's notable features is the Common Language Environment , a strictly defined standard that specifies calling conventions for functions and routines, including use of stacks , registers , etc., independent of programming language. Because of this, it

522-481: A VirtualBox VM with certain limitations; most significantly, few layered products were available, and code can only be compiled for x86-64 using cross compilers which run on Itanium-based OpenVMS systems. Following the V9.0 release, VSI released a series of updates on a monthly or bimonthly basis which added additional functionality and hypervisor support. These were designated V9.0-A through V9.0-H. In June 2021, VSI released

609-744: A common definition. DEC provided a collection of software development tools in a layered product named DECset (originally named VAXset ). This consisted of the following tools: The OpenVMS Debugger supports all DEC compilers and many third-party languages. It allows breakpoints, watchpoints and interactive runtime program debugging using either a command line or graphical user interface . A pair of lower-level debuggers, named DELTA and XDELTA , can be used to debug privileged code in additional to normal application code. In 2019, VSI released an officially supported Integrated Development Environment for VMS based on Visual Studio Code . This allows VMS applications to be developed and debugged remotely from

696-477: 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 (a 43-bit address space), which is the maximum supported by the Alpha 21064 and Alpha 21164 . One of the more noteworthy Alpha-only features of OpenVMS

783-404: A fault indicator activates. Failure is only significant if this occurs during a mission critical period. Modeling and simulation is used to evaluate the theoretical reliability for large systems. The outcome of this kind of model is used to evaluate different design options. A model of the entire system is created, and the model is stressed by removing components. Redundancy simulation involves

870-468: A half nines", but this is incorrect: a 5 is only a factor of 2, while a 9 is a factor of 10, so a 5 is 0.3 nines (per below formula: log 10 ⁡ 2 ≈ 0.3 {\displaystyle \log _{10}2\approx 0.3} ): 99.95% availability is 3.3 nines, not 3.5 nines. More simply, going from 99.9% availability to 99.95% availability is a factor of 2 (0.1% to 0.05% unavailability), but going from 99.95% to 99.99% availability

957-444: A hardware or software failure or environmental anomaly. Examples of unscheduled downtime events include power outages, failed CPU or RAM components (or possibly other failed hardware components), an over-temperature related shutdown, logically or physically severed network connections, security breaches, or various application , middleware , and operating system failures. If users can be warned away from scheduled downtimes, then

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1044-541: A higher level of privilege than most user code. This is in order to prevent accidental or malicious manipulation of the CLI's code and data structures by user-mode code. OpenVMS supports clustering (first called VAXcluster and later VMScluster ), where multiple computers run their own instance of the operating system. Clustered computers (nodes) may be fully independent from each other, or they may share devices like disk drives and printers. Communication across nodes provides

1131-466: A layered architecture, consisting of a privileged Executive , an intermediately privileged Command Language Interpreter, and unprivileged utilities and run-time libraries (RTLs). Unprivileged code typically invokes the functionality of the Executive through system services (equivalent to system calls in other operating systems). OpenVMS' layers and mechanisms are built around certain features of

1218-529: 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

1305-570: 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

1392-524: 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

1479-423: 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

1566-428: A true availability measure is holistic. Availability must be measured to be determined, ideally with comprehensive monitoring tools ("instrumentation") that are themselves highly available. If there is a lack of instrumentation, systems supporting high volume transaction processing throughout the day and night, such as credit card processing systems or telephone switches, are often inherently better monitored, at least by

1653-428: A voting scheme. This is used with complex computing systems that are linked. Internet routing is derived from early work by Birman and Joseph in this area. Active redundancy may introduce more complex failure modes into a system, such as continuous system reconfiguration due to faulty voting logic. Zero downtime system design means that modeling and simulation indicates mean time between failures significantly exceeds

1740-866: Is mean time to recovery (MTTR). Recovery time could be infinite with certain system designs and failures, i.e. full recovery is impossible. One such example is a fire or flood that destroys a data center and its systems when there is no secondary disaster recovery data center. Another related concept is data availability , that is the degree to which databases and other information storage systems faithfully record and report system transactions. Information management often focuses separately on data availability, or Recovery Point Objective , in order to determine acceptable (or actual) data loss with various failure events. Some users can tolerate application service interruptions but cannot tolerate data loss. A service level agreement ("SLA") formalizes an organization's availability objectives and requirements. High availability

