In computer science, a virtual machine (VM) is a software implementation of a machine (computer) that executes programs like a real machine. Computer science (or computing science) is the study and the Science of the theoretical foundations of Information and Computation and their

Contents 1 Definitions 1.1 System virtual machines 1.2 Process virtual machine 2 Techniques 2.1 Emulation of the underlying raw hardware (native execution) 2.2 Emulation of a non-native system 2.3 Operating system-level virtualization 3 List of hardware with virtual machine support 4 List of virtual machine software 4.1 Extended descriptions of selected virtualization software 5 Books 6 References 7 See also 8 External links

Definitions

A virtual machine was originally defined by Popek and Goldberg as an efficient, isolated duplicate of a real machine. The Popek and Goldberg virtualization requirements are a set of sufficient conditions for a computer architecture to efficiently support system Virtualization. Current use includes virtual machines which have no direct correspondence to any real hardware. ^[1]

Example: A program written in Java would receive services from the Java Runtime Environment software by issuing commands from which the expected result is returned by the Java software. A Java Virtual Machine ( JVM) is a set of computer software programs and data structures which use a Virtual machine By providing these services to the program, the Java software is acting as a "virtual machine," taking the place of the operating system or hardware for which the program would ordinarily have had to have been specifically written.

Virtual machines are separated in two major categories, based on their use and degree of correspondence to any real machine. A system virtual machine provides a complete system platform which supports the execution of a complete operating system (OS). In Computing, a platform describes some sort of Hardware architecture or Software framework (including Application frameworks, that allows An operating system (commonly abbreviated OS and O/S) is the software component of a Computer system that is responsible for the management and coordination In contrast, a process virtual machine is designed to run a single program, which means that it supports a single process. Computer programs (also software programs, or just programs) are instructions for a Computer. In computing a process is an instance of a Computer program that is being sequentially executed by a computer system that has the ability to run several computer An essential characteristic of a virtual machine is that the software running inside is limited to the resources and abstractions provided by the virtual machine -- it cannot break out of its virtual world.

System virtual machines

See also: Virtualization and Comparison of virtual machines

System virtual machines (sometimes called hardware virtual machines) allow the multiplexing of the underlying physical machine between different virtual machines, each running its own operating system. The table below compares basic information about Virtual machine (VM packages The software layer providing the virtualization is called a virtual machine monitor or hypervisor. In Computing, a hypervisor, also called virtual machine monitor, is a virtualization platform that allows multiple Operating systems to run on A hypervisor can run on bare hardware (Type 1 or native VM) or on top of an operating system (Type 2 or hosted VM).

The main advantages of system VMs are:

• multiple OS environments can co-exist on the same computer, in strong isolation from each other;
• the virtual machine can provide an instruction set architecture (ISA) that is somewhat different from that of the real machine. An instruction set is a list of all the instructions and all their variations that a processor can execute

Multiple VMs each running their own operating system (called guest operating system) are frequently used in server consolidation, where different services that used to run on individual machines in order to avoid interference are instead run in separate VMs on the same physical machine. This use is frequently called quality-of-service isolation (QoS isolation).

The desire to run multiple operating systems was the original motivation for virtual machines, as it allowed time-sharing a single computer between several single-tasking OSes.

The guest OSes do not have to be all the same, making it possible to run different OSes on the same computer (e. g. Microsoft Windows and Linux, or older versions of an OS in order to support software that has not yet been ported to the latest version). Microsoft Windows is a series of Software Operating systems and Graphical user interfaces produced by Microsoft. Linux (commonly pronounced ˈlɪnəks The use of virtual machines to support different guest OSes is becoming popular in embedded systems; a typical use is to support a real-time operating system at the same time as a high-level OS such as Linux or Windows. An embedded system is a special-purpose Computer system designed to perform one or a few dedicated functions often with Real-time computing constraints A real-time operating system ( RTOS; generally pronounced as "are-toss" is a multitasking Operating system intended for real-time

Another use is to sandbox an OS that is not trusted, possibly because it is a system under development. A sandbox is a testing (or virtual) environment that isolates untested code changes and outright experimentation from the production environment or Virtual machines have other advantages for OS development, including better debugging access and faster reboots. [1]

Alternative techniques such as Solaris Zones provides a level of isolation within a single operating system. Solaris Containers (including Solaris Zones) is an implementation of Operating system-level virtualization technology first made available in 2005 as part of This is not as complete isolation as a VM, as kernel exploits in a single zone affect all zones, whereas kernel exploits in a VM do not affect other VMs on the host. Zones are not virtual machines, but an example of "operating-system virtualization". This includes other "virtual environments" (also called "virtual servers") such as Virtuozzo, FreeBSD Jails, Linux-VServer, chroot jail and OpenVZ. Parallels Virtuozzo Containers is a proprietary Operating system-level virtualization product produced by Parallels Inc The FreeBSD jail mechanism is an implementation of Operating system-level virtualization that allows administrators to partition a FreeBSD -based Computer Linux-VServer is a Virtual private server implementation done by adding Operating system-level virtualization capabilities to the Linux kernel A chroot on Unix Operating systems is an operation that changes the apparent disk Root directory for the current running process and its children OpenVZ is an Operating system-level virtualization technology based on the Linux kernel and operating system These provide some form of encapsulation of processes within an operating system. These technologies have the advantage of being more resource-efficient than full virtualization; the disadvantage is that they can only run a single operating system and a single version/patchlevel of that operating system - so, for example, they cannot be used to run two applications, one of which only supports a newer OS version and the other only supporting an older OS version on the same hardware.

