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+[% topdir = "../.." -%]
+[% PROCESS globals -%]
+[% WRAPPER page
+   title = "Names and terms used in the virt tools documentation"
+   h1 = "Names and terms used in the virt tools documentation"
+   section = "learning"
+   local_stylesheet = 1
+%]
+
+[% WRAPPER h2 h2="Hosts, guests, virtual machines, hypervisors" anchor="names" %]
+
+<p>
+The virt tools and
+<a href="[% topdir %]/about/#projects">project documentation</a>
+uses the terms
+<strong>guest</strong>,
+<strong>virtual machine</strong>,
+<strong>VM</strong> and
+<strong>domain</strong> interchangably to refer to a virtual machine.
+The term <q>domain</q> comes from Xen.
+</p>
+
+<p>
+When we say <strong>host</strong> we mean the ordinary physical machine
+and the operating system which contains the guests.
+</p>
+
+<p>
+The term <strong>hypervisor</strong> has several different meanings:
+</p>
+
+<ul>
+<li> It can refer to the virtualization technology being employed.
+For example you can discuss the pros and cons of VMWare vs
+KVM as a <strong>hypervisor technology</strong>. </li>
+<li> For some virtualization systems (notably Xen) it can
+mean a separate component (the <strong>Xen hypervisor</strong>)
+which provides virtualization.  In Xen, unlike other systems,
+the host runs on top of the hypervisor and behaves more like a
+specialized guest. </li>
+<li> For KVM, you can refer to <q>Linux as the hypervisor</q>,
+meaning that the ordinary Linux host kernel has extra hypervisor
+capabilities provided by the KVM module. </li>
+</ul>
+
+<p>
+Xen (only) uses the special terms <strong>Dom0</strong> (a.k.a.
+<strong>Domain-0</strong>) and <strong>DomU</strong> as synonyms
+for host and guest respectively.
+</p>
+
+[% END %]
+
+[% WRAPPER h2 h2="Full virtualization and paravirtualization" anchor="fvpv" %]
+
+<p class="vtmarginnote">
+Examples of full virtualization technologies:
+Bochs, QEMU, KVM, VMWare, Xen-FV, MAME.
+</p>
+
+<p>
+<strong>Full virtualization</strong> (or <strong>fullvirt</strong>,
+<strong>FV</strong>) is what you use to run an unmodified operating
+system as a virtual machine.  The operating system <q>thinks</q> it is
+running on a PC, and (from the point of view of the guest) it sees
+usual hardware like a keyboard, disk drive, monitor and so on.  These
+of course are not real, but are emulated by the hypervisor technology
+underneath.
+</p>
+
+<p>
+Full virtualization is usually a bit slower, because of all the
+emulation, but it has the big advantage that you can run unmodified
+operating systems like Windows.
+</p>
+
+<p>
+<strong>Paravirtualization</strong>
+(or <strong>paravirt</strong>, <strong>PV</strong>) is where you
+modify the guest operating system so that it knows it is running in a
+virtual machine and it cooperates with the host.  This is done to gain
+extra performance by avoiding unnecessary emulation.
+</p>
+
+<p>
+There are essentially two methods currently in use for
+paravirtualization.  The <strong>Xen paravirt</strong> approach makes
+deep changes to the Linux kernel so that cooperation is achieved at
+many levels.  The advantage of Xen paravirt is
+that <a href="#hardware">hardware support</a> is not required, but the
+disadvantage is it is only possible for some Linux guests.
+</p>
+
+<p class="vtmarginnote">
+Examples of FV with PV drivers technologies:
+KVM Virtio, VMWare Tools, VirtualBox Additions, Xen-PV drivers.
+</p>
+
+<p>
+The more common approach these days is <strong>device driver
+paravirtualization</strong> where only the device drivers of the
+operating system are replaced.  This is sometimes called
+<strong>fullvirt with PV drivers</strong>.  This gains almost all the
+performance benefits of paravirtualization, it works with Windows
+guests, and it can be implemented incrementally by starting with a
+fullvirt guest and adding PV drivers as required.  The downside is
+that you need hardware support.  The most commonly paravirtualized
+devices are: the hard disk (often called the <q>block device</q>), the
+network device, the console, and the clock.
