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10 Technical background
or the VM window or VBoxManage can be used to pause the running VM, and other
components will always reflect the changed state.
The VirtualBox GUI application is only one of several available front-ends (clients).
The complete list shipped with VirtualBox is:
1. VirtualBox, the Qt GUI front end mentioned earlier.
2. VBoxManage, a less user-friendly but more powerful alternative to the GUI described in chapter 8, VBoxManage, page 114.
3. VBoxSDL, a simple graphical front end based on the SDL library; see chapter 9.2,
VBoxSDL, the simplified VM displayer, page 153.
4. VBoxHeadless, a VM front end which does not directly provide any video output
and keyboard/mouse input, but allows redirection via VRDP; see chapter 7.1.2,
VBoxHeadless, the VRDP-only server, page 106.
5. vboxwebsrv, the VirtualBox web service process which allows for controlling a
VirtualBox host remotely. This is described in detail in the VirtualBox Software
Development Kit (SDK) reference; please see chapter 11, VirtualBox programming interfaces, page 184 for details.
6. The VirtualBox Python shell, a Python alternative to VBoxManage. This is also
described in the SDK reference.
Internally, VirtualBox consists of many more or less separate components. You may
encounter these when analyzing VirtualBox internal error messages or log files. These
include:
• IPRT, a portable runtime library which abstracts file access, threading, string
manipulation, etc. Whenever VirtualBox accesses host operating features, it does
so through this library for cross-platform portability.
• VMM (Virtual Machine Monitor), the heart of the hypervisor.
• EM (Execution Manager), controls execution of guest code.
• REM (Recompiled Execution Monitor), provides software emulation of CPU instructions.
• TRPM (Trap Manager), intercepts and processes guest traps and exceptions.
• HWACCM (Hardware Acceleration Manager), provides support for VT-x and
AMD-V.
• 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 VirtualBox without having to change
VirtualBox itself.
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