Process virtual machine

See also: Virtualization and Comparison of Application Virtual Machines

A process VM, sometimes called an application virtual machine, runs as a normal application inside an OS and supports a single process. This comparison lists some software Virtual machines that implement the concept of Application virtualization, typically for the purpose of allowing application binaries to be It is created when that process is started and destroyed when it exits. Its purpose is to provide a platform-independent programming environment that abstracts away details of the underlying hardware or operating system, and allows a program to execute in the same way on any platform. In Computing, a platform describes some sort of Hardware architecture or Software framework (including Application frameworks, that allows

A process VM provides a high-level abstraction (compared to the low-level ISA abstraction of the system VM) — that of a high-level programming language. In computing a high-level programming language is a Programming language with strong abstraction from the details of the computer Process VMs are implemented using an interpreter; performance comparable to compiled programming languages is achieved by the use of just-in-time compilation. In Computer science, an interpreter normally means a Computer program that executes, i In Computing, just-in-time compilation ( JIT) also known as dynamic translation, is a technique for improving the runtime performance of a Computer

This type of VM has become popular with the Java programming language, which is implemented using the Java virtual machine. A Java Virtual Machine ( JVM) is a set of computer software programs and data structures which use a Virtual machine Another example is the .NET Framework, which runs on a VM called the Common Language Runtime. The Common Language Runtime (CLR is the Virtual machine component of Microsoft's.

A special case of process VMs are systems that abstract over the communication mechanisms of a (potentially heterogeneous) computer cluster. Such a VM does not consist of a single process, but one process per physical machine in the cluster. They are designed to ease the task of programming parallel applications by letting the programmer focus on algorithms rather than the communication mechanisms provided by the interconnect and the OS. They do not hide the fact that communication takes place, and as such do not attempt to present the cluster as a single parallel machine.

Unlike other process VMs, these systems do not provide a specific programming language, but are embedded in an existing language; typically such a system provides bindings for several languages (e. g. C and FORTRAN). tags please moot on the talk page first! --> In Computing, C is a general-purpose cross-platform block structured Fortran (previously FORTRAN) is a general-purpose, procedural, imperative Programming language that is especially suited to Examples are PVM (Parallel Virtual Machine) and MPI (Message Passing Interface). Message Passing Interface ( MPI) is a specification for an API that allows many computers to communicate with one another They are not strictly virtual machines, as the applications running on top still have access to all OS services, and are therefore not confined to the system model provided by the "VM".

Techniques

Emulation of the underlying raw hardware (native execution)

This approach is described as full virtualization of the hardware, and can be implemented using a Type 1 or Type 2 hypervisor. The concept of full virtualization is well established in the literature but not always using this specific term In Computing, a hypervisor, also called virtual machine monitor, is a virtualization platform that allows multiple Operating systems to run on (A Type 1 hypervisor runs directly on the hardware; a Type 2 hypervisor runs on another operating system, such as Linux). Linux (commonly pronounced ˈlɪnəks Each virtual machine can run any operating system supported by the underlying hardware. Users can thus run two or more different "guest" operating systems simultaneously, in separate "private" virtual computers.

The pioneer system using this concept was IBM's CP-40, the first (1967) version of IBM's CP/CMS (1967-1972) and the precursor to IBM's VM family (1972-present). CP-40 was a research precursor to CP-67, which in turn was part of IBM's then-revolutionary CP[-67]/CMS &ndash a Virtual machine / Virtual memory CP/CMS was a Time-sharing Operating system of the late 60s and early 70s known for its excellent performance and advanced features CP/CMS|History of CP/CMS VM (often VM/CMS) refers to a family of IBM Virtual machine Operating systems used on IBM System/370 With the VM architecture, most users run a relatively simple interactive computing single-user operating system, CMS, as a "guest" on top of the VM control program (VM-CP). In Computer science, interactive computing refers to Software which accepts Input from humans — for example Data or Commands Interactive See also VM (operating system, CP/CMS, History of CP/CMS The Conversational Monitor System ( CMS; originally "Cambridge Monitor See also VM (operating system VM-CP was the official name of the control program portion of VM/370, a re-implementation of CP/CMS This approach kept the CMS design simple, as if it were running alone; the control program quietly provides multitasking and resource management services "behind the scenes". In addition to CMS, VM users can run any of the other IBM operating systems, such as MVS or z/OS. Multiple Virtual Storage, more commonly called MVS, was the most commonly used Operating system on the System/370 and System/390 IBM z/OS is a 64-bit Operating system for Mainframe computers, created by IBM. z/VM is the current version of VM, and is used to support hundreds or thousands of virtual machines on a given mainframe. See also VM (operating system z/VM is the current version in IBM's VM family of Virtual machine Operating systems. Some installations use Linux for zSeries to run Web servers, where Linux runs as the operating system within many virtual machines. Linux on System z is the collective term for the Linux operating system compiled to run on IBM mainframes especially System z machines The term web server can mean one of two things A Computer program that is responsible for accepting HTTP requests from web clients which are Linux (commonly pronounced ˈlɪnəks

