VirtualBox supports both Intel’s hardware virtualization VT-x and AMD’s AMD-V. VirtualBox attempts to run as much guest code natively (that is, directly on the host processor) as possible. This works well for user-mode code running in the guest’s ring 3 of the Intel ring architecture. However, the guest’s ring-0 code, which will usually contain many privileged instructions, will need to be intercepted. VirtualBox has a rather novel approach to fix this conflict: It tricks the guest operating system to actually execute its ring-0 code in ring 1, which is normally unused on the Intel architecture.
Virtualbox Hard disk Emulated
Hard disks are emulated in one of three disk image formats: a VirtualBox-specific container format called “Virtual Disk Image” (VDI) which are stored as files (with a .vdi suffix) on the host operating system ; VMware Virtual Machine Disk Format (VMDK); and Microsoft Virtual PC VHD format. This means that a VirtualBox virtual machine can be set up to use disks that were created in VMware or Microsoft Virtual PC as well as its own proprietary format. VirtualBox can also connect to iSCSI targets and to raw partitions on the host, using either as virtual hard disks.
Virtualbox CD/DVD Storage
Both ISO images and host-connected physical devices can be mounted as CD/DVD drives. For example the DVD image of a Linux distribution can be downloaded and used directly by VirtualBox.
VirtualBox Graphics Card
VirtualBox provides graphics support through a custom virtual graphics card which is VESA compatible. With the Guest Additions for Windows, Linux, Solaris or OS/2 guests comes a special video driver that allows for better performance and features such as dynamically adjusting the guest resolution when the VM window is resized.
VirtualBox Ethernet network adapter
VirtualBox virtualizes these Network Interface Cards: AMD PCnet PCI II (Am79C970A), AMD PCnet-Fast III (Am79C973), Intel Pro/1000 MT Desktop (82540EM), Intel Pro/1000 MT Server (82545EM), and Intel Pro/1000 T Server (82543GC).
Such a broad range of the emulated network cards allows running many operating systems without finding and installing drivers. By default, VirtualBox sets the network up with NAT through which user programs like Firefox or ssh can operate. For hosts other than Windows Vista, other options exist, such as virtual networks between guests. Up to eight network adapters can be attached simultaneously, but only four are configurable through the graphical interface.
For a sound card, VirtualBox virtualizes an Intel ICH AC’97 device or a SoundBlaster 16 card.
Virtualbox USB Controller
In the “full release” (not in the open-source edition), a USB controller is emulated (both USB 1.1 and USB 2.0) so that any USB devices attached to the host can be seen in the guest. If VirtualBox acts as an RDP server, it can also use USB devices on the remote RDP client as if they were connected to the host.
read more : http://en.wikipedia.org/wiki/VirtualBox