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<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE topic PUBLIC "-//OASIS//DTD DITA Topic//EN" "topic.dtd">
<topic xml:lang="en-us" id="guestadd-intro">
<title>Introduction to Guest Additions</title>
<body>
<p>As mentioned in <xref href="virtintro.dita#virtintro"/>, the Guest Additions are designed to be installed <i>inside</i> a virtual machine after the guest operating system has been installed. They consist of device drivers and system applications that optimize the guest operating system for better performance and usability. See <xref href="guest-os.dita"/> for details on what guest operating systems are fully supported with Guest Additions by <ph conkeyref="vbox-conkeyref-phrases/product-name"/>.</p>
<p>The <ph conkeyref="vbox-conkeyref-phrases/product-name"/> Guest Additions for all supported guest operating
systems are provided as a single CD-ROM image file which is called <filepath>VBoxGuestAdditions.iso</filepath>.
This image file is located in the installation directory of <ph conkeyref="vbox-conkeyref-phrases/product-name"/>.
To install the Guest Additions for a particular VM, you mount this ISO file in your VM as a virtual CD-ROM and
install from there. </p>
<p>The Guest Additions offer the following features: </p>
<ul>
<li>
<p><b outputclass="bold">Mouse pointer integration</b>. To
overcome the limitations for mouse support described in
<xref href="keyb_mouse_normal.dita#keyb_mouse_normal"/>, this feature provides
you with seamless mouse support. You will only have one mouse
pointer and pressing the Host key is no longer required to
<i>free</i> the mouse from being captured by the
guest OS. To make this work, a special mouse driver is
installed in the guest that communicates with the physical
mouse driver on your host and moves the guest mouse pointer
accordingly.
</p>
</li>
<li>
<p><b outputclass="bold">Shared folders.</b> These provide
an easy way to exchange files between the host and the guest.
Much like ordinary Windows network shares, you can tell
<ph conkeyref="vbox-conkeyref-phrases/product-name"/> to treat a certain host directory as a shared
folder, and <ph conkeyref="vbox-conkeyref-phrases/product-name"/> will make it available to the guest
operating system as a network share, irrespective of whether
the guest actually has a network. See
<xref href="sharedfolders.dita#sharedfolders"/>.
</p>
</li>
<li>
<p><b outputclass="bold">Better video support.</b> While the virtual graphics card which <ph
conkeyref="vbox-conkeyref-phrases/product-name"/> emulates for any guest operating
system provides all the basic features, the custom video drivers that are installed with
the Guest Additions provide you with extra high and nonstandard video modes, as well as
accelerated video performance. </p>
<p>In addition, with Windows, Linux, and Oracle Solaris guests, you can resize the virtual machine's window if
the Guest Additions are installed. The video resolution in the guest will be automatically adjusted, as if you
had manually entered an arbitrary resolution in the guest's <b outputclass="bold">Display</b> settings. See
<xref href="intro-resize-window.dita#intro-resize-window"/>. </p>
<p>If the Guest Additions are installed, 3D graphics for guest applications can be accelerated. See <xref href="guestadd-video.dita#guestadd-video"/>. </p>
</li>
<li>
<p><b outputclass="bold">Seamless windows.</b> With this
feature, the individual windows that are displayed on the
desktop of the virtual machine can be mapped on the host's
desktop, as if the underlying application was actually running
on the host. See <xref href="seamlesswindows.dita#seamlesswindows"/>.
</p>
</li>
<li>
<p><b outputclass="bold">Generic host/guest communication
channels.</b> The Guest Additions enable you to control
and monitor guest execution. The <i>guest
properties</i> provide a generic string-based mechanism
to exchange data bits between a guest and a host, some of
which have special meanings for controlling and monitoring the
guest. See <xref href="guestadd-guestprops.dita#guestadd-guestprops"/>.
</p>
<p>Additionally, applications can be started in a guest from the host. See <xref
href="guestadd-guestcontrol.dita#guestadd-guestcontrol"/>. </p>
</li>
<li>
<p><b outputclass="bold">Time synchronization.</b> With
the Guest Additions installed, <ph conkeyref="vbox-conkeyref-phrases/product-name"/> can ensure that
the guest's system time is better synchronized with that of
the host.
</p>
<p>For various reasons, the time in the guest might run at a slightly different rate than the time on the host.
The host could be receiving updates through NTP and its own time might not run linearly. A VM could also be
paused, which stops the flow of time in the guest for a shorter or longer period of time. When the wall clock
time between the guest and host only differs slightly, the time synchronization service attempts to gradually
and smoothly adjust the guest time in small increments to either catch up or lose time. When the difference is
too great, for example if a VM paused for hours or restored from saved state, the guest time is changed
immediately, without a gradual adjustment. </p>
<p>The Guest Additions will resynchronize the time regularly. See <xref href="changetimesync.dita">Tuning the
Guest Additions Time Synchronization Parameters</xref> for how to configure the parameters of the time
synchronization mechanism. </p>
</li>
<li>
<p><b outputclass="bold">Shared clipboard.</b> With the
Guest Additions installed, the clipboard of the guest
operating system can optionally be shared with your host
operating system. See <xref href="generalsettings.dita"/>.
</p>
</li>
<li>
<p><b outputclass="bold">Automated logins.</b> Also called
credentials passing. See <xref href="autologon.dita">Automated Guest Logins</xref>.
</p>
</li>
</ul>
<p>Each version of <ph conkeyref="vbox-conkeyref-phrases/product-name"/>, even minor releases, ship with their own
version of the Guest Additions. While the interfaces through which the <ph
conkeyref="vbox-conkeyref-phrases/product-name"/> core communicates with the Guest Additions are kept stable so
that Guest Additions already installed in a VM should continue to work when <ph
conkeyref="vbox-conkeyref-phrases/product-name"/> is upgraded on the host, for best results, it is recommended
to keep the Guest Additions at the same version. </p>
<p>The Windows and Linux Guest Additions therefore check automatically whether they have to be updated. If the host
is running a newer <ph conkeyref="vbox-conkeyref-phrases/product-name"/> version than the Guest Additions, a
notification with further instructions is displayed in the guest. </p>
<p>To disable this update check for the Guest Additions of a given virtual machine, set the value of its
<codeph>/VirtualBox/GuestAdd/CheckHostVersion</codeph> guest property to <codeph>0</codeph>. See <xref
href="guestadd-guestprops.dita#guestadd-guestprops"/>. </p>
</body>
</topic>
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