A hypervisor is a virtual machine monitor (VMM) that allows multiple operating systems to run simultaneously on one host computer.
The host computer shares its resources, such as CPU, memory, and storage, amongst the multiple guest virtual machines. Hypervisors prevent virtual machines from interfering with one another when running in parallel.
There are two types of hypervisors:
Type 1 hypervisors, or bare-metal hypervisor, are a type of hypervisor that run directly on the underlying hardware of a machine, where it interacts directly with the CPU, memory, and storage. A type 1 hypervisor essentially replaces the host operating system (OS).
Type 2 hypervisors are a type of hypervisor that do not run directly on the underlying hardware, but rather run as an application in an operating system (OS). Type 2 hypervisors are useful for individual PC users who want to run multiple OSs.