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Virtualization Fundamentals

Virtualization lets one physical computer host multiple software-defined computers called virtual machines. A hypervisor divides processor time, memory, storage, and network access while each virtual machine runs its own operating system.

itVirtualization, containers, and orchestration

Virtualization Fundamentals

Virtualization presents software-defined computing hardware to an operating system. That operating system runs inside a virtual machine, or VM, instead of controlling a physical computer directly. A hypervisor sits at the control boundary. It schedules virtual processors, maps guest memory, connects virtual devices to host resources, and isolates one VM from another.

This arrangement separates a workload's operating environment from a particular server. Several VMs can share one host, while each VM keeps its own kernel, processes, accounts, filesystems, and network configuration. A VM can also move between compatible hosts when its storage and virtual hardware remain accessible.

The host, hypervisor, and guest

A virtualization stack has three main roles:

  • The host supplies physical processors, memory, storage, network interfaces, and accelerators.
  • The hypervisor controls access to those resources and exposes virtual hardware.
  • The guest is the operating system and applications inside a VM.

Hypervisors are often described as type 1 or type 2. A type 1 hypervisor runs as the platform's control layer and hosts VMs above it. A type 2 hypervisor runs through a conventional host operating system. The distinction helps with orientation, but products do not always fit a clean diagram. KVM, for example, makes the Linux kernel part of the hypervisor while QEMU supplies a machine model and device emulation.

Hardware-assisted virtualization lets selected guest instructions run on the physical processor while preserving hypervisor control. When a guest performs an operation that requires mediation, execution exits to the hypervisor. The hypervisor handles the event and then resumes the guest. Full CPU emulation takes a different path: software translates instructions, which permits a guest architecture to differ from the host but adds more overhead.

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