Virtual Machine
Content
Virtual Machine The Need for a Virtual Machine
Faced with large, heterogeneous information systems and the accelerated rate of technological innovation, software engineers are beginning to rediscover the benefits of targeting virtual machines. The name of the game in software development is return on investment. Companies want to invest money in software that will be useful long enough for the resources spent to be justified. Porting a software package from one platform to another is costly and, depending on the number of platforms supported, can prove to be a Sisyphean nightmare. The worst-case scenario occurs when business logic is stranded on an aging system. Due to historical forces, a large base of code may end up on an obsolete platform that no one wants to deal with. The people who wrote the original code have either quit or been promoted and don't remember anything (sometimes intentionally). The source code has been transformed by time into an encrypted historical artifact that will require years of work by researchers to decipher. If the language and tools used to develop the initial code are linked to the original platform, porting may be out of the question. In pathological cases, the code may be so obscure and illegible that maintenance engineers are too scared to touch anything. I'm sure Y2K programmers are familiar with this type of imbroglio. The only recourse may be a complete rewrite and this is an extremely expensive alternative, fraught with all sorts of dangers and hidden costs. This is the kind of situation CIOs lose sleep over. Using a virtual machine offers a degree of insurance against this kind of thing happening. When confronted with a new hardware platform or operating system, the only application that needs to be ported is the virtual machine itself. If a virtual machine is, say, 100,000 lines of code, you might think that actually porting the code is a bad investment. 100,000 lines of code is not a trivial porting job. However, let's say that the virtual machine runs an application suite that consists of 11 million lines of code. Suddenly, porting the virtual machine is not such a bad deal because the alternative would be to port the 11 million lines of application code. Don't think that this isn't realistic. I once visited an automobile insurance company that had around 30 million lines of application code.
Dept. of Computer Engineering, ICOER, Pune.
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Virtual Machine
OBJECTIVE:
Objective was to build a virtual machine that satisfied three criterion. In order of priority, these are: 1. Portability 2. Simplicity 3. Performance Portability is the most important feature because being able to work with a uniform software interface, across multiple platforms, is the primary benefit of using a virtual machine. If you can't port a virtual machine, then you're stuck with a given platform, in which case you might as well use tools that compile to the native machine encoding. Portability is also the most important priority in the sense that I had to make sacrifices in terms of simplicity and performance in order to achieve it. There is rarely a solution that is ever optimal under all conditions in software engineering. One way of boosting performance would be to make heavy use of assembly code. However, using an assembler does not necessarily guarantee faster program execution. In order to be able to justify using an assembler, the programmer has to have an intimate knowledge of both the assembly code a compiler generates and the kind of optimizations it performs. The goal is to be able to write faster assembly code than the compiler can. This requires a certain amount of vigilance and skill because, in most cases, the optimizer in a C compiler can do a better job than the average programmer. Another problem with using assembly language is that it ties your code to the hardware you're working on. To port the code to new hardware, you'll need to rewrite every single line of assembly code. This can turn out to be much more work than you think. Again, in the effort to maintain a certain degree of portability, I opted out of low-level, high-performance assembly coding and wrote everything in ANSI C. simplicity has priority over performance by virtue of my desire to make the code maintainable. A year from now, I would like to be able to modify my code without having to call in a team of archaeologists. Code that is optimized for performance can become very brittle and resistant to change. Developers writing high-performance C code will often use all sorts of misleading and confusing conventions, like bitwise shifting to divide by 2. What is produced is usually illegible by anyone but the original developer, and given enough time even the original developer may forget what he had done and why he had done it. In an extreme case, a programmer who has created a mess and is too scared to clean it up may opt to quit and go work somewhere else. I've heard people refer to this as "the final solution" or "calling in for air support and pulling out."
Dept. of Computer Engineering, ICOER, Pune.
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Virtual Machine
Run-time Systems
A run-time system is an environment in which computer programs execute. A run-time system provides everything a program needs in order to run. For example, a run-time system is responsible for allocating memory for an application, loading the application into the allocated memory, and facilitating the execution of the program's instructions. If the program requests services from the underlying operating system through the invocation of system calls, the runtime system is in charge of handling those service requests. For instance, if an application wants to perform file I/O, the run-time system must offer a mechanism to communicate with the disk controller and provide read/write access. There are different kinds of run-time systems. One way to classify run-time systems is to categorize them based on how they execute a program's instructions. For programs whose instructions use the processor's native machine encoding, the run-time system consists of a tightly knit collaboration between the computer's processor and the operating system. The processor provides a mechanism for executing program instructions. The CPU does nothing more than fetch instructions from memory, which are encoded as numeric values, and perform the actions corresponding to those instructions. The operating system implements the policy side of a computer's native run-time system. The CPU may execute instructions, but the operating system decides how, when, and where things happen. Think of the operating system as a fixed set of rules the CPU has to obey during the course of instruction execution. Thus, for programs written in native machine instructions, the computer itself is the runtime system. Program instructions are executed at the machine level, by the physical CPU, and the operating system manages how the execution occurs. This type of run-time system involves a mixture of hardware and software. Programs whose instructions are not directly executed by the physical processor require a run-time system that consists entirely of software. In such a case, the program's instructions are executed by a virtual machine. A virtual machine is a software program that acts like a computer. It fetches and executes instructions just like a normal processor. The difference is that the processing of those instructions happens at the software level instead of the hardware level. A virtual machine also usually contains facilities to manage the path of execution and to offer an interface to services normally provided by the native operating system. A virtual machine is defined by a specification. A virtual machine is not a particular software implementation, but rather a set of rules. These rules form a contract that the engineer, who builds an instantiation of the virtual machine, must honor. A virtual machine can be implemented in any programming language on any hardware platform, as long as it obeys the specification. You could create a version of the HEC virtual machine on an OS/390 using APL if you really wanted to. This is what makes the idea of a virtual machine so powerful. You can run HEC executables, without recompilation, anywhere there is a run-time system that obeys the specification.
