Virtual machines and hypervisors

Emulation of a particular (virtual) hardware with the existing one (real).

Hosted virtualization

The hypervisor is a process of a given OS (host).

The VM runs inside the virtualizer (guest OS).

Bare-metal virtualization

The hypervisor runs on top of the host hardware.

Execution of virtual machines

A common approach for hosted virtualization.

Software-based virtualization.

• Direct execution of guest user-mode code.

• Binary, on-the-fly translation of privileged code (full virtualization).

  • Guest OS kernels remain unchanged.

  • No direct access to the host hardware.

Hardware-assisted virtualization (bare-metal).

• Full virtualization.

• There is a ring -1 below ring 0.

  • Hypervisor (or Virtual Machine Monitor, VMM).

• It can virtualize hardware for many ring 0 kernels.

  • There is no need for binary translation.

  • Guest OS runs faster.