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 user-domain (domU) is granted virtual resources and can be started, stopped and restarted independently of other domains and of the host server itself. As a result, a configuration change applied to the virtual resources of a domU does not affect any other domains; and a failure of the domU does not impact any other domains. 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 allocated to the domain by the hypervisor running on the Oracle VM Server. Additional facilities to allow communication between a guest and the Oracle VM infrastructure can be installed on the guest operating system, including the Oracle VM Guest Additions. Note that you can install the Oracle VM Guest Additions on Oracle Linux guests only. Find out more about the Oracle VM Guest Additions in Installing and Using the Oracle VM Guest Additions in the Oracle VM Administrator's Guide.

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