Hypervisor
Also known as: virtual machine monitor, VMM, virtualization platform
A hypervisor is software that creates and runs virtual machines, dividing one physical computer's processor, memory, and storage among several isolated virtual computers. 'Type 1' hypervisors, such as VMware ESXi, Microsoft Hyper-V, and KVM, run directly on server hardware, while 'Type 2' hypervisors, such as VirtualBox and Parallels, run as apps on a desktop.
Hypervisors underpin cloud computing. While virtualization saves money and space, a hypervisor failure or compromise can affect every virtual machine on that server.
Hypervisor, explained at three levels
At home
A hypervisor is like a landlord who divides a big house into separate apartments. Each tenant, a virtual machine, has their own space but shares the building.
At work
Hypervisors let businesses run many servers on fewer physical machines, saving hardware, power, and space.
At home
Free tools like VirtualBox or Hyper-V on Windows Pro let you try another operating system safely inside a window on your computer.
At work
Type 1 hypervisors run on bare metal for performance and security. Features include live migration, snapshots, high availability, and resource pools. Licensing models vary widely.
At home
Running a virtual machine needs plenty of RAM, since it borrows from your computer. In my opinion, 16 GB is the practical minimum for comfortable home virtualization.
At work
Secure hypervisor management interfaces on isolated networks with MFA, patch hosts promptly, and back up virtual machines outside the hypervisor. Ransomware groups increasingly target ESXi hosts directly to encrypt many servers at once.
Real-world examples
At home
Carlos wanted to try Linux without changing his PC. He installed VirtualBox and ran Ubuntu in a window alongside Windows.
At work
Fatima manages IT for a Halifax manufacturing company. After VMware's licence costs rose sharply, she migrated the company's 20 virtual servers to Hyper-V.
How it compares
| feature | Type 1 hypervisor | Type 2 hypervisor |
|---|---|---|
| Runs on | Directly on hardware | Inside an operating system |
| Examples | ESXi, Hyper-V, KVM | VirtualBox, Parallels, VMware Workstation |
| Performance | Higher | Lower |
| Typical use | Servers, data centres | Desktops, testing |
Type 1 runs servers. Type 2 runs VMs on your desktop.
For analysts
When virtualization licences come up for renewal, I'd run a structured options analysis. The VMware changes showed how quickly a stable cost can become a budget crisis.
History & origin
IBM developed virtualization for mainframes in the 1960s with systems such as CP-40 and CP-67, and Gerald Popek and Robert Goldberg formalized requirements for virtualization in 1974. VMware, founded in 1998, brought virtualization to ordinary PCs and later servers, transforming data centres. Open-source Xen in 2003, Intel and AMD hardware virtualization features in 2005 and 2006, KVM in the Linux kernel in 2007, and Microsoft Hyper-V in 2008 followed. Amazon Web Services and other clouds built on hypervisors. After Broadcom bought VMware in November 2023, licensing changes and price increases pushed many organizations to consider alternatives such as Proxmox, Nutanix, and Hyper-V. In my view, the hypervisor is the invisible foundation of the cloud.