Full virtualization is particularly helpful in operating system development, when experimental new code can be run at the same time as older, more stable, versions, each in a separate virtual machine. The process can even be recursive: IBM debugged new versions of its virtual machine operating system, VM, in a virtual machine running under an older version of VM, and even used this technique to simulate new hardware. Recursion, in Mathematics and Computer science, is a method of defining functions in which the function being defined is applied within its own definition International Business Machines Corporation abbreviated IBM and nicknamed "Big Blue", is a multinational Computer Technology CP/CMS|History of CP/CMS VM (often VM/CMS) refers to a family of IBM Virtual machine Operating systems used on IBM System/370 ^[2]

The standard x86 processor architecture as used in modern PCs does not actually meet the Popek and Goldberg virtualization requirements. See also X86 assembly language The generic term x86 refers to the most commercially successful Instruction set architecture in the history of Personal CPU design is the Design engineering task of creating a Central processing unit (CPU a component of Computer hardware. The Popek and Goldberg virtualization requirements are a set of sufficient conditions for a computer architecture to efficiently support system Virtualization. Notably, there is no execution mode where all sensitive machine instructions always trap, which would allow per-instruction virtualization.

Despite these limitations, several software packages have managed to provide virtualization on the x86 architecture, even though dynamic recompilation of privileged code, as first implemented by VMware, incurs some performance overhead as compared to a VM running on a natively virtualizable architecture such as the IBM System/370 or Motorola MC68020. x86 virtualization is the method by which X86 -based "guest" operating systems are run under another "host" x86 operating system with little or no modification In Computer science, dynamic recompilation (sometimes abbreviated to dynarec or the Pseudo-acronym DRC) is a feature of some Emulators VMware Inc ( is a Software developer and a global leader in the Virtualization market The Motorola 68020 is a 32-bit Microprocessor from Motorola, released in 1984. By now, several other software packages such as Virtual PC, VirtualBox, Parallels Workstation and Virtual Iron manage to implement virtualization on x86 hardware. Microsoft Virtual PC is a Virtualization suite for Microsoft Windows Operating systems and an Emulation suite for VirtualBox is an X86 virtualization software package originally created by German software company innotek now developed by Sun Microsystems as part Parallels Workstation is the first commercial software product released by Parallels Inc Virtual Iron Software, located in Lowell Massachusetts, provides software for Virtualization and management of a virtual infrastructure

On the other hand, plex86 can run only Linux under Linux using a specific patched kernel. Linux (commonly pronounced ˈlɪnəks It does not emulate a processor, but uses bochs for emulation of motherboard devices. Bochs is a portable X86 and AMD64 PC Emulator and Debugger mostly written in C++ and distributed as Free software

Intel and AMD have introduced features to their x86 processors to enable virtualization in hardware.

Emulation of a non-native system

Virtual machines can also perform the role of an emulator, allowing software applications and operating systems written for another computer processor architecture to be run. An emulator duplicates (provides an emulation of the functions of one System using a different system so that the second system behaves like (and appears to An operating system (commonly abbreviated OS and O/S) is the software component of a Computer system that is responsible for the management and coordination

Some virtual machines emulate hardware that only exists as a detailed specification. For example:

• One of the first was the p-code machine specification, which allowed programmers to write Pascal programs that would run on any computer running virtual machine software that correctly implemented the specification. In Computer programming, a p-code machine or pseudo-code machine is a specification of a CPU whose instructions are expected to be executed Pascal is an influential imperative and procedural Programming language, designed in 1968/9 and published in 1970 by Niklaus Wirth as a small Computer programs (also software programs, or just programs) are instructions for a Computer.
• The specification of the Java virtual machine. A Java Virtual Machine ( JVM) is a set of computer software programs and data structures which use a Virtual machine
• The Common Language Infrastructure virtual machine at the heart of the Microsoft .NET initiative. The Common Language Infrastructure (CLI is an open Specification (published under ECMA-335 and ISO/IEC 23271 developed by Microsoft that describes the executable
• Open Firmware allows plug-in hardware to include boot-time diagnostics, configuration code, and device drivers that will run on any kind of CPU. Open Firmware, or OpenBoot in Sun Microsystems parlance is a standard defining the interfaces of a computer Firmware system formerly endorsed by the

This technique allows diverse computers to run any software written to that specification; only the virtual machine software itself must be written separately for each type of computer on which it runs.

