VirtualBox

History

VirtualBox was initially offered by Innotek GmbH from Weinstadt, Germany under a proprietary software license, making one version of the product available at no cost for personal or evaluation use, subject to the VirtualBox Personal Use and Evaluation License (PUEL). In January 2007, based on counsel by LiSoG, Innotek GmbH released VirtualBox Open Source Edition (OSE) as free and open-source software, subject to the requirements of the GNU General Public License (GPL), version 2.

Innotek GmbH also contributed to the development of OS/2 and Linux support in virtualization and OS/2 ports of products from Connectix which were later acquired by Microsoft. Specifically, Innotek developed the “additions” code in both Microsoft Virtual PC and Microsoft Virtual Server, which enables various host-guest OS interactions like shared clipboards or dynamic viewport resizing.

Sun Microsystems acquired Innotek in February 2008.

Oracle Corporation acquired Sun in January 2010 and re-branded the product as "Oracle VM VirtualBox".

Licensing

The core package is, since version 4 in December 2010, free software under GNU General Public License version 2 (GPLv2). The separate "VirtualBox Oracle VM VirtualBox extension pack" providing support for USB 2.0 devices, Remote Desktop Protocol (RDP) and Preboot Execution Environment (PXE) is under a proprietary license, called Personal Use and Evaluation License (PUEL), which permits use of the software for personal use, educational use, or evaluation, free of charge. Oracle defines personal use as any situation in which one person installs the software, and only that individual, and their friends and family, use the software. Oracle does not care if that use is for commercial or non-commercial purposes.

Prior to version 4, there were two different packages of the VirtualBox software. The full package was offered free under the PUEL, with licenses for other commercial deployment purchasable from Oracle. A second package called the VirtualBox Open Source Edition (OSE) was released under GPLv2. This removed the same proprietary components not available under GPLv2.

Building the BIOS for VirtualBox since version 4.2 requires the use of the Open Watcom compiler, for which the Sybase Open Watcom Public License is approved as "Open Source" by the Open Source Initiative but not as "free" by the Free Software Foundation or under the Debian Free Software Guidelines.

Although VirtualBox has experimental support for Mac OS X guests, the end user license agreement of Mac OS X does not permit the operating system to run on non-Apple hardware, and this is enforced within the operating system by calls to the Apple System Management Controller (SMC) in all Apple machines, which verifies the authenticity of the hardware.

Emulated environment

Users of VirtualBox can load multiple guest OSs under a single host operating-system (host OS). Each guest can be started, paused and stopped independently within its own virtual machine (VM). The user can independently configure each VM and run it under a choice of software-based virtualization or hardware assisted virtualization if the underlying host hardware supports this. The host OS and guest OSs and applications can communicate with each other through a number of mechanisms including a common clipboard and a virtualized network facility. Guest VMs can also directly communicate with each other if configured to do so.

Software-based virtualization

In the absence of hardware-assisted virtualization, VirtualBox adopts a standard software-based virtualization approach. This mode supports 32-bit guest OSs which run in rings 0 and 3 of the Intel ring architecture.

The system reconfigures the guest OS code, which would normally run in ring 0, to execute in ring 1 on the host hardware. Because this code contains many privileged instructions which cannot run natively in ring 1, VirtualBox employs a Code Scanning and Analysis Manager (CSAM) to scan the ring 0 code recursively before its first execution to identify problematic instructions and then calls the Patch Manager (PATM) to perform in-situ patching. This replaces the instruction with a jump to a VM-safe equivalent compiled code fragment in hypervisor memory.

The guest user-mode code, running in ring 3, generally runs directly on the host hardware in ring 3.

In both cases, VirtualBox uses CSAM and PATM to inspect and patch the offending instructions whenever a fault occurs. VirtualBox also contains a dynamic recompiler, based on QEMU to recompile any real mode or protected mode code entirely (e.g. BIOS code, a DOS guest, or any operating system startup).

Using these techniques, VirtualBox can achieve a performance comparable to that of VMware.

Hardware-assisted virtualization

VirtualBox supports both Intel's VT-x and AMD's AMD-V hardware-virtualization. Making use of these facilities, VirtualBox can run each guest VM in its own separate address-space; the guest OS ring 0 code runs on the host at ring 0 in VMX non-root mode rather than in ring 1.

VirtualBox supports some guests (including 64-bit guests, SMP guests and certain proprietary OSs) only on hosts with hardware-assisted virtualization.

Device virtualization

The system emulates hard disks in one of three disk image formats:

1. VDI: This format is the VirtualBox-specific VirtualBox Disk Image and stores data in files bearing a ".vdi" filename extension.
2. VMDK: This open format is used by VMWare products such as VMWare Workstation and VMWare Player. It stores data in one or more files bearing ".vmdk" filename extensions. A single virtual hard disk may span several files.
3. VHD: This format is used by Windows Virtual PC, and is the native virtual disk format of the Microsoft Windows operating system, starting with Windows 7 and Windows Server 2008 R2. Data in this format are stored in a single file bearing the ".vhd" filename extension.

