Hypervisor

A hypervisor, also known as a virtual machine monitor (VMM) or virtualizer, is a type of computer <a href="/facts/Software/RP79lVSW">software</a>, <a href="/facts/Firmware/62UVKIUK">firmware</a> or <a href="/facts/Computer_hardware/8jSjsCNv">hardware</a> that creates and runs <a href="/facts/Virtual_machine/BLevU3sx">virtual machines</a>. A computer on which a hypervisor runs one or more virtual machines is called a host machine, and each virtual machine is called a guest machine. The hypervisor presents the guest operating systems with a <a href="/facts/Platform_virtualization/6e2Bhhz2">virtual operating platform</a> and manages the execution of the guest operating systems. Unlike an <a href="/facts/Emulator/FMHE8qDj">emulator</a>, the guest executes most instructions on the native hardware. Multiple instances of a variety of operating systems may share the virtualized hardware resources: for example, <a href="/facts/Linux/9FvCKSTq">Linux</a>, <a href="/facts/Microsoft_Windows/bwhAhuSL">Windows</a>, and <a href="/facts/MacOS/Y93vVpTm">macOS</a> instances can all run on a single physical <a href="/facts/X86/Kypq5fgu">x86</a> machine. This contrasts with <a href="/facts/Operating-system-level_virtualization/gkLoCrgN">operating-system–level virtualization</a>, where all instances (usually called containers) must share a single kernel, though the guest operating systems can differ in <a href="/facts/User_space/0yIzMY8t">user space</a>, such as different <a href="/facts/Linux_distribution/0vVl4N4f">Linux distributions</a> with the same kernel.
The term hypervisor is a variant of supervisor, a traditional term for the <a href="/facts/Kernel_(operating_system)/uEj4U3Rz">kernel</a> of an <a href="/facts/Operating_system/8XTuvMh2">operating system</a>: the hypervisor is the supervisor of the supervisors, with hyper- used as a stronger variant of super-. The term dates to circa 1970; IBM coined it for software that ran <a href="/facts/OS%2f360/nQbdNbx6">OS/360</a> and the 7090 emulator concurrently on the <a href="/facts/IBM_System%2f360_Model_65/Clz78CuQ">360/65</a> and later used it for the DIAG handler of CP-67. In the earlier <a href="/facts/CP%2fCMS/zzHA1Rzz">CP/CMS</a> (1967) system, the term Control Program was used instead.
Some literature, especially in <a href="/facts/Microkernel/wsaWtYCU">microkernel</a> contexts, makes a distinction between hypervisor and virtual machine monitor (VMM). There, both components form the overall virtualization stack of a certain system. Hypervisor refers to <a href="/facts/User_space_and_kernel_space/0yIzMY8t">kernel-space</a> functionality and VMM to <a href="/facts/User_space_and_kernel_space/0yIzMY8t">user-space</a> functionality. Specifically in these contexts, a hypervisor is a microkernel implementing virtualization infrastructure that must run in kernel-space for technical reasons, such as <a href="/facts/X86_virtualization/utQwmdY3">Intel VMX</a>. Microkernels implementing virtualization mechanisms are also referred to as microhypervisor. Applying this terminology to <a href="/facts/Linux/9FvCKSTq">Linux</a>, <a href="/facts/Kernel-based_Virtual_Machine/d6eSuTuK">KVM</a> is a hypervisor and <a href="/facts/QEMU/s6utqULJ">QEMU</a> or Cloud Hypervisor are VMMs utilizing KVM as hypervisor.

Hypervisor open-in-new

Hypervisor