Techniques/levels/Types of virtualization


Full Virtualization:
In Full Virtualization, Virtual Machine simulated enough hardware to allow unmodified guest OS to run.

examples:

  • Adeos
  • Mac-on-Linux
  • Parallels Desktop for Mac
  • Parallels Workstation
  • VMware Workstation
  • VMware Server (formerly GSX Server)
  • VirtualBox
  • Win4BSD
  • Win4Lin Pro.


Hardware-assisted virtualization


First implemented on the IBM System/370, hardware-assisted virtualization is a platform virtualization approach that enables efficient full virtualization using help from hardware capabilities, primarily from the host processors. Full virtualization is used to simulate a complete hardware environment, or virtual machine, in which an unmodified guest operating system (using the same instruction set as the host machine) executes in complete isolation. Hardware-assisted virtualization was recently (2006) added to x86 processors (Intel VT-x or AMD-V).

Examples
of virtualization platforms adapted to such hardware include

  • Linux KVM
  • VMware Workstation
  • VMware Fusion
  • Microsoft Virtual PC
  • Xen
  • Parallels Desktop for Mac
  • VirtualBox
  • Parallels Workstation.


Paravirtualization (Hypervisors)


It is a partial Virtualization, but is somehow similar to Full Virtualization. In this the guest OS needs to be modified to work. Because Guest OS communicates with Physical resources using special API's.

Example:

  • Xen
  • KVM

Operating System Level Virtualization (VE's Containers):
In OS Level Virtualization a physical server is virtualized at the operating system level, enabling multiple isolated and secure virtualized servers to run on a single physical server. The "guest" OS environments share the same OS as the host system – i.e. the same OS kernel is used to implement the "guest" environments. Applications running in a given "guest" environment view it as a stand-alone system.

Examples:

  • Solaris Containers
  • OpenVZ
  • Linux-VServer
  • AIX Workload Partitions
  • Parallels Virtuozzo Containers (Based on openVZ)
  • iCore Virtual Accounts.