Dept. of Computer Engineering, ICOER, Pune.
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Virtual Machine Definitions
Virtual machine was originally defined by Popek and Goldberg as "an efficient, isolated duplicate of a real machine". Current use includes virtual machines which have no direct correspondence to any real hardware. Virtual machines are separated into 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 contrast, a process virtual machine is designed to run a single program, which means that it supports a single process. 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. Example: A program written in Java receives services from the Java Runtime Environment (JRE) software by issuing commands to, and receiving the expected results from, the Java software. 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 be tailored.
Dept. of Computer Engineering, ICOER, Pune.
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Virtual Machine System virtual machines
System virtual machines (sometimes called hardware virtual machines) allow the sharing of the underlying physical machine resources between different virtual machines, each running its own operating system. The software layer providing the virtualization is called a virtual machine monitor or hypervisor. 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
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). 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. Another use is to sandbox an OS that is not trusted, possibly because it is a system under development. Virtual machines have other advantages for OS development, including better debugging access and faster reboots.[2] Alternate techniques such as Solaris Zones provides a level of isolation within a single operating system. This does not have isolation as complete as a VM. A kernel exploit in a system with multiple zones will affect all zones. Achieving the same goal in a virtual machine implementation would require exploiting a weakness in the hypervisor. A hypervisor typically has a smaller "attack surface" than a complete operating system, making this more challenging. Further, a kernel exploit in a VM guest would not affect other VMs on the host, just as a successful intrusion into one zone would not necessarily affect other zones. 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, LinuxVServer, chroot jail, and OpenVZ. These provide some form of encapsulation of processes within an operating system. These technologies have the advantages of being more resourceefficient than full virtualization and having better observability into multiple guests
Dept. of Computer Engineering, ICOER, Pune.
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Virtual Machine
simultaneously; the disadvantage is that, generally, they can only run a single operating system and a single version/patch level 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. However, Sun Microsystems has enhanced Solaris Zones to allow some zones to behave like Solaris 8 or Solaris 9 systems by adding a system call translator
Process virtual machines
A process VM, sometimes called an application virtual machine, runs as a normal application inside an OS and supports a single process. It is created when that process is started
Dept. of Computer Engineering, ICOER, Pune.
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Virtual Machine
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. A process VM provides a high-level abstraction — that of a high-level programming language (compared to the low-level ISA abstraction of the system VM). Process VMs are implemented using an interpreter; performance comparable to compiled programming languages is achieved by the use of just-in-time compilation. This type of VM has become popular with the Java programming language, which is implemented using the Java virtual machine. Another example is the .NET Framework, which runs on a VM called the Common Language Runtime. 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). Examples are PVM (Parallel Virtual Machine) and MPI (Message Passing Interface). 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".
List of hardware with virtual machine support Dept. of Computer Engineering, ICOER, Pune.
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Virtual Machine
Alcatel-Lucent 3B20D/3B21D emulated on commercial off-the-shelf computers with 3B2OE or 3B21E system • 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. • Freescale PowerPC MPC8572 and MPC8641D • IBM System/370, System/390, and zSeries mainframes • Intel VT (formerly code-named Vanderpool) • Sun Microsystems sun4v (UltraSPARC T1 and T2) -- utilized by Logical Domains
• • • • •
HP vPAR and cell based nPAR GE Project MAC then Honeywell Multics systems Honeywell 200/2000 systems Liberator replacing IBM 14xx systems, Level 62/64/66 IBM System/360 Model 145 Hardware emulator for Honeywell 200/2000 systems RCA Spectra/70 Series emulated IBM System/360 NAS CPUs emulated IBM and Amdahl machines Honeywell Level 6 minicomputers emulated predecessor 316/516/716 minis Xerox Sigma 6 CPUs were modified to emulate GE/Honeywell 600/6000 systems
GCOS
• • • • •
List of virtual machine software
Process (Application) virtual machine System (Hardware) virtual machine 8
Dept. of Computer Engineering, ICOER, Pune.
