Virtual Machines and Hypervisors

Virtualization lets one physical server pretend to be many separate computers. Each pretend computer is a virtual machine (VM) with its own operating system, applications, virtual CPU, memory, and disk. The VMs share the real hardware underneath but stay isolated from each other.

This is the foundation of modern data centers and the cloud. Instead of one application per physical box, a single powerful server can host dozens of VMs, cutting cost, power use, and floor space dramatically.

A hypervisor (also called a Virtual Machine Monitor) is the software layer that creates and runs VMs. It carves up the physical CPU, RAM, and storage and hands slices to each VM, keeping them isolated so one crash cannot take down its neighbors.

The hypervisor schedules access to real hardware, just like an operating system schedules apps. To each guest OS, it looks like the VM owns a complete physical machine.