Definitions

• Host Operating System:
  • The operating system actually running on the hardware
  • Together with virtualization layer, it simulates environment for …
• Guest Operating System:
  • The operating system running in the simulated environment
  • i.e., the one we are trying to isolate

Cloud virtualization

• Decouple [OS, service] pair from hardware
• Multiplex lightly-used services on common host hardware
• Migrate services from host to host as needed
• Introduce new [OS, service] pairs as needed
  • Commissioning new services
  • Testing upgrades of existing services
  • Experimental usage
  • …

Virtual-machine concept provides complete protection of system resources

• Each virtual machine is isolated from all other virtual machines.
• However, limited sharing of resources

Virtual-machine system is a good vehicle for operating-systems research and development.

• System development is done on the virtual machine does not disrupt normal operation
• Multiple concurrent developers can work at same time

The virtual machine concept is difficult to implement due to the effort required to provide an exact duplicate to the simulated machine.

Some hardware architectures or features are impossible to virtualize

• Certain registers or state not exposed
• Unusual devices and device control
• Clocks, time, and real-time behavior

Solution – drivers or tools in guest OS

• VMware Tools
• Xen configuration options in Linux build