Virtual Machine
software
•
software[clarification needed]
Common Language Infrastructure - C#, • ATL (A MTL Virtual Machine) Visual Basic .NET, J#, C++/CLI (formerly • Bochs, portable open source x86 and Managed C++) AMD64 PCs emulator • Dalvik virtual machine - part of the • CoLinux Open Source Linux inside Android mobile phone platform Windows • Dis - Inferno operating system and its • Denali, uses paravirtualization of x86 Limbo programming language for running para-virtualized PC operating • Dosbox systems. • EiffelStudio for the Eiffel programming • FAUmachine language • Hercules emulator, free System/370, • Erlang programming language ESA/390, z/Mainframe • Forth virtual machine - Forth • KVM • Glulx - Glulx, Z-code • LilyVM is a lightweight virtual • Hec - Hasm Assembler machineAn introduction • Java Virtual Machine - Java, Nice, • Logical Domains NetREXX • Microsoft Virtual PC and Microsoft • Low Level Virtual Machine (LLVM) - Virtual Server currently C, C++, Stacker • OKL4 from Open Kernel Labs • Lua • Oracle VM • Macromedia Flash Player - SWF • OVPsim [1] is a freely available virtual • MMIX - MMIXAL platform simulator designed to simulate • Neko virtual machine - currently Neko complex multiprocessor systems at very high and haXe speeds • O-code machine - BCPL • Parallels Workstation, provides • p-code machine - Pascal virtualization of x86 for running unmodified • Parrot - Perl 6 PC operating systems • Perl virtual machine - Perl • Parallels Desktop for Mac, provides • CPython - Python virtualization of x86 for running virtual • YARV - Ruby MRI machines on Mac OS X or higher • Rubinius - Ruby • QEMU, is a simulator based on a • ScummVM - Scumm virtual machine. • SECD machine - ISWIM, Lispkit Lisp • SheepShaver. • Sed the stream-editor can also be seen • Simics as a VM with 2 storage spaces. • Sun xVM • Smalltalk virtual machine - Smalltalk • SVISTA • SQLite virtual machine - SQLite • Trango Virtual Processors opcodes • twoOStwo • Squeak virtual machine - Squeak • User-mode Linux • SWEET16 • VirtualBox • Tamarin (JavaScript engine) • Virtual Iron (Virtual Iron 3.1) ActionScript VM in Flash 9 • VM from IBM • TrueType virtual machine - TrueType • VMware (ESX Server, Fusion, Virtual • Valgrind - checking of memory Server, Workstation, Player and ACE) accesses and leaks in x86/x86-64 code under • vSMP Foundation (From ScaleMP)
Dept. of Computer Engineering, ICOER, Pune.
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Virtual Machine
Linux
•
Virtual Processor (VP) from Tao Group
• •
Xen IBM POWER SYSTEMS
(UK).
• VX32 virtual machine - applicationlevel virtualization for native code • Waba - Virtual machine for small devices, similar to Java • Warren Abstract Machine - Prolog, CSC GraphTalk • Z-machine - Z-Code •
OS-level virtualization software
• • • • • •
OpenVZ FreeVPS Linux-VServer FreeBSD Jails Solaris Containers AIX Workload Partitions
Zend Engine - PHP
Dept. of Computer Engineering, ICOER, Pune.
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Virtual Machine VMware Architecture
All the vm app work in complete isolation from each other. The app is given the impression that it is working on the same platform as a normal process the user does not come out to know any diff exits in the platform or the execution.
Dept. of Computer Engineering, ICOER, Pune.
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Virtual Machine VMware Workstation
VMware Workstation is a virtual machine software suite for x86 and x86-64 computers from VMware, a division of EMC Corporation. This software suite allows users to set up multiple x86 and x86-64 virtual computers and to use one or more of these virtual machines simultaneously with the hosting operating system. Each virtual machine instance can execute its own guest operating system, such as Windows, Linux, BSD variants, or others. In simple terms, VMware Workstation allows one physical machine to run multiple operating systems simultaneously. Other VMware products help manage or migrate VMware virtual machines across multiple host machines. Besides bridging to existing host network adapters, CD-ROM devices, hard disk drives, and USB devices, VMware Workstation also provides the ability to simulate some hardware. For example, it can mount an ISO file as a CD-ROM, and .vmdk files as hard disks; and can configure its network adapter driver to use network address translation (NAT) through the host machine rather than bridging through it (which would require an IP address for each guest machine on the host network). VMware Workstation also allows the testing of live CDs without first burning them onto physical discs or rebooting the computer. One can also take multiple successive snapshots of an operating system running under VMware Workstation. Each snapshot allows you to roll back the virtual machine to the saved status at any time. The ability to use multiple snapshots makes VMware Workstation useful as a tool for salespersons demonstrating complex software products, and for developers setting up virtual development or test environments. VMware Workstation includes the ability to designate multiple virtual machines as a team which administrators can then power on and off, suspend, and resume as a single object — making it particularly useful for testing client-server environments.
