Editing Virtual machine (section)

== Virtualization techniques ==
{{Main|Full virtualization}}
[[File:Hardware Virtualization (copy).svg|thumb|Logical diagram of full virtualization]]

=== Full virtualization ===
In full virtualization, the virtual machine simulates enough hardware to allow an unmodified "guest" OS (one designed for the same [[instruction set]]) to be run in isolation. This approach was pioneered in 1966 with the IBM [[CP-40]] and [[CP-67]], predecessors of the [[VM (Operating system)|VM]] family.

Examples outside the mainframe field include [[Parallels Workstation]], [[Parallels Desktop for Mac]], [[VirtualBox]], [[Virtual Iron]], [[Oracle VM]], [[Microsoft Virtual PC|Virtual PC]], [[Microsoft Virtual Server|Virtual Server]], [[Hyper-V]], [[VMware Fusion]], [[VMware Workstation]], [[VMware Server]] (discontinued, formerly called GSX Server), [[VMware ESXi]], [[QEMU]], [[Adaptive Domain Environment for Operating Systems|Adeos]], Mac-on-Linux, Win4BSD, [[Win4Lin|Win4Lin Pro]], and Egenera vBlade  technology.

==== Hardware-assisted virtualization ====
{{Main|Hardware-assisted virtualization}}

In hardware-assisted virtualization, the hardware provides architectural support that facilitates building a virtual machine monitor and allows guest OSes to be run in isolation.<ref name="Uhlig_2005"/>
Hardware-assisted virtualization was first introduced on the IBM System/370 in 1972, for use with [[VM (operating system)|VM/370]], the first virtual machine operating system offered by IBM as an official product.<ref>Randal, A. (2019). The Ideal Versus the Real: Revisiting the History of Virtual Machines and Containers.</ref>

In 2005 and 2006, [[Intel]] and [[Advanced Micro Devices|AMD]] provided additional hardware to support virtualization. Sun Microsystems (now [[Oracle Corporation]]) added similar features in their [[SPARC T3|UltraSPARC T-Series]] processors in 2005.  Examples of virtualization platforms adapted to such hardware include [[Kernel-based Virtual Machine|KVM]], [[VMware Workstation]], [[VMware Fusion]], [[Hyper-V]], [[Windows Virtual PC]], [[Xen]], [[Parallels Desktop for Mac]], [[Oracle VM Server for SPARC]], [[VirtualBox]] and [[Parallels Workstation]].

In 2006, first-generation 32- and 64-bit x86 hardware support was found to rarely offer performance advantages over software virtualization.<ref name="Adams_2006"/>

=== OS-level virtualization ===
{{Main|OS-level virtualization}}

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" operating system environments share the same running instance of the operating system as the host system.  Thus, the same [[operating system kernel]] is also used to implement the "guest" environments, and applications running in a given "guest" environment view it as a stand-alone system. The pioneer implementation was [[FreeBSD jail]]s; other examples include [[Docker (software)|Docker]], [[Solaris Containers]], [[OpenVZ]], [[Linux-VServer]], [[LXC]], AIX [[Workload Partitions]], Parallels Virtuozzo Containers, and iCore Virtual Accounts.