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Virtual Machines. Kenneth Westrom ELEC-6620. Overview. Intro Abstraction versus Virtualization Interfaces Process Virtual Machines System Virtual Machines Conclusion References. Intro. Virtual machines are “an efficient, isolated duplicate of a real machine” -Popek and Goldberg

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Virtual machines

Virtual Machines

Kenneth Westrom


Westrom: Virtual Machines


  • Intro

  • Abstraction versus Virtualization

  • Interfaces

  • Process Virtual Machines

  • System Virtual Machines

  • Conclusion

  • References

Westrom: Virtual Machines


  • Virtual machines are “an efficient, isolated duplicate of a real machine”

    -Popek and Goldberg

    Popek and Goldberg introduced conditions for computer architecture to efficiently support system virtualization.

Westrom: Virtual Machines

Abstraction versus virtualization
Abstraction versus Virtualization

  • Computer architecture benefits from Abstraction

    • Well-defined interfaces for hardware and software to use

      • Hard Drives, Networking, I/O devices

    • Limits based on the hardware implementation

  • Virtualization

    • Maps interfaces and

      resources to various hardware,

      even different architectures

Westrom: Virtual Machines

Architecture interfaces
Architecture Interfaces

  • Virtualization can take place at these junctures

    • ISA – Instruction Set Architecture

    • ABI – Application Binary Interface

    • API – Application Programming Interface

Westrom: Virtual Machines

Process virtual machines
Process Virtual Machines

  • Also known as Application VM

  • Virtualization below the API or ABI, providing virtual resources to a single process executed on a machine

  • Created for the process alone, destroyed when process finishes

Westrom: Virtual Machines

Process vm continued
Process VM, continued

  • Multiprogrammed systems

    • Each application is given effectively separate access to resources, managed by the OS

  • Emulators and translators

    • Executes program binaries compiled for different instruction sets.

    • Slower, requiring hardware interpretation

      • Optimization through storing blocks of converted code for repeated execution

Westrom: Virtual Machines

Process vm continued1
Process VM, continued

  • Optimizers, Same ISA

    • Perform code optimization during translation and execution

  • High-level-language VM

    • Cross-platform compatibiltiy

    • Programs written for an abstract machine, which is mapped to real hardware through a virtual machine

      • Sun Microsystems Java VM

      • Microsoft Common Language Infrastructure, .NET framework

Westrom: Virtual Machines

System virtual machines
System Virtual Machines

  • Virtualized hardware below the ISA

  • Single host can run multiple isolated operating systems

    • Servers running different operating systems

    • Isolation between concurrent systems, security

  • Hardware

    Managed by the

    VMM – Virtual

    Machine Manager

Westrom: Virtual Machines

System vm continued
System VM, continued

  • Classically, VMM runs on bare hardware, directly interacting with resources,

    • Intercepts and interprets guest OS actions

  • Hosted VM

    • Installed application that relies on the OS to access hardware, using same ISA

  • Whole System VM

    • Emulate both application and system code for different ISAs

      • Classically: Virtual PC, run windows on old Mac hardware

Westrom: Virtual Machines

System vm continued1
System VM, continued

  • Multiple operating systems on one machine

    • Processor/resources timeshared

    • Quality-of-service isolation

  • Testing of insecure or questionable software and systems

    • Better debugging

Westrom: Virtual Machines


  • Virtual Machines can be useful in crossing boundaries based on ISA differences

  • Hardware consolidation

  • Cross-platform compatability

Westrom: Virtual Machines


  • Smith, Daniel E.; Nair, Ravi. "The Architecture of Virtual Machines". Computer 38 (5): 32–38. IEEE Computer Society.

  • Wikipedia, “Virtual Machine”.

Westrom: Virtual Machines