Operating system-level virtualization

Operating System-level Virtualization is a server virtualization technology which virtualizes servers on an operating system (kernel) layer. VMware Workstation is a Virtual machine software suite for X86 and X86-64 computers from VMware, a division of EMC Corporation. Ubuntu Kubuntu Edubuntu Xubuntu Gobuntu --> Ubuntu A server is a Computer dedicated to providing one or more services over a computer network typically through a request-response routine An operating system (commonly abbreviated OS and O/S) is the software component of a Computer system that is responsible for the management and coordination It can be thought of as partitioning: a single physical server is sliced into multiple small partitions (otherwise called virtual environments (VE), virtual private servers (VPS), guests, zones, etc); each such partition looks and feels like a real server, from the point of view of its users. A virtual private server ( VPS, also referred to as Virtual Dedicated Server or VDS) is a method of partitioning a physical server computer into multiple One example here is Solaris zones. You can have multiple guest OS running under the same OS (This is allowed on Solaris 10). But All guest OS have to use the same kernel level--you cannot run a different version; And also you cannot run a different OS than Solaris. Also AIX provides the same technique called Micro Partitioning

The operating system level architecture has low overhead that helps to maximize efficient use of server resources. The virtualization introduces only a negligible overhead and allows running hundreds of virtual private servers on a single physical server. A virtual private server ( VPS, also referred to as Virtual Dedicated Server or VDS) is a method of partitioning a physical server computer into multiple In contrast, approaches such as virtualisation (like VMware) and paravirtualization (like Xen or UML) cannot achieve such level of density, due to overhead of running multiple kernels. VMware Inc ( is a Software developer and a global leader in the Virtualization market In computing paravirtualization is a Virtualization technique that presents a software interface to Virtual machines that is similar but not identical to that of the Xen is a virtual machine monitor for IA-32, X86, X86-64, IA-64 and PowerPC 970 architectures User-mode Linux (UML allows multiple virtual Linux systems (known as guests to run as an application within a normal Linux system (known as the host From the other side, operating system-level virtualization does not allow running different operating systems (i. e. different kernels), although different libraries, distributions etc. are possible.

Main article: operating system-level virtualization

List of hardware with virtual machine support

• AMD-V (formerly code-named Pacifica)
• ARM TrustZone
• Boston Circuits gCore (grid-on-chip) with 16 ARC 750D cores and Time-machine hardware virtualization module. Operating system-level Virtualization is where the kernel of an Operating system allows for multiple isolated user-space instances (instead of just one x86 virtualization is the method by which X86 -based "guest" operating systems are run under another "host" x86 operating system with little or no modification x86 virtualization is the method by which X86 -based "guest" operating systems are run under another "host" x86 operating system with little or no modification The ARM architecture (previously the Advanced RISC Machine, and prior to that Acorn RISC Machine) is a 32-bit RISC processor architecture ARC International plc is a developer of configurable Microprocessor technology
• Freescale PowerPC MPC8572 and MPC8641D
• IBM System/370, System/390, and zSeries mainframes
• Intel VT (formerly code-named Vanderpool)
• Sun Microsystems Logical Domains (SPARC)