1827-472: Is 50 minutes and 3 nines is 500 minutes. In the opposite direction, 6 nines is 0.5 minutes (30 sec) and 7 nines is 3 seconds. Another memory trick to calculate the allowed downtime duration for an " n {\displaystyle n} -nines" availability percentage is to use the formula 8.64 × 10 4 − n {\displaystyle 8.64\times 10^{4-n}} seconds per day. For example, 90% ("one nine") yields

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1914-441: 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

2001-402: Is a factor of 5 (0.05% to 0.01% unavailability), over twice as much. A formulation of the class of 9s c {\displaystyle c} based on a system's unavailability x {\displaystyle x} would be (cf. Floor and ceiling functions ). A similar measurement is sometimes used to describe the purity of substances. In general, the number of nines

2088-477: Is a result of maintenance that is disruptive to system operation and usually cannot be avoided with a currently installed system design. Scheduled downtime events might include patches to system software that require a reboot or system configuration changes that only take effect upon a reboot. In general, scheduled downtime is usually the result of some logical, management-initiated event. Unscheduled downtime events typically arise from some physical event, such as

2175-501: 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. In April 1975, Digital Equipment Corporation embarked on

2262-617: Is further subdivided between the Kernel , which consists of the code which runs at the kernel access mode, and the less-privileged code outside of the Kernel which runs at the executive access mode. The components of the Executive which run at executive access mode include the Record Management Services , and certain system services such as image activation. The main distinction between the kernel and executive access modes

2349-587: Is limited to 2 TiB volumes. DEC attempted to replace it with a log-structured file system named Spiralog, first released in 1995. However, Spiralog was discontinued due to a variety of problems, including issues with handling full volumes. Instead, there has been discussion of porting the open-source GFS2 file system to OpenVMS. An OpenVMS Command Language Interpreter (CLI) implements a command-line interface for OpenVMS, responsible for executing individual commands and command procedures (equivalent to shell scripts or batch files ). The standard CLI for OpenVMS

2436-406: Is not an actual goal, but rather a sarcastic reference to something totally failing to meet any reasonable target. Availability measurement is subject to some degree of interpretation. A system that has been up for 365 days in a non-leap year might have been eclipsed by a network failure that lasted for 9 hours during a peak usage period; the user community will see the system as unavailable, whereas

2523-409: Is not considered to be a failure unless the resulting performance decline exceeds the specification limits for the entire system. Active redundancy is used in complex systems to achieve high availability with no performance decline. Multiple items of the same kind are incorporated into a design that includes a method to detect failure and automatically reconfigure the system to bypass failed items using

2610-416: Is not often used by a network engineer when modeling and measuring availability because it is hard to apply in formula. More often, the unavailability expressed as a probability (like 0.00001), or a downtime per year is quoted. Availability specified as a number of nines is often seen in marketing documents. The use of the "nines" has been called into question, since it does not appropriately reflect that

2697-607: Is one of the primary requirements of the control systems in unmanned vehicles and autonomous maritime vessels . If the controlling system becomes unavailable, the Ground Combat Vehicle (GCV) or ASW Continuous Trail Unmanned Vessel (ACTUV) would be lost. On one hand, adding more components to an overall system design can undermine efforts to achieve high availability because complex systems inherently have more potential failure points and are more difficult to implement correctly. While some analysts would put forth

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2784-584: Is possible to call a routine written in one language (for example, Fortran) from another (for example, COBOL), without needing to know the implementation details of the target language. OpenVMS itself is implemented in a variety of different languages and the common language environment and calling standard supports freely mixing these languages. DEC created a tool named the Structure Definition Language (SDL), which allowed data type definitions to be generated for different languages from

2871-447: Is that most of the operating system's core data structures can be read from executive mode, but require kernel mode to be written to. Code running at executive mode can switch to kernel mode at will, meaning that the barrier between the kernel and executive modes is intended as a safeguard against accidental corruption as opposed to a security mechanism. The Kernel comprises the operating system's core data structures (e.g. page tables,

