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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="technical-components">
<title><ph conkeyref="vbox-conkeyref-phrases/product-name"/> Executables and Components</title>
<body>
<p>
<ph conkeyref="vbox-conkeyref-phrases/product-name"/> was designed to be modular and flexible. When the
<ph conkeyref="vbox-conkeyref-phrases/product-name"/> graphical user interface (GUI) is opened and a VM
is started, at least the following three processes are running:
</p>
<ul>
<li>
<p><userinput>VBoxSVC</userinput>, the <ph conkeyref="vbox-conkeyref-phrases/product-name"/> service process
which always runs in the background. This process is started
automatically by the first <ph conkeyref="vbox-conkeyref-phrases/product-name"/> client process and
exits a short time after the last client exits. The first
<ph conkeyref="vbox-conkeyref-phrases/product-name"/> service can be <ph conkeyref="vbox-conkeyref-phrases/vbox-mgr"/>,
<userinput>VBoxManage</userinput>,
<userinput>VBoxHeadless</userinput>, the web service amongst
others. The service is responsible for bookkeeping,
maintaining the state of all VMs, and for providing
communication between <ph conkeyref="vbox-conkeyref-phrases/product-name"/> components. This
communication is implemented using COM/XPCOM.
</p>
<note>
<p>
When we refer to <i>clients</i> here, we mean
the local clients of a particular <userinput>VBoxSVC</userinput>
server process, not clients in a network. <ph conkeyref="vbox-conkeyref-phrases/product-name"/>
employs its own client/server design to allow its processes
to cooperate, but all these processes run under the same
user account on the host operating system, and this is
totally transparent to the user.
</p>
</note>
</li>
<li>
<p>
The GUI process, <userinput>VirtualBoxVM</userinput>, a client
application based on the cross-platform Qt library. When
started without the <codeph>--startvm</codeph> option, this
application acts as <ph conkeyref="vbox-conkeyref-phrases/vbox-mgr"/>, displaying the VMs and their
settings. It then communicates settings and state changes to
<userinput>VBoxSVC</userinput> and also reflects changes effected
through other means, such as the <userinput>VBoxManage</userinput>
command.
</p>
</li>
<li>
<p>
If the <userinput>VirtualBoxVM</userinput> client application is
started with the <codeph>--startvm</codeph> argument, it loads
the VMM library which includes the actual hypervisor and then
runs a virtual machine and provides the input and output for
the guest.
</p>
</li>
</ul>
<p> Any <ph conkeyref="vbox-conkeyref-phrases/product-name"/> front end, or client, will
communicate with the service process and can both control and reflect the current state. For
example, either the VM selector or the VM window or VBoxManage can be used to pause the
running VM, and other components will always reflect the changed state. </p>
<p>
The <ph conkeyref="vbox-conkeyref-phrases/product-name"/> GUI application, called <ph conkeyref="vbox-conkeyref-phrases/vbox-mgr"/>, is only one
of several available front ends, or clients. The complete list
shipped with <ph conkeyref="vbox-conkeyref-phrases/product-name"/> is as follows:
</p>
<ul>
<li>
<p><userinput>VirtualBoxVM</userinput>: The Qt front end implementing
<ph conkeyref="vbox-conkeyref-phrases/vbox-mgr"/> and running VMs.
</p>
</li>
<li>
<p><userinput>VBoxManage</userinput>: A less user-friendly but more
powerful alternative. See <xref href="vboxmanage.dita">VBoxManage</xref>.
</p>
</li>
<li>
<p><userinput>VBoxHeadless</userinput>: A VM front end which does not
directly provide any video output and keyboard or mouse input,
but enables redirection through the VirtualBox Remote Desktop
Extension. See <xref href="vboxheadless.dita"/>.
</p>
</li>
<li>
<p><userinput>vboxwebsrv</userinput>: The <ph conkeyref="vbox-conkeyref-phrases/product-name"/> web service
process which enables control of an <ph conkeyref="vbox-conkeyref-phrases/product-name"/> host
remotely. This is described in detail in the <ph conkeyref="vbox-conkeyref-phrases/product-name"/>
Software Development Kit (SDK) reference. See
<xref href="VirtualBoxAPI.dita"/>.