See also: X86 virtualization#Hardware support in x86 processors

List of virtual machine software

Process (Application) virtual machine software Common Language Runtime - C#, Visual Basic .NET, J#, Managed C++ EiffelStudio for the Eiffel programming language Erlang programming language Forth virtual machine - Forth Glulx - Glulx, Z-code Hec - Hasm Assembler Inferno - Limbo Java virtual machine - Java, Nice, NetREXX Low Level Virtual Machine (LLVM) - currently C, C++, Stacker Lua Macromedia Flash Player - SWF MMIX - MMIXAL Neko virtual machine - currently Neko and haXe O-code machine - BCPL p-code machine - Pascal Parrot - Perl 6 Perl virtual machine - Perl Portable.NET - C#, Visual Basic .NET, J#, Managed C++ YARV - Ruby MRI Rubinius - Ruby ScummVM - Scumm SECD machine - ISWIM, Lispkit Lisp Sed the stream-editor can also be seen as a VM with 2 storage spaces. Freescale Semiconductor Inc is an American Semiconductor manufacturer PowerPC is a RISC Instruction set architecture created by the 1991 Apple – IBM – Motorola alliance known as AIM International Business Machines Corporation abbreviated IBM and nicknamed "Big Blue", is a multinational Computer Technology The IBM System/370 (often S/370) was a model range of IBM mainframes announced on June 30, 1970 ESA/390 (Enterprise Systems Architecture/390 was introduced in September 1990 and is IBM 's last 31-bit -address/ 32-bit -data mainframe computing IBM System z, or earlier IBM eServer zSeries, is a brand name designated by IBM to all its Mainframe computers In 2000 IBM rebranded the existing x86 virtualization is the method by which X86 -based "guest" operating systems are run under another "host" x86 operating system with little or no modification x86 virtualization is the method by which X86 -based "guest" operating systems are run under another "host" x86 operating system with little or no modification Sun Microsystems Inc ( is a multinational vendor of Computers computer components Computer software, and Information technology services Logical Domains ( LDoms or LDOM) is a technology from Sun Microsystems which offers a virtualized computing environment abstracted from all physical SPARC (from Scalable Processor Architecture is a RISC Microprocessor Instruction set architecture originally x86 virtualization is the method by which X86 -based "guest" operating systems are run under another "host" x86 operating system with little or no modification The Common Language Runtime (CLR is the Virtual machine component of Microsoft's. C# (pronounced C Sharp is a Multi-paradigm Visual Basic.NET ( VBNET) is an object-oriented Computer language that can be viewed as an evolution of Microsoft's Visual Basic Managed Extensions for C++ or just Managed C++ is Microsoft 's set of deviations from C++ including grammatical and syntactic extensions keywords and attributes to bring the EiffelStudio is a development environment for the Eiffel programming language developed and distributed by Eiffel Software. Eiffel is an ISO -standardized Object-oriented Programming language designed to enable programmers to efficiently develop extensible reusable reliable Erlang is a general-purpose concurrent Programming language and Runtime system In Computer science, the term threaded code refers to a Compiler implementation technique where the generated code has a form that essentially consists entirely Forth is a structured, imperative, stack-based, computer Programming language and programming environment Glulx is a 32-bit portable Virtual machine intended for writing and playing Interactive fiction. Glulx is a 32-bit portable Virtual machine intended for writing and playing Interactive fiction. The Z-machine is a Virtual machine that was developed by Joel Berez and Marc Blank in 1979 and used by Infocom for its text adventure games Bytecode is a term which has been used to denote various forms of Instruction sets designed for efficient execution by a software interpreter as well as being suitable Inferno is an Operating system for creating and supporting distributed services Limbo is a Programming language for writing distributed systems and is the language used to write applications for the Inferno Operating system A Java Virtual Machine ( JVM) is a set of computer software programs and data structures which use a Virtual machine Nice is an advanced Object-oriented programming language. It features a powerful type system which can help eliminate many common bugs such as Null pointer dereferences REXX (REstructured eXtended eXecutor is an interpreted Programming language which was developed at IBM. The Low Level Virtual Machine, generally known as LLVM, is a Compiler infrastructure written in C++, which is designed for Compile-time tags please moot on the talk page first! --> In Computing, C is a general-purpose cross-platform block structured C++ (" C Plus Plus " ˌsiːˌplʌsˈplʌs is a general-purpose Programming language. In Computing, Lua (ˈluːa LOO-ah is a lightweight, reflective, imperative and procedural Programming language, The Adobe Flash Player is a widely distributed proprietary multimedia and application player created by Macromedia and now developed and distributed by Adobe The File format SWF (acronym of " Shockwave Flash "pronounced swiff)a partially open repository for multimedia and especially MMIX may also refer to the year 2009, in Roman numerals. MMIX (pronounced em-mix) is a 64-bit RISC MMIX may also refer to the year 2009, in Roman numerals. MMIX (pronounced em-mix) is a 64-bit RISC haXe is a Programming language, designed for creating interactive Web applications Currently there are four official compiler targets - Adobe Flash The O-code machine is a Virtual machine that was developed by Martin Richards in the late 1960s to give machine independence to BCPL, the low-level forerunner In Computer programming, a p-code machine or pseudo-code machine is a specification of a CPU whose instructions are expected to be executed Pascal is an influential imperative and procedural Programming language, designed in 1968/9 and published in 1970 by Niklaus Wirth as a small Parrot is a register -based Virtual machine being developed using the C programming language and intended to run Dynamic languages efficiently Perl 6 is a planned major revision to the Perl Programming language. NOTES FOR EDITORS "Perl" is not an acronym (read the "Name" section below NOTES FOR EDITORS "Perl" is not an acronym (read the "Name" section below Part of the DotGNU project PortableNET is a free and Open source software initiative aiming to build a portable Toolchain and C# (pronounced C Sharp is a Multi-paradigm Visual Basic.NET ( VBNET) is an object-oriented Computer language that can be viewed as an evolution of Microsoft's Visual Basic Managed Extensions for C++ or just Managed C++ is Microsoft 's set of deviations from C++ including grammatical and syntactic extensions keywords and attributes to bring the YARV is a Bytecode interpreter that was developed for the Ruby programming language by Koichi Sasada Matz's Ruby Interpreter or Ruby MRI is the reference implementation of the Ruby programming language. Rubinius is a Virtual machine and Compiler for Ruby created by Evan Phoenix. Ruby is a dynamic, reflective, general purpose Object-oriented programming language that combines syntax inspired by Perl with Smalltalk ScummVM is a collection of Game engine recreations Originally designed to play LucasArts adventure games that use the SCUMM system (the VM in SCUMM ( Script Creation Utility for Maniac Mansion) is a scripting language developed at LucasArts (known at the time as Lucasfilm Games to ease development The SECD machine is a highly influential Virtual machine intended as a target for functional programming language compilers ISWIM is an abstract computer Programming language (or a family of programming languages devised by Peter J Lispkit Lisp is a lexically scoped, Purely functional subset of Lisp (" Pure Lisp " developed as a testbed for Functional programming sed ( S tream ED itor refers to a Unix utility which (a parses text files and (b implements a Programming language which can apply textual transformations Smalltalk virtual machine - Smalltalk SQLite virtual machine - SQLite opcodes Squeak virtual machine - Squeak SWEET16 TrueType virtual machine - TrueType Valgrind - checking of memory accesses and leaks in x86/x86-64 code under Linux VX32 virtual machine - application-level virtualization for native code Virtual Processor (VP) from Tao Group (UK). Smalltalk is an object-oriented, dynamically typed, reflective programming language. Smalltalk is an object-oriented, dynamically typed, reflective programming language. SQLite is a mostly ACID -compliant Relational database management system contained in a relatively small (~500 kB) C programming library SQLite is a mostly ACID -compliant Relational database management system contained in a relatively small (~500 kB) C programming library The Squeak Programming language is a Smalltalk implementation derived directly from Smalltalk-80 by a group at Apple Computer that included some of the original Smalltalk-80 The Squeak Programming language is a Smalltalk implementation derived directly from Smalltalk-80 by a group at Apple Computer that included some of the original Smalltalk-80 SWEET16 is an interpreted " Byte-code " language invented by Steve Wozniak and implemented as part of the Integer BASIC ROM in the TrueType is an Outline font standard originally developed by Apple Computer in the late 1980s as a competitor to Adobe 's Type 1 fonts TrueType is an Outline font standard originally developed by Apple Computer in the late 1980s as a competitor to Adobe 's Type 1 fonts Valgrind is a Programming tool for memory debugging, Memory leak detection and profiling. See also X86 assembly language The generic term x86 refers to the most commercially successful Instruction set architecture in the history of Personal x86-64 is a Superset of the x86 instruction set architecture. Linux (commonly pronounced ˈlɪnəks The VX32 virtual extension environment is an application-level virtual machine implemented as an ordinary user-mode library and designed to run native X86 code Tao Virtual Processor (VP is a Virtual machine from Tao Group. Tao Group was a software company headquartered in Reading Berkshire, UK. The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom, the UK or Britain,is a Sovereign state located Waba - Virtual machine for small devices, similar to Java Warren Abstract Machine - Prolog, CSC GraphTalk Z-machine - Z-Code Zend Engine - PHP

