Editing Hypervisor (section)

== Classification ==
[[File:Hyperviseur.svg|thumb|right|upright=1.8|Type-1 and type-2 hypervisors]]

In his 1973 thesis, "Architectural Principles for Virtual Computer Systems," [[Robert P. Goldberg]] classified two types of hypervisor:<ref name="goldberg1973" />

; Type-1, native or bare-metal hypervisors
: These hypervisors run directly on the host's hardware to control the hardware and to manage guest operating systems. For this reason, they are sometimes called [[Bare machine|bare-metal]] hypervisors. The first hypervisors, which IBM developed in the 1960s, were native hypervisors.<ref>{{cite web |first=Shannon |last=Meier |title=IBM Systems Virtualization: Servers, Storage, and Software |year=2008 |pages=2, 15, 20 |url=http://www.redbooks.ibm.com/redpapers/pdfs/redp4396.pdf |access-date=2015-12-22}}</ref> These included the test software [[SIMMON]] and the [[CP/CMS]] operating system, the predecessor of IBM's [[VM (operating system)|VM family]] of [[virtual machine]] [[operating systems]]. Examples of Type-1 hypervisor include [[Hyper-V]], [[Xen]] and [[VMware ESXi]]. 
; Type-2 or hosted hypervisors
: These hypervisors run on a conventional operating system (OS) just as other computer programs do. A virtual machine monitor runs as a [[Computer process|process]] on the host, such as [[VirtualBox]]. Type-2 hypervisors abstract guest operating systems from the host operating system, effectively creating an isolated system that can be interacted with by the host. Examples of Type-2 hypervisor include [[VirtualBox]] and [[VMware Workstation]].

The distinction between these two types is not always clear. For instance, [[Kernel-based_Virtual_Machine|KVM]] and [[bhyve]] are [[kernel module]]s<ref>{{cite web |last=Dexter |first=Michael |title= Hands-on bhyve |url=http://callfortesting.org/bhyve/ |website=CallForTesting.org |access-date=2013-09-24}}</ref> that effectively convert the host operating system to a type-1 hypervisor.<ref name=IowaState>{{cite thesis |last=Graziano |first=Charles |title=A performance analysis of Xen and KVM hypervisors for hosting the Xen Worlds Project |type=MS thesis |publisher=Iowa State University |date=2011 |url=https://dr.lib.iastate.edu/handle/20.500.12876/26405 |doi=10.31274/etd-180810-2322 |hdl=20.500.12876/26405 |access-date=2022-10-16|doi-access=free }}</ref>