Virtual Machines

• Separates the hardware interface from the OS
  • the OS still thinks it is using the hardware directly

Overhead

• Depends on the workload
• User-level processor-bound programs have zero overhead
  • Because OS is rarely invoked
• I/O intensive → OS intensive
  • Executes many system calls
  • Can result in high overhead
• I/O intensive is also I/O bound
  • Low processor utilization since waiting for I/O
  • Processor virtualization can be hidden because something else is slower

Uses

• Increased Security
  • Takes a portion of the operating system that provides hardware security and separates it
  • Operating systems aren’t perfect, so they can’t always protect you
  • Allows for increased scrutiny on security critical components
• Managing software
  • Provide an abstraction that can run the complete SW stack
  • Can also run old OSs or beta OSs
• Managing Hardware
  • Allows separate SW stacks to run independently yet share HW
  • A single server can be used my multiple clients isolated