2958-529: Is the DIGITAL Command Language , although other options are available. Unlike Unix shells , which typically run in their own isolated process and behave like any other user-mode program, OpenVMS CLIs are an optional component of a process, which exist alongside any executable image which that process may run. Whereas a Unix shell will typically run executables by creating a separate process using fork-exec , an OpenVMS CLI will typically load

3045-549: Is tightly integrated into VMS, allowing remote logins, as well as transparent access to files, printers and other resources on VMS systems over a network. VAX/VMS V1.0 featured support for DECnet Phase II, and modern versions of VMS support both the traditional Phase IV DECnet protocol, as well as the OSI-compatible Phase V (also known as DECnet-Plus ). Support for TCP/IP is provided by the optional TCP/IP Services for OpenVMS layered product (originally known as

3132-474: Is used to achieve high availability by including enough excess capacity in the design to accommodate a performance decline. The simplest example is a boat with two separate engines driving two separate propellers. The boat continues toward its destination despite failure of a single engine or propeller. A more complex example is multiple redundant power generation facilities within a large system involving electric power transmission . Malfunction of single components

3219-440: The $ CMEXEC and $ CMKRNL system services, respectively. This allows code outside of system space to have direct access to the Executive's routines and system services. In addition to allowing third-party extensions to the operating system, Privileged Images are used by core operating system utilities to manipulate operating system data structures through undocumented interfaces. The typical user and application interface into

3306-592: The Apple Macintosh to serve as a terminal for VMS systems, or to use VMS systems as a file or print server. PATHWORKS was later renamed to Advanced Server for OpenVMS , and was eventually replaced with a VMS port of Samba at the time of the Itanium port. DEC provided the Local Area Transport (LAT) protocol which allowed remote terminals and printers to be attached to a VMS system through

3393-755: The VMS/ULTRIX Connection , then as the ULTRIX Communications Extensions or UCX). TCP/IP Services is based on a port of the BSD network stack to OpenVMS, along with support for common protocols such as SSH , DHCP , FTP and SMTP . DEC sold a software package named PATHWORKS (originally known as the Personal Computer Systems Architecture or PCSA) which allowed personal computers running MS-DOS , Microsoft Windows or OS/2 , or

3480-573: The file system is the Record Management Services (RMS), although applications can interface directly with the underlying file system through the QIO system services. The file systems supported by VMS are referred to as the Files-11 On-Disk Structures (ODS), the most significant of which are ODS-2 and ODS-5 . VMS is also capable of accessing files on ISO 9660 CD-ROMs and magnetic tape with ANSI tape labels . Files-11

3567-703: 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

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3654-510: The I/O database and scheduling data), and the routines which operate on these structures. The Kernel is typically described as having three major subsystems: I/O, Process and Time Management, Memory Management. In addition, other functionality such as logical name management, synchronization and system service dispatch are implemented inside the Kernel. OpenVMS allows user-mode code with suitable privileges to switch to executive or kernel mode using

3741-617: The N-x criteria. N represents the total number of components in the system. x is the number of components used to stress the system. N-1 means the model is stressed by evaluating performance with all possible combinations where one component is faulted. N-2 means the model is stressed by evaluating performance with all possible combinations where two component are faulted simultaneously. A survey among academic availability experts in 2010 ranked reasons for unavailability of enterprise IT systems. All reasons refer to not following best practice in each of

3828-724: The PATHWORKS client was a huge software stack to have resident in MS-DOS; configuring the PATHWORKS client was a complex task, made more so by the need to preserve enough conventional memory for DOS applications to run. To keep a reasonable amount of base memory free mandated the use of QEMM or a similar memory manager . This problem went away once 386-based PCs became prevalent and MS Windows provided built-in support for large amounts of memory. Lawrence W. White - PATHWORKS Product Manager Bob Nusbaum - PATHWORKS Product Manager OpenVMS OpenVMS , often referred to as just VMS ,

3915-698: 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 were 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

