VM is an early and influential virtual machine operating system from IBM, apparently the first true virtual machine system. (Some would argue it is still the only "true" virtual machine system.) It is in wide use on IBM mainframes today — and growing, largely because VM is all but mandatory to get maximum benefit from Linux on zSeries. In general terms, a virtual machine in computer science is software that creates an environment between the computer platform and the end user in which the end user can operate software. ... In computing, an operating system (aka, OS) is the system software responsible for the direct control and management of hardware and basic system operations. ... International Business Machines Corporation (IBM, or colloquially, Big Blue) (NYSE: IBM) (incorporated June 15, 1911, in operation since 1888) is headquartered in Armonk, New York, USA. The company manufactures and sells computer hardware, software, and services. ... Linux on zSeries (or Linux on System z9) is the preferred collective term for the Linux operating system and GNU/Linux software compiled to run on IBM mainframes, especially zSeries servers. ...

VM traces its roots to the System/360, specifically the Model 67, and an operating system called CP-67. Like the Apollo space program of the same era, this early VM version and its hardware platform were way ahead of their time. The Model 67 began to introduce the radical concept of a self-virtualizing processor instruction set, perfected in later models. Essentially VM and the mainframe hardware cooperate so that multiple instances of any operating system, each with protected access to the full instruction set, can peacefully and concurrently coexist. This virtualization capability is so strong that VM can run as a guest inside itself — even multiple levels deep! — without much performance penalty. The IBM System/360 (S/360) is a mainframe computer system family announced by International Business Machines on April 7, 1964. ... Apollo Program insignia Project Apollo was a series of human spaceflight missions undertaken by the United States of America using the Apollo spacecraft and Saturn launch vehicle, conducted during the years 1961–1972. ...

Businesses and governments find VM incredibly useful for software change management, testing, etc. Since VM allows mixing any arbitrary collection of operating system versions there's no need for "big bang" software migrations. If testing is not finished for one particular application, that's no problem — it can run on the older operating system alongside applications running on the new operating system. Nor is it necessary to purchase hundreds or even thousands of separate servers to offer these benefits. VM slices up a single mainframe, dynamically managing workload. For organizations with hundreds or even thousands of applications, this flexibility is essential.

VM has evolved over decades to increase performance, add functionality, keep up with processor hardware improvements, and improve reliability and security by enforcing ever-stricter isolation for guest operating systems. Versions along the way included VM/370, VM/390, and today's z/VM (which runs on zSeries, System z9, and certain earlier models). Also along the way VM picked up a feature called Conversational Monitor System, or CMS for short. The combination was (and sometimes still is) referred to as VM/CMS. Since December, 2001, IBM designates all its mainframes with the name eServer zSeries, with the e depicted in IBMs well-known red trademarked symbol. ... Since December, 2001, IBM designates all its mainframes with the name eServer zSeries, with the e depicted in IBMs well-known red trademarked symbol. ... The Conversational Monitor System (CMS) is a relatively simple interactive computing single-user operating system which was for many years IBMs principal time-sharing product. ...

With CMS, VM is a full fledged operating system in its own right (and not just a hypervisor). IBM and third parties offer many applications for VM/CMS, including DB2. Perhaps the most famous was OfficeVision, although today third parties offer HTTP servers, databases, etc. A hypervisor in computing is a scheme which allows multiple operating systems to run, unmodified, on a host computer at the same time. ... DB2® is IBMs family of information management software products. ... OfficeVision is an IBM proprietary office support application that runs on IBMs VM operating system and its user interface CMS. OfficeVision provides email, shared calendars, and shared document storage and management, and it provides an ability to link to other applications such as word/text editors. ... HTTP (for HyperText Transfer Protocol) is the primary method used to convey information on the World Wide Web. ...

Any mainframe operating system can run under VM. Nowadays the most popular is probably Linux on zSeries, and the major reason is that VM offers a level of sophisticated workload management on the mainframe that Linux alone does not yet offer. In particular, VM provides better memory (a.k.a. storage) management in a shared environment than Linux alone. VM also helps prevent a rogue Linux application from consuming "too much" CPU. It is common to run scores or even hundreds of Linux guests under z/VM — on a single mainframe server. Although Linux kernel crashes are rare, if a particular Linux guest crashes there is zero impact to any other part of the server. Other operating systems that run under VM include z/OS, z/VSE, z/TPF, MUSIC/SP, and z/VM itself — and all their predecessor versions. Linux on zSeries (or Linux on System z9) is the preferred collective term for the Linux operating system and GNU/Linux software compiled to run on IBM mainframes, especially zSeries servers. ... Intel 80486DX2 microprocessor in a ceramic PGA package A central processing unit (CPU), or sometimes simply processor, is the component in a digital computer that interprets and executes instructions and data contained in software. ... z/OS Welcome Screen seen through a terminal emulator The title of this article begins with a capital letter due to technical limitations. ... VSE (Virtual Storage Extended) is an operating system on the IBM System/370 and System/390 mainframe computers. ... TPF is also the NASA Terrestrial Planet Finder project. ... MUSIC/SP (Multi-User System for Interactive Computing / System Product) was developed at McGill University in the late 1960s from an IBM system called RAX (Remote Access). ...

Recently EMC and Microsoft have recognized the value of virtual machine technologies through their acquisitions of VMware and Virtual PC, respectively. However, VM has been refined over many decades, and it is unique as a robust, reliable, high performance, high-end server technology for running enterprise-scale mixed workloads. Fully self-virtualizing processor hardware technology is essential to VM's capabilities, and that same processor technology is not found in today's x86 and PowerPC CPUs. EMC is a TLA that may stand for: electric membership corporation electromagnetic compatibility Electro-Motive Corporation, the predecessor to General Motors Electro-Motive Division EMC Corporation European Marketing Confederation European Muon Collaboration Evergreen Marine Corporation This page concerning a three-letter acronym or abbreviation is a disambiguation page — a navigational... Microsoft Corporation (NASDAQ: MSFT, HKEx: 4338) is the worlds largest software company, with 2005 global annual sales of 40 billion US dollars and nearly 60,000 employees in more than 90 countries and regions. ... VMware Inc. ... Virtual PC is a virtualization suite for Apple Mac OS X and Microsoft Windows operating systems, originally created by Connectix, subsequently acquired by Microsoft. ... x86 or 80x86 is the generic name of a microprocessor architecture first developed and manufactured by Intel. ... PowerPC is a RISC microprocessor architecture created by the 1991 Apple-IBM-Motorola alliance, known as AIM. Originally intended for personal computers, PowerPC CPUs have since become popular embedded and high-performance processors as well. ...

See also

• RACF
• VM/CMS for the history of the development of the entire system, including CMS

RACF, short for Resource Access Control Facility, is an IBM software product. ... VM/CMS (Virtual Machine/Conversational Monitor System, originally called CP/CMS when it first appeared) is a bundled pair of operating systems used on IBM System/360, System/370, System/390, zSeries, and System z9 mainframes (and compatible systems). ...

Further reading

• Melinda Varian, VM and the VM Community: Past, Present, and Future (available here) is an excellent detailed history, starting with the experimental precursor to CP-67.

External links

• Short History of IBM's Virtual Machines
• The IBM 360/67 and CP/CMS