System (Hardware) virtual machine software vThere (From Sentillion, Inc. In 1983 David H D Warren designed an Abstract machine for the execution of Prolog consisting of a memory architecture and an Instruction set Prolog is a Logic programming language It is a general purpose language often associated with Artificial intelligence and Computational linguistics CSC2jpg|thumb|250px|CSC's branch office in HITEC City, Hyderabad, India]] Computer Sciences Corporation (CSC is an Information technology The Z-machine is a Virtual machine that was developed by Joel Berez and Marc Blank in 1979 and used by Infocom for its text adventure games The Z-machine is a Virtual machine that was developed by Joel Berez and Marc Blank in 1979 and used by Infocom for its text adventure games The Zend Engine is an Open source Scripting engine (a Virtual Machine) commonly known for the important role it plays in the web automation language PHP is a computer Scripting language. Originally designed for producing Dynamic web pages it has evolved to include a Command line interface capability [2]) ATL (A MTL Virtual Machine) Bochs, portable open source x86 and AMD64 PCs emulator CoLinux Open Source Linux inside Windows Denali, uses paravirtualization of x86 for running para-virtualized PC operating systems. ATL is a model transformation language (MTL developed at INRIA to answer the QVT Request For Proposal Presentation Ubiquitous transformations The notion of Model transformation is of central importance to Information Technology. Bochs is a portable X86 and AMD64 PC Emulator and Debugger mostly written in C++ and distributed as Free software Cooperative Linux, abbreviated as coLinux, is software which allows Microsoft Windows and the Linux kernel to run simultaneously in parallel on the same In Computing, Denali is an Operating system, according to, "an IA-32 virtual machine monitor that allows for untrusted services to be run in isolated FAUmachine Hercules emulator, free System/370, ESA/390, z/Mainframe Integrity Workstation Green Hills Software[3] LilyVM is a lightweight virtual machineAn introduction Microsoft Virtual PC and Microsoft Virtual Server OKL4 from Open Kernel Labs Parallels Workstation, provides virtualization of x86 for running unmodified PC operating systems Parallels Desktop for Mac, provides virtualization of x86 for running virtual machines on Mac OS X or higher QEMU, is a simulator based on a virtual machine. FAUmachine is an Open source Virtual machine which emulates a PC The Hercules emulator is a computer program which allows software designed for IBM mainframe computers ( System/370, System/390 and ZSeries) to Microsoft Virtual PC is a Virtualization suite for Microsoft Windows Operating systems and an Emulation suite for Microsoft Virtual Server is a Virtualization solution that facilitates the creation of Virtual machines on the Windows XP, Windows Vista and Parallels Workstation is the first commercial software product released by Parallels Inc Parallels Desktop for Mac is a software product by Parallels Inc QEMU is a processor Emulator that relies on dynamic Binary translation to achieve a reasonable speed while being easy to port on new host CPU architectures SheepShaver. SheepShaver is an Open source PowerPC Apple Macintosh Emulator originally designed for BeOS and Linux. Simics SVISTA Trango Virtual Processors twoOStwo User-mode Linux VirtualBox Virtual Iron (Virtual Iron 3. Simics is a full-system simulator used to run unchanged production binaries of the target hardware at high-performance speeds SVISTA (Serenity Virtual Station is one of the commercial Software products promoted by Serenity Systems International. twoOStwo is one of the commercial software products developed by Parallels Software Studio User-mode Linux (UML allows multiple virtual Linux systems (known as guests to run as an application within a normal Linux system (known as the host VirtualBox is an X86 virtualization software package originally created by German software company innotek now developed by Sun Microsystems as part Virtual Iron Software, located in Lowell Massachusetts, provides software for Virtualization and management of a virtual infrastructure 1) Virtual Operating System from Star Virtual Machines VM from IBM VMware (ESX Server, Fusion, Virtual Server, Workstation, Player and ACE) Xen KVM IBM POWER SYSTEMS OS-level virtualization software OpenVZ Virtuozzo FreeVPS Linux-VServer FreeBSD Jails Solaris Containers AIX Workload Partitions

