1.. SPDX-License-Identifier: CC-BY-4.0
2
3Glossary
4========
5
6.. Terms should appear in alphabetical order
7
8.. glossary::
9
10   control domain
11     A :term:`domain`, commonly dom0, with the permission and responsibility
12     to create and manage other domains on the system.
13
14   domain
15     A domain is Xen's unit of resource ownership, and generally has at the
16     minimum some RAM and virtual CPUs.
17
18     The terms :term:`domain` and :term:`guest` are commonly used
19     interchangeably, but they mean subtly different things.
20
21     A guest is a single, end user, virtual machine.
22
23     In some cases, e.g. during live migration, one guest will be comprised of
24     two domains for a period of time, while it is in transit.
25
26   domid
27     The numeric identifier of a running :term:`domain`.  It is unique to a
28     single instance of Xen, used as the identifier in various APIs, and is
29     typically allocated sequentially from 0.
30
31   guest
32     The term 'guest' has two different meanings, depending on context, and
33     should not be confused with :term:`domain`.
34
35     When discussing a Xen system as a whole, a 'guest' refer to a virtual
36     machine which is the "useful output" of running the system in the first
37     place (e.g. an end-user VM).  Virtual machines providing system services,
38     (e.g. the control and/or hardware domains), are not considered guests in
39     this context.
40
41     In the code, "guest context" and "guest state" is considered in terms of
42     the CPU architecture, and contrasted against hypervisor context/state.
43     In this case, it refers to all code running lower privilege privilege
44     level the hypervisor.  As such, it covers all domains, including ones
45     providing system services.
46
47   hardware domain
48     A :term:`domain`, commonly dom0, which shares responsibility with Xen
49     about the system as a whole.
50
51     By default it gets all devices, including all disks and network cards, so
52     is responsible for multiplexing guest I/O.
53