Virtualization

Type 1 Hypervisor

Virtualization allows us to break the one-to-one relationship of hardware to OS, allowing multiple OS's to run on a single physical server.

Each instance is called a VM (Virtual Machine).

A hypervisor is used to manage and allocate the hardware resources (CPU, RAM, etc) to each VM.

Another name for a hypervisor is VMM (Virtual Machine Monitor).

The type of hypervisor which runs directly on the top of the hardware is called a Type 1 hypervisor.

• Examples include VMware ESXi, Microsoft Hyper-V, etc.

Type 1 hypervisors are also called bare-metal hypervisors because they run directly on the hardware (metal).

• Another term is native hypervisor.

This is the type of hypervisor used in data center environments.

Type 2 Hypervisor

Type 2 hypervisors run as a program on an operating system like a regular computer program.

• Examples include VMware Workstation, Oracle VirtualBox, etc.

The OS running directly on the hardware is called the Host OS, and the OS running in a VM is called a Guest OS.

Another name for a Type 2 hypervisor is hosted hypervisor.

Although Type 2 hypervisors are rarely used in data center environments, they are common on personal-use devices (for example, if a Mac/Linux used needs to run an app that is only supported on Windows, or vice versa).