Survey of Virtual Machine Research

Principles

• virtual machine systems: simulators for multiple copies of a machine on itself.
• virtual machine (VM): the simulated machine.
• virtual machine monitor (VMM): the simulator software.
• Principal characteristics of the third-generation architectures for which virtual machine systems were originally developed was the dual-state hardware organization with a privileged and non-privileged mode.
• privileged software nucleus (kernel)
• extended machine: set of non-privileged instructions together with the supervisory calls.

Performance

• Extra resources needed: main memory, processor cycles.
• Sources of overhead:
  • Maintaining the status of the virtual processor.
  • Support of privileged instructions.
  • Support of paging within virtual machines.
  • Console functions.
• A problem: resource allocation algorithms in operating system (these are meant for managing real resources, but the virtual resources may not correspond precisely to real resources).

Practice (example uses)

• Privileged software development, test and diagnostic functions, multiple operating system execution concurrently with production uses of the system.
• Retrofit old operating systems with new features.
• Improved testing of privileged software.
• Testing of computer network software on a single physical machine.
• Debugging and performance monitoring tools.
• Software reliability through isolation.
• Data security.