Hypervisor and virtualisation software splits one physical server into many virtual machines, each with its own operating system, memory and disks, as if each were a separate computer. The program that does the splitting is called a hypervisor, and the technique is called virtualisation. The best-known hypervisor in company data centres is VMware's. Others include KVM, which is built into Linux, and Microsoft's Hyper-V.
Why split a server? A physical server is powerful, and one app rarely uses all of it. Before virtualisation, companies ran one app on each server, and most servers sat idle most of the time. With a hypervisor, a company can run 20 or 30 virtual machines on one server. Each can run a different app, and even a different operating system. If one virtual machine crashes, the others keep running.
How does it work? The hypervisor runs directly on the server's hardware. It gives each virtual machine a share of the processors, memory, disks and network, and keeps the shares separate. A management program sits above many servers. It lets administrators create a virtual machine in minutes. It can move a virtual machine from one server to another while it is running, which is called live migration. And it can restart virtual machines automatically on another server if their server fails, which is called high availability.
Here is a typical case. An engineering company in Nashik runs its own data centre. It has 24 physical servers that host 450 virtual machines, for its ERP system, its design software, its email archive and its factory systems. ERP, or enterprise resource planning, is the software that runs a company's accounts, purchasing and stock. One night, a server's power supply fails. Within two minutes, the management software restarts the 18 virtual machines that were on it on other servers. The factory's night shift notices only a short pause.
In 2023, Broadcom bought VMware. Many customers then reported large price rises at renewal. They also reported a move from buying licences once to paying for a subscription every year, and bundles of products that they had not asked for. For the first time in about twenty years, many companies are choosing a hypervisor again. The engineering company in Nashik is one of them: its renewal quote is more than double its last one. It is testing three answers. One is hyperconverged infrastructure, which comes with its own hypervisor. Another is running virtual machines beside containers on a Kubernetes platform. A third is private cloud software such as OpenStack. Moving 450 virtual machines is a project of many months, so the decision is not quick.
Each virtual machine needs an operating system, often from an enterprise Linux subscription. Its disks usually live on shared enterprise storage systems. A virtual private server rented from a hosting company is also one of these virtual machines, on the hosting company's hypervisor.