A host operating system can run more than one hypervisor at a time, and each hypervisor in turn can run more than one guest, but ultimately all converge on the host operating system and its kernel. Type 2, also known as hosted, runs a primary host operating system on the hardware, and hypervisors then run on top of, or in close conjunction with, that to deliver the same range of services to the guest operating systems. Examples of this type include VMware ESX Server and Microsoft Hyper-V. The hypervisor is then responsible for managing those virtual machines (VMs), giving them virtual CPUs (vCPUs), virtual memory, and other hardware resources. Type 1, also known as native or bare metal, runs a hypervisor directly on its hardware, and the guest operating systems run on that hypervisor. The name is derived from it being the supervisor of supervisors.Īlmost fifty years ago, a distinction was drawn between what were then seen as the two types of virtualisation. This provides a layer of abstraction somewhere between the guest operating system and hardware of the host, roughly equivalent to the kernel in an operating system which isn’t virtualised. This article explains some of the background, in the context of virtualisation on Apple silicon Macs.Ĭentral to virtualisation is software known as a hypervisor, which makes it all possible. Since then virtualisation has developed and flourished, and Intel, ARM and others have added hardware support. When desktop PCs and Macs first came out, most operating systems and hardware went hand-in-hand, and there was little interest in trying to virtualise one operating system on another that’s perhaps just as well, as processors and memory management weren’t able to assist. Running multiple operating systems on the same computer is a very old trick which, as some have pointed out, goes back to the early days of IBM mainframe computer systems.

Apple virtualization framework