view docs/src/user/glossary.tex @ 7727:d7bcc7bbf981

Fix region0 virtual accesses
Signed-off by: Dan Magenheimer <dan.magenheimer@hp.com>
author djm@kirby.fc.hp.com
date Fri Nov 11 12:51:08 2005 -0600 (2005-11-11)
parents 06d84bf87159
children bc7567741a4c
line source
1 \chapter{Glossary of Terms}
3 \begin{description}
5 \item[Atropos] One of the CPU schedulers provided by Xen. Atropos
6 provides domains with absolute shares of the CPU, with timeliness
7 guarantees and a mechanism for sharing out `slack time'.
9 \item[BVT] The BVT scheduler is used to give proportional fair shares
10 of the CPU to domains.
12 \item[Exokernel] A minimal piece of privileged code, similar to a {\bf
13 microkernel} but providing a more `hardware-like' interface to the
14 tasks it manages. This is similar to a paravirtualising VMM like
15 {\bf Xen} but was designed as a new operating system structure,
16 rather than specifically to run multiple conventional OSs.
18 \item[Domain] A domain is the execution context that contains a
19 running {\bf virtual machine}. The relationship between virtual
20 machines and domains on Xen is similar to that between programs and
21 processes in an operating system: a virtual machine is a persistent
22 entity that resides on disk (somewhat like a program). When it is
23 loaded for execution, it runs in a domain. Each domain has a {\bf
24 domain ID}.
26 \item[Domain 0] The first domain to be started on a Xen machine.
27 Domain 0 is responsible for managing the system.
29 \item[Domain ID] A unique identifier for a {\bf domain}, analogous to
30 a process ID in an operating system.
32 \item[Full virtualisation] An approach to virtualisation which
33 requires no modifications to the hosted operating system, providing
34 the illusion of a complete system of real hardware devices.
36 \item[Hypervisor] An alternative term for {\bf VMM}, used because it
37 means `beyond supervisor', since it is responsible for managing
38 multiple `supervisor' kernels.
40 \item[Live migration] A technique for moving a running virtual machine
41 to another physical host, without stopping it or the services
42 running on it.
44 \item[Microkernel] A small base of code running at the highest
45 hardware privilege level. A microkernel is responsible for sharing
46 CPU and memory (and sometimes other devices) between less privileged
47 tasks running on the system. This is similar to a VMM, particularly
48 a {\bf paravirtualising} VMM but typically addressing a different
49 problem space and providing different kind of interface.
51 \item[NetBSD/Xen] A port of NetBSD to the Xen architecture.
53 \item[Paravirtualisation] An approach to virtualisation which requires
54 modifications to the operating system in order to run in a virtual
55 machine. Xen uses paravirtualisation but preserves binary
56 compatibility for user space applications.
58 \item[Shadow pagetables] A technique for hiding the layout of machine
59 memory from a virtual machine's operating system. Used in some {\bf
60 VMMs} to provide the illusion of contiguous physical memory, in
61 Xen this is used during {\bf live migration}.
63 \item[Virtual Machine] The environment in which a hosted operating
64 system runs, providing the abstraction of a dedicated machine. A
65 virtual machine may be identical to the underlying hardware (as in
66 {\bf full virtualisation}, or it may differ, as in {\bf
67 paravirtualisation}).
69 \item[VMM] Virtual Machine Monitor - the software that allows multiple
70 virtual machines to be multiplexed on a single physical machine.
72 \item[Xen] Xen is a paravirtualising virtual machine monitor,
73 developed primarily by the Systems Research Group at the University
74 of Cambridge Computer Laboratory.
76 \item[XenLinux] Official name for the port of the Linux kernel that
77 runs on Xen.
79 \end{description}