Known issues
Known limitations of VMware Workstation, as of June, 2008, include the following: Hardware support VMware virtual machines do not directly support FireWire.[10] VMware Workstation cannot use more than 2 CPUs (or cores) per virtual machine. This means that a single virtual machine cannot use the full power of the underlying hardware on machines with the total number of cores greater than 2 (Quad Core 2, or 2 x Core 2). This is true also for the last version 6.5. • VMware virtual machines provide only experimental support for 3D hardware acceleration, via Microsoft's Direct3D 8 API.[11][12] A video has appeared on YouTube that demonstrates several 3D-accelerated games running under VMware Fusion and Mac OS X. The release notes for Fusion beta 2 include a list of 3D-accelerated computer games that can run within Windows XP-based virtual machines. In version 6.5, Direct3D 9.0 API support (up to Shader Model 2.0) is provided on Windows XP guests and on any host OS. • Five-button mouse is supported in version 6.5.[citation needed]
• •
Dept. of Computer Engineering, ICOER, Pune.
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Virtual Machine
Additionally, when using VMware Workstation in an environment using Media Access Control (MAC) addresses as unique identifiers (UID), one should (and often must) manually configure the MAC address for each virtual machine in order to ensure uniqueness (for example, in an environment in which network switches implement MAC security; or in an environment in which Altiris products use the MAC address as the UID). In such a situation, disabling all networks/adapters other than "bridged" and editing each virtual machine's .vmx file to change "ethernet0.address" to a unique MAC and "ethernet0.addresstype" to "static" will help.
•
OS support 64-bit Solaris 10 1/06 (Update 1) and Solaris 10 6/06 (Update 2) fail with a triple fault on Core 2 generation processors (this includes processors codenamed Merom, Woodcrest, and Conroe). A Sun Microsystems blog has published a workaround for this issue. Network protocols VMware Workstation can swallow CPU interrupts, making maintenance of accurate time difficult.[13] Network Time Protocol (NTP) servers should not be run under VMware. Path traversal vulnerability In February 2008, CoreSecurity.com discovered a vulnerability in the Shared Folders function within several VMware products, including Workstation. A user logged onto a guest VM running in VMware Workstation could gain read/write access to the host system by specifying a pathname with the ".." substring.[14][15] However, the host is only vulnerable if the shared folders are turned on and at least one host folder is set for sharing. This vulnerability was fixed in VMware Workstation versions 5.5.6 and 6.0.3.
VMware Tools
VMware Tools is a package with drivers and other software that can be installed in guest operating systems to increase their performance.
Virtual appliance
A virtual appliance is a minimalist virtual machine image designed to run under some sort of virtualization technology (like VMware Workstation, Citrix XenServer, VirtualBox or many others).
Dept. of Computer Engineering, ICOER, Pune.
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Virtual Machine
Virtual appliances are a subset of the broader class of software appliances. Like software appliances, virtual appliances are aimed to eliminate the installation, configuration and maintenance costs associated with running complex stacks of software. A key concept that differentiates a virtual appliance from a virtual machine is that a virtual appliance is a fully pre-installed and pre-configured application and operating system environment whereas a virtual machine is, by itself, without application software. Typically a virtual appliance will have a web interface to configure the inner workings of the appliance. A virtual appliance is usually built to host a single application, and so represents a new way of deploying network applications. As an example, the MediaWiki software that powers Wikipedia is available as a virtual appliance.[1]. This appliance contains all the necessary software, including operating system, database and MediaWiki, to run a wiki installation as a "black box".
THE FUTURE OF VIRTUAL MACHINES
Although hardware-level virtualization went from being widely used during the 1970s to near extinction in the 1980s, it has come back in a strong way. The success of VMware’s products in the commercial marketplace, together with recent hardware support for virtualization such as Intel’s Vanderpool technology and extensions to IBM’s Power architecture, indicate that it is a technology just now beginning to be fully realized and that it is here to stay.
Dept. of Computer Engineering, ICOER, Pune.
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Virtual Machine
Computing trends indicate that the data center of the future will likely include a hardwarelevel virtualization layer and a control system. Services will run in virtual machines and will be mapped onto available hardware resources. Not only will this greatly ease the management of data centers, it will also ease the handling of new hardware, as well as failed hardware. The failure of a single physical box will reduce the pool of available resources, not the availability of a particular service. Similarly, virtual machine technology will be used to allow aggressive innovation in the area of system software, providing the ability to maintain backward compatibility. Virtual machines will allow for the support of old applications, as well as the current versions, and will test the deployment of new versions that are all based on the same hardware. One consequence of Moore’s law of semiconductor growth has been the exponential increase in the performance of computing systems. The overhead of a well-tuned hardware virtualization system is extremely small compared with the performance increase. This means that the computing industry can, for only a few percentage points of performance, realize the huge benefits of hardware-level virtualization. Such benefits include the management of both the hardware and the software that runs in virtual machines—currently a large expense in modern computing environments.