4002-588: The V9.1 Field Test, making it available to VSI's customers and partners. V9.1 shipped as an ISO image which can be installed onto a variety of hypervisors, and onto HPE ProLiant DL380 servers starting with the V9.1-A release. During the 1980s, the MICA operating system for the PRISM architecture was intended to be the eventual successor to VMS. MICA was designed to maintain backwards compatibility with VMS applications while also supporting Ultrix applications on top of

4089-402: The VAX architecture, including: These VAX architecture mechanisms are implemented on Alpha, Itanium and x86-64 by either mapping to corresponding hardware mechanisms on those architectures, or through emulation (via PALcode on Alpha, or in software on Itanium and x86-64). The OpenVMS Executive comprises the privileged code and data structures which reside in the system space. The Executive

4176-813: 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. 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,

4263-425: The ability of the user community to obtain a service or good, access the system, whether to submit new work, update or alter existing work, or collect the results of previous work. If a user cannot access the system, it is – from the user's point of view – unavailable . Generally, the term downtime is used to refer to periods when a system is unavailable. High availability is a property of network resilience ,

4350-510: The ability to "provide and maintain an acceptable level of service in the face of faults and challenges to normal operation." Threats and challenges for services can range from simple misconfiguration over large scale natural disasters to targeted attacks. As such, network resilience touches a very wide range of topics. In order to increase the resilience of a given communication network, the probable challenges and risks have to be identified and appropriate resilience metrics have to be defined for

4437-402: The allowed downtime is 8.64 × 10 − 1 {\displaystyle 8.64\times 10^{-1}} seconds per day. Percentages of a particular order of magnitude are sometimes referred to by the number of nines or "class of nines" in the digits. For example, electricity that is delivered without interruptions ( blackouts , brownouts or surges ) 99.999% of

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4524-492: The changes included using the Extensible Firmware Interface (EFI) to boot the operating system, reimplementing the functionality previously provided by Alpha PALcode inside the kernel, using new executable file formats ( Executable and Linkable Format and DWARF ), and adopting IEEE 754 as the default floating point format. As with the VAX to Alpha port, a binary translator for Alpha to Itanium

4611-595: 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

4698-882: The distinction is useful. But if the requirement is for true high availability, then downtime is downtime whether or not it is scheduled. Many computing sites exclude scheduled downtime from availability calculations, assuming that it has little or no impact upon the computing user community. By doing this, they can claim to have phenomenally high availability, which might give the illusion of continuous availability . Systems that exhibit truly continuous availability are comparatively rare and higher priced, and most have carefully implemented specialty designs that eliminate any single point of failure and allow online hardware, network, operating system, middleware , and application upgrades, patches, and replacements. For certain systems, scheduled downtime does not matter, for example, system downtime at an office building after everybody has gone home for

4785-407: The establishment of the company, as well as the development of VSI's own Itanium and Alpha releases of OpenVMS V8.4-x. The x86-64 port is targeted for specific servers from HPE and Dell , as well as certain virtual machine hypervisors . Initial support was targeted for KVM and VirtualBox . Support for VMware was announced in 2020, and Hyper-V is being explored as a future target. In 2021,

4872-430: The executable image into the same process, transfer control to the image, and ensure that control is transferred back to CLI once the image has exited and that the process is returned to its original state. Because the CLI is loaded into the same address space as user code, and the CLI is responsible for invoking image activation and image rundown, the CLI is mapped into the process address space at supervisor access mode,

4959-400: The exponent 4 − 1 = 3 {\displaystyle 4-1=3} , and therefore the allowed downtime is 8.64 × 10 3 {\displaystyle 8.64\times 10^{3}} seconds per day. Also, 99.999% ("five nines") gives the exponent 4 − 5 = − 1 {\displaystyle 4-5=-1} , and therefore

5046-531: The four privilege levels of OpenVMS in software since only two of x86-64's privilege levels are usable by OpenVMS. The first boot was announced on May 14, 2019. This involved booting OpenVMS on VirtualBox, and successfully running the DIRECTORY command. In May 2020, the V9.0 Early Adopter's Kit release was made available to a small number of customers. This consisted of the OpenVMS operating system running in

