Virtualization
Running multiple isolated virtual machines on one physical server by abstracting the hardware — the foundation of cloud computing.
Virtualization abstracts physical hardware so that multiple isolated virtual machines, each with its own OS, run on one physical server — coordinated by a hypervisor. It is the foundation of cloud computing: it turns one big machine into many rentable slices and decouples workloads from specific hardware.
Worked example: a cloud provider runs dozens of customers’ VMs on one physical host; each VM believes it has its own machine, fully isolated from the others, and can be moved to another host without the guest OS noticing. Gotcha: full virtualization carries the weight of a whole guest OS per VM (slow to boot, GBs of RAM), which is exactly why containers — which virtualize at the OS level and share the host kernel — emerged as a lighter alternative for packaging applications; VMs give stronger isolation, containers give density and speed.