Conclusion
In conclusion I would like to say that Virtual Machine is the prefect tool for the 21st century to advance and become more powerful then it was ever before. A virtual-machine system is a perfect vehicle for operating-systems research and development. By making the applications platform independent and having multiple Os in a single machine have made the engineers to use the full of its resources and manage it efficiently and give faster and better performance.
Dept. of Computer Engineering, ICOER, Pune.
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Virtual Machine
Bibliography
www.google.com www.wikipedia.com
Dept. of Computer Engineering, ICOER, Pune.
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Faced with large, heterogeneous information systems and the accelerated rate of technological innovation, software engineers are beginning to rediscover the benefits of targeting virtual machines. The name of the game in software development is return on investment. Companies want to invest money in software that will be useful long enough for the resources spent to be justified. Porting a software package from one platform to another is costly and, depending on the number of platforms supported, can prove to be a Sisyphean nightmare. The worst-case scenario occurs when business logic is stranded on an aging system. Due to historical forces, a large base of code may end up on an obsolete platform that no one wants to deal with. The people who wrote the original code have either quit or been promoted and don't remember anything (sometimes intentionally). The source code has been transformed by time into an encrypted historical artifact that will require years of work by researchers to decipher. If the language and tools used to develop the initial code are linked to the original platform, porting may be out of the question. In pathological cases, the code may be so obscure and illegible that maintenance engineers are too scared to touch anything. I'm sure Y2K programmers are familiar with this type of imbroglio. The only recourse may be a complete rewrite and this is an extremely expensive alternative, fraught with all sorts of dangers and hidden costs. This is the kind of situation CIOs lose sleep over. Using a virtual machine offers a degree of insurance against this kind of thing happening. When confronted with a new hardware platform or operating system, the only application that needs to be ported is the virtual machine itself. If a virtual machine is, say, 100,000 lines of code, you might think that actually porting the code is a bad investment. 100,000 lines of code is not a trivial porting job. However, let's say that the virtual machine runs an application suite that consists of 11 million lines of code. Suddenly, porting the virtual machine is not such a bad deal because the alternative would be to port the 11 million lines of application code. Don't think that this isn't realistic. I once visited an automobile insurance company that had around 30 million lines of application code.
Dept. of Computer Engineering, ICOER, Pune.
1
Virtual Machine
OBJECTIVE:
Objective was to build a virtual machine that satisfied three criterion. In order of priority, these are: 1. Portability 2. Simplicity 3. Performance Portability is the most important feature because being able to work with a uniform software interface, across multiple platforms, is the primary benefit of using a virtual machine. If you can't port a virtual machine, then you're stuck with a given platform, in which case you might as well use tools that compile to the native machine encoding. Portability is also the most important priority in the sense that I had to make sacrifices in terms of simplicity and performance in order to achieve it. There is rarely a solution that is ever optimal under all conditions in software engineering. One way of boosting performance would be to make heavy use of assembly code. However, using an assembler does not necessarily guarantee faster program execution. In order to be able to justify using an assembler, the programmer has to have an intimate knowledge of both the assembly code a compiler generates and the kind of optimizations it performs. The goal is to be able to write faster assembly code than the compiler can. This requires a certain amount of vigilance and skill because, in most cases, the optimizer in a C compiler can do a better job than the average programmer. Another problem with using assembly language is that it ties your code to the hardware you're working on. To port the code to new hardware, you'll need to rewrite every single line of assembly code. This can turn out to be much more work than you think. Again, in the effort to maintain a certain degree of portability, I opted out of low-level, high-performance assembly coding and wrote everything in ANSI C. simplicity has priority over performance by virtue of my desire to make the code maintainable. A year from now, I would like to be able to modify my code without having to call in a team of archaeologists. Code that is optimized for performance can become very brittle and resistant to change. Developers writing high-performance C code will often use all sorts of misleading and confusing conventions, like bitwise shifting to divide by 2. What is produced is usually illegible by anyone but the original developer, and given enough time even the original developer may forget what he had done and why he had done it. In an extreme case, a programmer who has created a mess and is too scared to clean it up may opt to quit and go work somewhere else. I've heard people refer to this as "the final solution" or "calling in for air support and pulling out."
Dept. of Computer Engineering, ICOER, Pune.