5133-430: The impact of unavailability varies with its time of occurrence. For large amounts of 9s, the "unavailability" index (measure of downtime rather than uptime) is easier to handle. For example, this is why an "unavailability" rather than availability metric is used in hard disk or data link bit error rates . Sometimes the humorous term "nine fives" (55.5555555%) is used to contrast with "five nines" (99.999%), though this

5220-851: 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 V3.0 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

5307-487: 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

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5394-536: The native Microsoft protocols. Later versions of PATHWORKS servers on VMS supported NetWare and Macintosh clients, but they never achieved the volumes of the Microsoft clients. For clients running a GUI such as Windows 3.x, additional components available included an X window system server, allowing clients to access graphical apps running on VMS or UNIX hosts, and clients for DEC's ALL-IN-1 email and groupware system. Although primitive by modern standards, PATHWORKS

5481-429: The night. Availability is usually expressed as a percentage of uptime in a given year. The following table shows the downtime that will be allowed for a particular percentage of availability, presuming that the system is required to operate continuously. Service level agreements often refer to monthly downtime or availability in order to calculate service credits to match monthly billing cycles. The following table shows

5568-466: The period of time between planned maintenance , upgrade events, or system lifetime. Zero downtime involves massive redundancy, which is needed for some types of aircraft and for most kinds of communications satellites . Global Positioning System is an example of a zero downtime system. Fault instrumentation can be used in systems with limited redundancy to achieve high availability. Maintenance actions occur during brief periods of downtime only after

5655-538: 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

5742-681: The primary command language interpreter (CLI) of OpenVMS since the first release. Other official CLIs available for VMS include the RSX-11 Monitor Console Routine (MCR) (VAX only), and various Unix shells . DEC provided tools for creating text-based user interface applications – the Form Management System (FMS) and Terminal Data Management System (TDMS), later succeeded by DECforms . A lower level interface named Screen Management Services (SMG$ ), comparable to Unix curses , also exists. Over

5829-566: The provisioning of services over the network, instead of the services of the network itself. This may require coordinated response from both the network and from the services running on top of the network. These services include: Resilience and survivability are interchangeably used according to the specific context of a given study. There are three principles of systems design in reliability engineering that can help achieve high availability. A distinction can be made between scheduled and unscheduled downtime. Typically, scheduled downtime

5916-423: The reason for this being that the most common cause for outages is human error. On the other hand, redundancy is used to create systems with high levels of availability (e.g. popular ecommerce websites). In this case it is required to have high levels of failure detectability and avoidance of common cause failures. If redundant parts are used in parallel and have independent failure (e.g. by not being within

6003-516: The same data center), they can exponentially increase the availability and make the overall system highly available. If you have N parallel components each having X availability, then you can use following formula: Availability of parallel components = 1 - (1 - X)^ N So for example if each of your components has only 50% availability, by using 10 of components in parallel, you can achieve 99.9023% availability. Two kinds of redundancy are passive redundancy and active redundancy. Passive redundancy

6090-613: The same kernel. MICA was ultimately cancelled along with the rest of the PRISM platform, leading Dave Cutler to leave DEC for Microsoft. At Microsoft, Cutler led the creation of the Windows NT operating system, which was heavily inspired by the architecture of MICA. As a result, VMS is considered an ancestor of Windows NT , together with RSX-11 , VAXELN and MICA, and many similarities exist between VMS and NT. A now-defunct project named FreeVMS attempted to develop an open-source operating system following VMS conventions. FreeVMS

6177-411: The service to be protected. The importance of network resilience is continuously increasing, as communication networks are becoming a fundamental component in the operation of critical infrastructures. Consequently, recent efforts focus on interpreting and improving network and computing resilience with applications to critical infrastructures. As an example, one can consider as a resilience objective

6264-522: The system administrator will claim 100% uptime. However, given the true definition of availability, the system will be approximately 99.9% available, or three nines (8751 hours of available time out of 8760 hours per non-leap year). Also, systems experiencing performance problems are often deemed partially or entirely unavailable by users, even when the systems are continuing to function. Similarly, unavailability of select application functions might go unnoticed by administrators yet be devastating to users –