Extended descriptions of selected virtualization software

The following software products are able to virtualize the hardware so that several operating systems can share it. CP/CMS|History of CP/CMS VM (often VM/CMS) refers to a family of IBM Virtual machine Operating systems used on IBM System/370 International Business Machines Corporation abbreviated IBM and nicknamed "Big Blue", is a multinational Computer Technology VMware Inc ( is a Software developer and a global leader in the Virtualization market Xen is a virtual machine monitor for IA-32, X86, X86-64, IA-64 and PowerPC 970 architectures Kernel-based Virtual Machine (KVM is a Linux kernel Virtualization infrastructure OpenVZ is an Operating system-level virtualization technology based on the Linux kernel and operating system Parallels Virtuozzo Containers is a proprietary Operating system-level virtualization product produced by Parallels Inc FreeVPS is a GPL -licensed Virtualization patch for the Linux kernel developed by Positive Software Corporation. Linux-VServer is a Virtual private server implementation done by adding Operating system-level virtualization capabilities to the Linux kernel The FreeBSD jail mechanism is an implementation of Operating system-level virtualization that allows administrators to partition a FreeBSD -based Computer Solaris Containers (including Solaris Zones) is an implementation of Operating system-level virtualization technology first made available in 2005 as part of

• Adeos is a Hardware Abstraction Layer that can be loaded as a Kernel Module in Linux. Adeos ( Adaptive Domain Environment for Operating Systems) is a Nanokernel Hardware abstraction layer (HAL that operates between Computer hardware A hardware abstraction layer ( HAL) is an Abstraction layer, implemented in software between the physical hardware of a Computer and In Computing, a loadable kernel module (or LKM) is an Object file that contains code to extend the running kernel, or so-called base kernel Linux (commonly pronounced ˈlɪnəks It allows the loading of a real-time kernel as a module, at the same time as Linux but with higher priority.
• Denali uses paravirtualisation to provide high-performance virtual machines on x86 computers. In Computing, Denali is an Operating system, according to, "an IA-32 virtual machine monitor that allows for untrusted services to be run in isolated In computing paravirtualization is a Virtualization technique that presents a software interface to Virtual machines that is similar but not identical to that of the Denali's virtual machines support specialised minimal OSs for Internet services. The system can scale to thousands of virtual machines. Denali does not preserve the application binary interface (ABI), and so applications must be recompiled to run within a library operating system; in this sense it is similar to the Exokernel. Exokernel is an Operating system kernel developed by the MIT Parallel and Distributed Operating Systems group and also a class of similar operating systems
• OKL4 uses the open-source L4 microkernel as a hypervisor to provide a high-performance virtualization solution for embedded systems. L4 is a family of second-generation Microkernels based on theoriginal designs and implementations by German Computer scientist Jochen Liedtke.
• OpenVZ - Operating System-level server virtualization solution, built on Linux. OpenVZ is an Operating system-level virtualization technology based on the Linux kernel and operating system
• Parallels provides virtualization of x86 for running unmodified PC operating systems. Parallels Inc is a privately-held Virtualization technology company with offices all around the world (USA Germany, UK, France, Japan It also uses a lightweight hypervisor technology in order to improve security and to increase the efficiency. Parallels has become popular for its ability to run Windows as a guest under Mac OS X on the Apple-Intel architecture. Mac OS X (mæk oʊ ɛs tɛn is a line of computer Operating systems developed marketed and sold by Apple Inc, the latest of which is pre-loaded on all currently The Apple-Intel architecture is an unofficial name used for Apple Macintosh Personal computers developed and manufactured by Apple Computer that use
• QEMU is a simulator based on a virtual machine, which gives it the ability to emulate a variety of guest CPU architectures on many different host platforms. QEMU is a processor Emulator that relies on dynamic Binary translation to achieve a reasonable speed while being easy to port on new host CPU architectures
• Virtual Iron provides virtual machines for x86 that run unmodified operating systems, such as Windows, Red Hat and SUSE. Virtual Iron Software, located in Lowell Massachusetts, provides software for Virtualization and management of a virtual infrastructure Virtual Iron open source virtualization technology implements native virtualization, which delivers near-native performance for x86 operating systems.
• Virtuozzo replaces the hardware abstraction layer with a modified version enabling it to run with better performance of the OS, but forces all the VMs on a hardware box to all run the same OS, with some flexibility to support various Linux distributions on the same server. Parallels Virtuozzo Containers is a proprietary Operating system-level virtualization product produced by Parallels Inc Currently they have a version for Windows 2003 and for Linux. OpenVZ is a related open-source project providing similar functionality for Linux. OpenVZ is an Operating system-level virtualization technology based on the Linux kernel and operating system
• VMware provides virtual machines for x86 that can run unmodified PC operating systems. VMware Inc ( is a Software developer and a global leader in the Virtualization market The technology involved in doing this is complex and also incurs (sometimes significant) performance overheads with hosted VMware products (VM Server and Workstation). ESX server provides near-native performance and a fully virtualized option (along with para-virtualization of some hardware components). Xen trades running of existing operating systems for running modified (paravirtualized) operating systems with improved performance. Virtual Iron provides full OS compatibility for existing or new OSes with near-native performance without the performance trade-offs between paravirualization and binary translation.
• Xen Virtualization system whose motivation differs from that of Denali in that it is intended to run a moderate number of full-featured operating systems, rather than a large number of specialised, lightweight ones. Xen is a virtual machine monitor for IA-32, X86, X86-64, IA-64 and PowerPC 970 architectures
• KVM is a Linux kernel module that enables a modified QEMU program to use hardware virtualization. Kernel-based Virtual Machine (KVM is a Linux kernel Virtualization infrastructure Linux is an operating system kernel used by a family of Unix-like Operating systems These are popularly termed Linux operating systems and