2
Virtual Machine
Run-time Systems
A run-time system is an environment in which computer programs execute. A run-time system provides everything a program needs in order to run. For example, a run-time system is responsible for allocating memory for an application, loading the application into the allocated memory, and facilitating the execution of the program's instructions. If the program requests services from the underlying operating system through the invocation of system calls, the runtime system is in charge of handling those service requests. For instance, if an application wants to perform file I/O, the run-time system must offer a mechanism to communicate with the disk controller and provide read/write access. There are different kinds of run-time systems. One way to classify run-time systems is to categorize them based on how they execute a program's instructions. For programs whose instructions use the processor's native machine encoding, the run-time system consists of a tightly knit collaboration between the computer's processor and the operating system. The processor provides a mechanism for executing program instructions. The CPU does nothing more than fetch instructions from memory, which are encoded as numeric values, and perform the actions corresponding to those instructions. The operating system implements the policy side of a computer's native run-time system. The CPU may execute instructions, but the operating system decides how, when, and where things happen. Think of the operating system as a fixed set of rules the CPU has to obey during the course of instruction execution. Thus, for programs written in native machine instructions, the computer itself is the runtime system. Program instructions are executed at the machine level, by the physical CPU, and the operating system manages how the execution occurs. This type of run-time system involves a mixture of hardware and software. Programs whose instructions are not directly executed by the physical processor require a run-time system that consists entirely of software. In such a case, the program's instructions are executed by a virtual machine. A virtual machine is a software program that acts like a computer. It fetches and executes instructions just like a normal processor. The difference is that the processing of those instructions happens at the software level instead of the hardware level. A virtual machine also usually contains facilities to manage the path of execution and to offer an interface to services normally provided by the native operating system. A virtual machine is defined by a specification. A virtual machine is not a particular software implementation, but rather a set of rules. These rules form a contract that the engineer, who builds an instantiation of the virtual machine, must honor. A virtual machine can be implemented in any programming language on any hardware platform, as long as it obeys the specification. You could create a version of the HEC virtual machine on an OS/390 using APL if you really wanted to. This is what makes the idea of a virtual machine so powerful. You can run HEC executables, without recompilation, anywhere there is a run-time system that obeys the specification.
Dept. of Computer Engineering, ICOER, Pune.
3
Virtual Machine Definitions
Virtual machine was originally defined by Popek and Goldberg as "an efficient, isolated duplicate of a real machine". Current use includes virtual machines which have no direct correspondence to any real hardware. Virtual machines are separated into 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 contrast, a process virtual machine is designed to run a single program, which means that it supports a single process. 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. Example: A program written in Java receives services from the Java Runtime Environment (JRE) software by issuing commands to, and receiving the expected results from, the Java software. 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 be tailored.
Dept. of Computer Engineering, ICOER, Pune.
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Virtual Machine System virtual machines
System virtual machines (sometimes called hardware virtual machines) allow the sharing of the underlying physical machine resources between different virtual machines, each running its own operating system. The software layer providing the virtualization is called a virtual machine monitor or hypervisor. 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
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). 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. Another use is to sandbox an OS that is not trusted, possibly because it is a system under development. Virtual machines have other advantages for OS development, including better debugging access and faster reboots.[2] Alternate techniques such as Solaris Zones provides a level of isolation within a single operating system. This does not have isolation as complete as a VM. A kernel exploit in a system with multiple zones will affect all zones. Achieving the same goal in a virtual machine implementation would require exploiting a weakness in the hypervisor. A hypervisor typically has a smaller "attack surface" than a complete operating system, making this more challenging. Further, a kernel exploit in a VM guest would not affect other VMs on the host, just as a successful intrusion into one zone would not necessarily affect other zones. 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, LinuxVServer, chroot jail, and OpenVZ. These provide some form of encapsulation of processes within an operating system. These technologies have the advantages of being more resourceefficient than full virtualization and having better observability into multiple guests
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simultaneously; the disadvantage is that, generally, they can only run a single operating system and a single version/patch level 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. However, Sun Microsystems has enhanced Solaris Zones to allow some zones to behave like Solaris 8 or Solaris 9 systems by adding a system call translator
Process virtual machines
A process VM, sometimes called an application virtual machine, runs as a normal application inside an OS and supports a single process. It is created when that process is started
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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. A process VM provides a high-level abstraction — that of a high-level programming language (compared to the low-level ISA abstraction of the system VM). Process VMs are implemented using an interpreter; performance comparable to compiled programming languages is achieved by the use of just-in-time compilation. This type of VM has become popular with the Java programming language, which is implemented using the Java virtual machine. Another example is the .NET Framework, which runs on a VM called the Common Language Runtime. 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). Examples are PVM (Parallel Virtual Machine) and MPI (Message Passing Interface). 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".
List of hardware with virtual machine support Dept. of Computer Engineering, ICOER, Pune.
