Editing Hypervisor (section)

==x86 systems==
{{main|x86 virtualization}}{{More citations needed|section|date=April 2023}}
[[X86 virtualization]] was introduced in the 1990s, with its emulation being included in [[Bochs]].<ref>{{Cite web |title=Introduction to Bochs |url=https://bochs.sourceforge.io/doc/docbook/user/introduction.html |access-date=2023-04-17 |website=bochs.sourceforge.io}}</ref> Intel and AMD released their first x86 processors with hardware virtualisation in 2005 with [[Intel VT-x]] (code-named Vanderpool) and [[AMD-V]] (code-named Pacifica).

An alternative approach requires modifying the guest operating system to make a [[system call]] to the underlying hypervisor, rather than executing machine I/O instructions that the hypervisor simulates. This is called [[paravirtualization]] in [[Xen]], a "hypercall" in [[Parallels Workstation]], and a "DIAGNOSE code" in IBM [[VM (operating system)|VM]]. Some microkernels, such as [[Mach microkernel|Mach]] and [[L4 microkernel family|L4]], are flexible enough to allow paravirtualization of guest operating systems.