Books

• Jim, Jr. Smith, Ravi Nair, James E. Smith, Heath Potter, Virtual Machines: Versatile Platforms For Systems And Processes, Publisher Morgan Kaufmann Publishers, May 2005, ISBN 1-55860-910-5, 656 pages
• Craig, Iain D. Virtual Machines. Springer, 2006, ISBN 1-85233-969-1

References

1. ^ Smith, Daniel E. ; Nair, Ravi (2005). "The Architecture of Virtual Machines". Computer 38 (5): 32–38. IEEE Computer Society. doi:10.1109/MC.2005.173. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
2. ^ See History of CP/CMS for IBM's use of virtual machines for operating system development and simulation of new hardware

See also

• Comparison of virtual machines
• Comparison of Application Virtual Machines
• Virtual appliance
• Computing
• ICL's VME operating system
• Gerrit Blaauw (A significant designer of the IBM/360, an early virtual computing architecture)
• LLVM (The University of Illinois's Low Level Virtual Machine, a compiler toolset)
• Threaded code (A common implementation technique for application virtual machines)
• Virtual keyboard
• Leostream (An easy to use P2V (Physical to Virtual) conversion utility)

External links

• The Reincarnation of Virtual Machines, Article on ACM Queue by Mendel Rosenblum, Co-Founder, VMware
• Performances comparison between Xen, UML, Vserver and VMware

See also CP/CMS, History of IBM This lengthy article explores the History of CP/CMS — the historical context in which this important IBM Time-sharing The table below compares basic information about Virtual machine (VM packages This comparison lists some software Virtual machines that implement the concept of Application virtualization, typically for the purpose of allowing application binaries to be A virtual appliance is a minimalist Virtual machine image designed to run under some sort of virtualization technology (like VMware Workstation, Citrix XenServer Computing is usually defined like the activity of using and developing Computer technology Computer hardware and software. International Computers Ltd, or ICL, was a large British Computer hardware, Computer software and Computer services company that operated from This article is about the operating system VME may also refer to the VMEbus computer bus Gerrit Anne (Gerry Blaauw (b July 17, 1924, The Hague Netherlands Ph The Low Level Virtual Machine, generally known as LLVM, is a Compiler infrastructure written in C++, which is designed for Compile-time This article is about the flagship campus For other uses and locations of University of Illinois, see University of Illinois (disambiguation The University of A compiler is a Computer program (or set of programs that translates text written in a computer language (the source language) into another In Computer science, the term threaded code refers to a Compiler implementation technique where the generated code has a form that essentially consists entirely A virtual keyboard is a software and/or hardware component that allows a user to enter characters Leostream is a Waltham Massachusetts -based company offering primarily two products for virtualization P>V Direct and the Virtual Desktop Connection Broker

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