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Alcatel-Lucent 3B20D/3B21D emulated on commercial off-the-shelf computers with 3B2OE or 3B21E system • 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. • Freescale PowerPC MPC8572 and MPC8641D • IBM System/370, System/390, and zSeries mainframes • Intel VT (formerly code-named Vanderpool) • Sun Microsystems sun4v (UltraSPARC T1 and T2) -- utilized by Logical Domains
• • • • •
HP vPAR and cell based nPAR GE Project MAC then Honeywell Multics systems Honeywell 200/2000 systems Liberator replacing IBM 14xx systems, Level 62/64/66 IBM System/360 Model 145 Hardware emulator for Honeywell 200/2000 systems RCA Spectra/70 Series emulated IBM System/360 NAS CPUs emulated IBM and Amdahl machines Honeywell Level 6 minicomputers emulated predecessor 316/516/716 minis Xerox Sigma 6 CPUs were modified to emulate GE/Honeywell 600/6000 systems
GCOS
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List of virtual machine software
Process (Application) virtual machine System (Hardware) virtual machine 8
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software
•
software[clarification needed]
Common Language Infrastructure - C#, • ATL (A MTL Virtual Machine) Visual Basic .NET, J#, C++/CLI (formerly • Bochs, portable open source x86 and Managed C++) AMD64 PCs emulator • Dalvik virtual machine - part of the • CoLinux Open Source Linux inside Android mobile phone platform Windows • Dis - Inferno operating system and its • Denali, uses paravirtualization of x86 Limbo programming language for running para-virtualized PC operating • Dosbox systems. • EiffelStudio for the Eiffel programming • FAUmachine language • Hercules emulator, free System/370, • Erlang programming language ESA/390, z/Mainframe • Forth virtual machine - Forth • KVM • Glulx - Glulx, Z-code • LilyVM is a lightweight virtual • Hec - Hasm Assembler machineAn introduction • Java Virtual Machine - Java, Nice, • Logical Domains NetREXX • Microsoft Virtual PC and Microsoft • Low Level Virtual Machine (LLVM) - Virtual Server currently C, C++, Stacker • OKL4 from Open Kernel Labs • Lua • Oracle VM • Macromedia Flash Player - SWF • OVPsim [1] is a freely available virtual • MMIX - MMIXAL platform simulator designed to simulate • Neko virtual machine - currently Neko complex multiprocessor systems at very high and haXe speeds • O-code machine - BCPL • Parallels Workstation, provides • p-code machine - Pascal virtualization of x86 for running unmodified • Parrot - Perl 6 PC operating systems • Perl virtual machine - Perl • Parallels Desktop for Mac, provides • CPython - Python virtualization of x86 for running virtual • YARV - Ruby MRI machines on Mac OS X or higher • Rubinius - Ruby • QEMU, is a simulator based on a • ScummVM - Scumm virtual machine. • SECD machine - ISWIM, Lispkit Lisp • SheepShaver. • Sed the stream-editor can also be seen • Simics as a VM with 2 storage spaces. • Sun xVM • Smalltalk virtual machine - Smalltalk • SVISTA • SQLite virtual machine - SQLite • Trango Virtual Processors opcodes • twoOStwo • Squeak virtual machine - Squeak • User-mode Linux • SWEET16 • VirtualBox • Tamarin (JavaScript engine) • Virtual Iron (Virtual Iron 3.1) ActionScript VM in Flash 9 • VM from IBM • TrueType virtual machine - TrueType • VMware (ESX Server, Fusion, Virtual • Valgrind - checking of memory Server, Workstation, Player and ACE) accesses and leaks in x86/x86-64 code under • vSMP Foundation (From ScaleMP)
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Linux
•
Virtual Processor (VP) from Tao Group
• •
Xen IBM POWER SYSTEMS
(UK).
• VX32 virtual machine - applicationlevel virtualization for native code • Waba - Virtual machine for small devices, similar to Java • Warren Abstract Machine - Prolog, CSC GraphTalk • Z-machine - Z-Code •
OS-level virtualization software
• • • • • •
OpenVZ FreeVPS Linux-VServer FreeBSD Jails Solaris Containers AIX Workload Partitions
Zend Engine - PHP
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All the vm app work in complete isolation from each other. The app is given the impression that it is working on the same platform as a normal process the user does not come out to know any diff exits in the platform or the execution.
Dept. of Computer Engineering, ICOER, Pune.
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VMware Workstation is a virtual machine software suite for x86 and x86-64 computers from VMware, a division of EMC Corporation. This software suite allows users to set up multiple x86 and x86-64 virtual computers and to use one or more of these virtual machines simultaneously with the hosting operating system. Each virtual machine instance can execute its own guest operating system, such as Windows, Linux, BSD variants, or others. In simple terms, VMware Workstation allows one physical machine to run multiple operating systems simultaneously. Other VMware products help manage or migrate VMware virtual machines across multiple host machines. Besides bridging to existing host network adapters, CD-ROM devices, hard disk drives, and USB devices, VMware Workstation also provides the ability to simulate some hardware. For example, it can mount an ISO file as a CD-ROM, and .vmdk files as hard disks; and can configure its network adapter driver to use network address translation (NAT) through the host machine rather than bridging through it (which would require an IP address for each guest machine on the host network). VMware Workstation also allows the testing of live CDs without first burning them onto physical discs or rebooting the computer. One can also take multiple successive snapshots of an operating system running under VMware Workstation. Each snapshot allows you to roll back the virtual machine to the saved status at any time. The ability to use multiple snapshots makes VMware Workstation useful as a tool for salespersons demonstrating complex software products, and for developers setting up virtual development or test environments. VMware Workstation includes the ability to designate multiple virtual machines as a team which administrators can then power on and off, suspend, and resume as a single object — making it particularly useful for testing client-server environments.
