The terms domain, guest and virtual machine are often used interchangeably, but they have subtle differences. A domain is a configurable set of resources, including memory, virtual CPUs, network devices and disk devices, in which virtual machines run. A domain is granted virtual resources and can be started, stopped and restarted independently of other domains and of the host server itself. A guest is a virtualized operating system running within a domain.

Oracle VM is designed for the purpose of running multiple guests in a virtualized environment, while providing the tools to easily manage, configure and maintain the virtual machines that guests run on. These virtual machines run on Oracle VM Servers that are grouped together into server pools. This makes it possible to easily migrate the virtual machine where a guest is running to another similar server without interrupting service. In a clustered server pool where a guest is configured to support High Availability, the guest can automatically be restarted on an alternate server when the server where a guest is running is under particular load or where a server becomes unavailable at any point.

Oracle VM guests consume resources that are made available to the domain in which they are running by the Oracle VM Server hypervisor. Additional facilities to allow communication between a guest and the Oracle VM infrastructure can be installed on the guest operating system. These facilities are usually provided in the form of the Oracle VM Guest Additions.

Oracle VM guests and the virtual machines where they run are discussed in more detail in Chapter 7, Understanding Virtual Machines.