6351-568: The theory that the most highly available systems adhere to a simple architecture (a single, high-quality, multi-purpose physical system with comprehensive internal hardware redundancy), this architecture suffers from the requirement that the entire system must be brought down for patching and operating system upgrades. More advanced system designs allow for systems to be patched and upgraded without compromising service availability (see load balancing and failover ). High availability requires less human intervention to restore operation in complex systems;

6438-400: The time would have 5 nines reliability, or class five. In particular, the term is used in connection with mainframes or enterprise computing, often as part of a service-level agreement . Similarly, percentages ending in a 5 have conventional names, traditionally the number of nines, then "five", so 99.95% is "three nines five", abbreviated 3N5. This is casually referred to as "three and

6525-418: The translation from a given availability percentage to the corresponding amount of time a system would be unavailable. The terms uptime and availability are often used interchangeably but do not always refer to the same thing. For example, a system can be "up" with its services not "available" in the case of a network outage . Or a system undergoing software maintenance can be "available" to be worked on by

6612-407: The users themselves, than systems which experience periodic lulls in demand. An alternative metric is mean time between failures (MTBF). Recovery time (or estimated time of repair (ETR), also known as recovery time objective (RTO) is closely related to availability, that is the total time required for a planned outage or the time required to fully recover from an unplanned outage. Another metric

6699-413: The x86-64 port was demonstrated running on an Intel Atom -based single-board computer . As with the Alpha and Itanium ports, the x86-64 port made some changes to simplify porting and supporting OpenVMS on the new platform including: replacing the proprietary GEM compiler backend used by the VMS compilers with LLVM , changing the boot process so that OpenVMS is booted from a memory disk, and simulating

6786-525: The years, VMS has gone through a number of different GUI toolkits and interfaces: High availability High availability ( HA ) is a characteristic of a system that aims to ensure an agreed level of operational performance, usually uptime , for a higher than normal period. There is now more dependence on these systems as a result of modernization. For instance, in order to carry out their regular daily tasks, hospitals and data centers need their systems to be highly available. Availability refers to

6873-526: 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. 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

6960-413: 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 (and version number) 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

7047-543: Was built on top of the L4 microkernel and supported the x86-64 architecture. Prior work investigating the implementation of VMS using a microkernel-based architecture had previously been undertaken as a prototyping exercise by DEC employees with assistance from Carnegie Mellon University using the Mach 3.0 microkernel ported to VAXstation 3100 hardware, adopting a multiserver architectural model. The OpenVMS operating system has

7134-708: 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 (AEST), 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,

7221-427: Was one of DEC's most successful products ever. Analysis of sales showed that on average, each PATHWORKS license brought in at least $ 3,000 USD in server revenue (server HW, SW, storage, printers, networking, and services), so it was a major driver for DEC's revenue in the mid and late 1980s. Later versions of PATHWORKS were known as Advanced Server for OpenVMS (or Advanced Sever for Unix for Tru64 ). Advanced Server

7308-630: Was originally designed to be used and managed interactively using DEC's text-based video terminals such as the VT100 , or hardcopy terminals such as the DECwriter series. Since the introduction of the VAXstation line in 1984, VMS has optionally supported graphical user interfaces for use with workstations or X terminals such as the VT1000 series. The DIGITAL Command Language (DCL) has served as

7395-480: 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. When VMS Software Inc. (VSI) announced that they had secured the rights to develop the OpenVMS operating system from HP, they also announced their intention to port OpenVMS to the x86-64 architecture. The porting effort ran concurrently with

7482-540: Was replaced on OpenVMS by Samba at the time of the porting of VMS to Itanium . This was due to the amount of effort required to keep Advanced Server compatible with new versions of Windows and the Server Message Block (SMB) protocol. Once installed onto the PCs, the PATHWORKS client provided the following features: The PATHWORKS server software provided access to server file storage and print services using

7569-471: Was very sophisticated for its time; far more than just a file and print server, it made client microcomputers into terminals and workstations on a DEC network. LanMan normally ran across Microsoft 's basic, non-routable NetBIOS/NetBEUI NBF protocol, but PATHWORKS included a DECnet stack, including layers like the LAT transport used for terminal sessions. The complexity of DECnet by 1980s PC standards meant that

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