Known issues
Known limitations of VMware Workstation, as of June, 2008, include the following: Hardware support VMware virtual machines do not directly support FireWire.[10] VMware Workstation cannot use more than 2 CPUs (or cores) per virtual machine. This means that a single virtual machine cannot use the full power of the underlying hardware on machines with the total number of cores greater than 2 (Quad Core 2, or 2 x Core 2). This is true also for the last version 6.5. • VMware virtual machines provide only experimental support for 3D hardware acceleration, via Microsoft's Direct3D 8 API.[11][12] A video has appeared on YouTube that demonstrates several 3D-accelerated games running under VMware Fusion and Mac OS X. The release notes for Fusion beta 2 include a list of 3D-accelerated computer games that can run within Windows XP-based virtual machines. In version 6.5, Direct3D 9.0 API support (up to Shader Model 2.0) is provided on Windows XP guests and on any host OS. • Five-button mouse is supported in version 6.5.[citation needed]
• •
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Additionally, when using VMware Workstation in an environment using Media Access Control (MAC) addresses as unique identifiers (UID), one should (and often must) manually configure the MAC address for each virtual machine in order to ensure uniqueness (for example, in an environment in which network switches implement MAC security; or in an environment in which Altiris products use the MAC address as the UID). In such a situation, disabling all networks/adapters other than "bridged" and editing each virtual machine's .vmx file to change "ethernet0.address" to a unique MAC and "ethernet0.addresstype" to "static" will help.
•
OS support 64-bit Solaris 10 1/06 (Update 1) and Solaris 10 6/06 (Update 2) fail with a triple fault on Core 2 generation processors (this includes processors codenamed Merom, Woodcrest, and Conroe). A Sun Microsystems blog has published a workaround for this issue. Network protocols VMware Workstation can swallow CPU interrupts, making maintenance of accurate time difficult.[13] Network Time Protocol (NTP) servers should not be run under VMware. Path traversal vulnerability In February 2008, CoreSecurity.com discovered a vulnerability in the Shared Folders function within several VMware products, including Workstation. A user logged onto a guest VM running in VMware Workstation could gain read/write access to the host system by specifying a pathname with the ".." substring.[14][15] However, the host is only vulnerable if the shared folders are turned on and at least one host folder is set for sharing. This vulnerability was fixed in VMware Workstation versions 5.5.6 and 6.0.3.
VMware Tools
VMware Tools is a package with drivers and other software that can be installed in guest operating systems to increase their performance.
Virtual appliance
A virtual appliance is a minimalist virtual machine image designed to run under some sort of virtualization technology (like VMware Workstation, Citrix XenServer, VirtualBox or many others).
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Virtual appliances are a subset of the broader class of software appliances. Like software appliances, virtual appliances are aimed to eliminate the installation, configuration and maintenance costs associated with running complex stacks of software. A key concept that differentiates a virtual appliance from a virtual machine is that a virtual appliance is a fully pre-installed and pre-configured application and operating system environment whereas a virtual machine is, by itself, without application software. Typically a virtual appliance will have a web interface to configure the inner workings of the appliance. A virtual appliance is usually built to host a single application, and so represents a new way of deploying network applications. As an example, the MediaWiki software that powers Wikipedia is available as a virtual appliance.[1]. This appliance contains all the necessary software, including operating system, database and MediaWiki, to run a wiki installation as a "black box".
THE FUTURE OF VIRTUAL MACHINES
Although hardware-level virtualization went from being widely used during the 1970s to near extinction in the 1980s, it has come back in a strong way. The success of VMware’s products in the commercial marketplace, together with recent hardware support for virtualization such as Intel’s Vanderpool technology and extensions to IBM’s Power architecture, indicate that it is a technology just now beginning to be fully realized and that it is here to stay.
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Computing trends indicate that the data center of the future will likely include a hardwarelevel virtualization layer and a control system. Services will run in virtual machines and will be mapped onto available hardware resources. Not only will this greatly ease the management of data centers, it will also ease the handling of new hardware, as well as failed hardware. The failure of a single physical box will reduce the pool of available resources, not the availability of a particular service. Similarly, virtual machine technology will be used to allow aggressive innovation in the area of system software, providing the ability to maintain backward compatibility. Virtual machines will allow for the support of old applications, as well as the current versions, and will test the deployment of new versions that are all based on the same hardware. One consequence of Moore’s law of semiconductor growth has been the exponential increase in the performance of computing systems. The overhead of a well-tuned hardware virtualization system is extremely small compared with the performance increase. This means that the computing industry can, for only a few percentage points of performance, realize the huge benefits of hardware-level virtualization. Such benefits include the management of both the hardware and the software that runs in virtual machines—currently a large expense in modern computing environments.
Conclusion
In conclusion I would like to say that Virtual Machine is the prefect tool for the 21st century to advance and become more powerful then it was ever before. A virtual-machine system is a perfect vehicle for operating-systems research and development. By making the applications platform independent and having multiple Os in a single machine have made the engineers to use the full of its resources and manage it efficiently and give faster and better performance.
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Bibliography
www.google.com www.wikipedia.com
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