</p>
</li>
<li>
<p>
The <ph conkeyref="vbox-conkeyref-phrases/product-name"/> Python shell: A Python alternative to
<userinput>VBoxManage</userinput>. This is also described in the
SDK reference.
</p>
</li>
</ul>
<p>
Internally, <ph conkeyref="vbox-conkeyref-phrases/product-name"/> consists of many more or less separate
components. You may encounter these when analyzing <ph conkeyref="vbox-conkeyref-phrases/product-name"/>
internal error messages or log files. These include the following:
</p>
<ul>
<li>
<p>
IPRT: A portable runtime library which abstracts file access,
threading, and string manipulation. Whenever <ph conkeyref="vbox-conkeyref-phrases/product-name"/>
accesses host operating features, it does so through this
library for cross-platform portability.
</p>
</li>
<li>
<p>
VMM (Virtual Machine Monitor): The heart of the hypervisor.
</p>
</li>
<li>
<p>
EM (Execution Manager): Controls execution of guest code.
</p>
</li>
<li>
<p>
TRPM (Trap Manager): Intercepts and processes guest traps and
exceptions.
</p>
</li>
<li>
<p>
HM (Hardware Acceleration Manager): Provides support for VT-x
and AMD-V.
</p>
</li>
<li>
<p>
GIM (Guest Interface Manager): Provides support for various
paravirtualization interfaces to the guest.
</p>
</li>
<li>
<p>
PDM (Pluggable Device Manager): An abstract interface between
the VMM and emulated devices which separates device
implementations from VMM internals and makes it easy to add
new emulated devices. Through PDM, third-party developers can
add new virtual devices to <ph conkeyref="vbox-conkeyref-phrases/product-name"/> without having to
change <ph conkeyref="vbox-conkeyref-phrases/product-name"/> itself.
</p>
</li>
<li>
<p>
PGM (Page Manager): A component that controls guest paging.
</p>
</li>
<li>
<p>
TM (Time Manager): Handles timers and all aspects of time
inside guests.
</p>
</li>
<li>
<p>
CFGM (Configuration Manager): Provides a tree structure which
holds configuration settings for the VM and all emulated
devices.
</p>
</li>
<li>
<p>
SSM (Saved State Manager): Saves and loads VM state.
</p>
</li>
<li>
<p>
VUSB (Virtual USB): A USB layer which separates emulated USB
controllers from the controllers on the host and from USB
devices. This component also enables remote USB.
</p>
</li>
<li>
<p>
DBGF (Debug Facility): A built-in VM debugger.
</p>
</li>
<li>
<p>
<ph conkeyref="vbox-conkeyref-phrases/product-name"/> emulates a number of devices to provide the
hardware environment that various guests need. Most of these
are standard devices found in many PC compatible machines and
widely supported by guest operating systems. For network and
storage devices in particular, there are several options for
the emulated devices to access the underlying hardware. These
devices are managed by PDM.
</p>
</li>
<li>
<p>
Guest Additions for various guest operating systems. This is
code that is installed from within a virtual machine. See
<xref href="guestadditions.dita">Guest Additions</xref>.
</p>
</li>
<li>
<p>
The "Main" component is special. It ties all the above bits
together and is the only public API that <ph conkeyref="vbox-conkeyref-phrases/product-name"/>
provides. All the client processes listed above use only this
API and never access the hypervisor components directly. As a
result, third-party applications that use the <ph conkeyref="vbox-conkeyref-phrases/product-name"/>
Main API can rely on the fact that it is always well-tested
and that all capabilities of <ph conkeyref="vbox-conkeyref-phrases/product-name"/> are fully exposed.
It is this API that is described in the <ph conkeyref="vbox-conkeyref-phrases/product-name"/> SDK.
See <xref href="VirtualBoxAPI.dita#VirtualBoxAPI"/>.
</p>
</li>
</ul>
</body>
</topic>
|