+</p>
+
+<p>
+<strong>Virtio</strong> is an emerging standard for
+paravirtualized drivers, and is particularly used for
+QEMU and KVM guests.  Virtio PV drivers are available
+for many different operating systems.
+</p>
+
+[% END %]
+
+[% WRAPPER h2 h2="Hardware support for virtualization" anchor="hardware" %]
+
+<p>
+Nowadays most computer processors contain extra support to accelerate
+virtualization (see <a href="../check-hardware-virt/">this tutorial to
+check if yours has support and to find out more about the different
+types</a>).
+</p>
+
+<p>
+Support in hardware is often called <strong>hardware
+virtualization</strong> (or <strong>hardware virt</strong>),
+abbreviated to <strong>HVM</strong>.
+</p>
+
+[% END %]
+
+[% WRAPPER h2 h2="Lifecycle" anchor="lifecycle" %]
+
+<p>
+Virtual machines can be started and stopped, and you may see this
+being referred to as the <strong>lifecycle</strong>
+or <strong>lifecycle management</strong>.  This is entirely equivalent
+to switching a real machine on and off.
+</p>
+
+<p>
+As well as just being started and stopped (and unlike real machines),
+virtual machines can be <strong>paused</strong>,
+<strong>snapshotted</strong> and <strong>cloned</strong>.
+</p>
+
+<p>
+Taking a snapshot usually means to save the state of the
+virtual machine at a moment in time, either so it can be
+backed up consistently, or so that you can try some experimental
+operation and roll back to the snapshot if that fails.
+</p>
+
+<p>
+Cloning is somewhat similar to snapshotting, but the two
+clones are allowed to run independently of each other
+(and cannot be combined again), so that whereas before you
+had one virtual machine, now you have two.
+</p>
+
+<p>
+Another aspect of lifecycle management is <strong>saving</strong>
+and <strong>restoring</strong> virtual machines.
+</p>
+
+[% END %]
+
+[% WRAPPER h2 h2="Disks and storage" anchor="storage" %]
+
+<p>
+The hard drive of a virtual machine is usually emulated ie.  it's not
+a physical, separate hard drive, but a file or logical volume on the
+host.  This host file (or however it is stored) is called
+the <strong>disk image</strong>.
+</p>
+
+<p>
+Disk images are allocated in <strong>volumes</strong>
+out of <strong>storage pools</strong>.
+</p>
+
+[% END %]
+
+[% WRAPPER h2 h2="Migration" anchor="migration" %]
+
+<p>
+<strong>Migration</strong> means moving a virtual machine from
+one host to another.  Usually this means <strong>live migration</strong>
+where the running VM is moved without interruption.
+</p>
+
+<p>
+Don't confuse migration and conversion (see next section).
+</p>
+
+[% END %]
+
+[% WRAPPER h2 h2="P2V, V2V and V2P" anchor="p2v" %]
+
+<p>
+The terms <strong>P2V</strong>,
+<strong>V2V</strong>, and <strong>V2P</strong> refer to different
+sorts of <strong>conversions</strong>:
+</p>
+
+<table>
+<tr>
+<th> P2V </th>
+<td> Physical to virtual: Converting a physical machine to a
+virtual machine.  This is often done so you can continue to
+use the applications on the physical machine, but with newer
+hardware underneath. </td>
+</tr>
+<tr>
+<th> V2V </th>
+<td> Virtual to virtual: Converting a virtual machine
+from one hypervisor technology to another, for example
+converting a VMWare virtual machine to run on KVM to
+save money. </td>
+</tr>
+<tr>
+<th> V2P </th>
+<td> Virtual to physical: This is the reverse of P2V, taking
+a virtual machine and restoring it onto a physical machine. </td>
+</tr>
+</table>
+
+[% END %]
+
+[% END -%]