A VirtualBox virtual machine can, therefore, use disks previously created in VMware or Microsoft Virtual PC, as well as its own native format. VirtualBox can also connect to iSCSI targets and to raw partitions on the host, using either as virtual hard disks. VirtualBox emulates IDE (PIIX4 and ICH6 controllers), SCSI, SATA (ICH8M controller) and SAS controllers to which hard drives can be attached.

VirtualBox has supported Open Virtualization Format (OVF) since version 2.2.0 (April 2009).

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.

By default VirtualBox provides graphics support through a custom virtual graphics-card that is VESA compatible. The Guest Additions for Windows, Linux, Solaris, OpenSolaris, or OS/2 guests include a special video-driver that increases video performance and includes additional features, such as automatically adjusting the guest resolution when resizing the VM window or desktop composition via virtualized WDDM drivers .

For an 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)

Intel Pro/1000 T Server (82543GC)

Paravirtualized network adapter (virtio-net)

The emulated network cards allow most guest OSs to run without the need to find and install drivers for networking hardware as they are shipped as part of the guest OS. A special paravirtualized network adapter is also available, which improves network performance by eliminating the need to match a specific hardware interface, but requires special driver support in the guest. (Many distributions of Linux ship with this driver included.) By default, VirtualBox uses NAT through which Internet software for end-users such as Firefox or ssh can operate. Bridged networking via a host network adapter or virtual networks between guests can also be configured. Up to 36 network adapters can be attached simultaneously, but only four are configurable through the graphical interface.

For a sound card, VirtualBox virtualizes Intel HD Audio, Intel ICH AC'97 and SoundBlaster 16 devices.

A USB 1.1 controller is emulated so that any USB devices attached to the host can be seen in the guest. The proprietary extension pack adds a USB 2.0 or USB 3.0 controllers and, 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, although only if the client supports this VirtualBox-specific extension (Oracle provides clients for Solaris, Linux and Sun Ray thin clients that can do this, and have promised support for other platforms in future versions).

Feature set

64-bit guests (hardware virtualization support is required)

Snapshots

Seamless mode - the ability to run virtualized applications side by side with normal desktop applications

Shared clipboard

Shared folders

Special drivers and utilities to facilitate switching between systems

Command line interaction (in addition to the GUI)

Public API (Java, Python, SOAP, XPCOM) to control VM configuration and execution

Nested paging for AMD-V and Intel VT (only for processors supporting SLAT and with SLAT enabled)

Limited support for 3D graphics acceleration (including OpenGL up to (but not including) 3.0 and Direct3D 9.0c via Wine's Direct3D to OpenGL translation)

SMP support (up to 32 virtual CPUs per virtual machine), since version 3.0

Teleportation (aka Live Migration)

2D video output acceleration (not to be mistaken with video decoding acceleration), since version 3.1

EFI has been supported since version 3.1

Storage emulation features

NCQ support for SATA, SCSI and SAS raw disks and partitions

SATA disks hotplugging

Pass-through mode for solid-state drives

Pass-through mode for CD/DVD/BD disks - allows to play audio CDs, burn optical disks, play encrypted DVD disks

Can disable host OS I/O cache

Allows to limit IO bandwidth

PATA, SATA, SCSI, SAS, iSCSI, floppy disk controllers

VM disk image encryption using AES128/AES256

Storage support

Raw hard disk access – allows physical hard disk partitions on the host system to appear in the guest system

VMware Virtual Machine Disk (VMDK) format support – allows VirtualBox to exchange disk images with VMware

Microsoft VHD support

QEMU qed and qcow disks

HDD format disks (only version 2; version 3 and 4 are not supported) used by Parallels virtualization products

Since version 3.2

Mac OS X Server guest support – experimental

Memory ballooning (not available on Solaris hosts)

RAM deduplication (Page Fusion) for Windows guests on 64-bit hosts

CPU hot-plugging for Linux (hot-add and hot-remove) and certain Windows guests (hot-add only)

Deleting snapshots while the VM is running

Multi-monitor guest setups in the GUI, for Windows guests

LSI Logic SAS controller emulation

Remote Desktop Protocol (RDP) video acceleration via a non-free extension

Run and control guest applications from the host – for automated software deployments

Since version 4.0

The PUEL/OSE separation was given up in favor of an open source base product and a closed source extension pack that can be installed on top of the base product. As part of this change, additional components of VirtualBox were made open source (installers, documentation, device drivers)

Intel HD audio codec emulation

Intel ICH9 chipset emulation

A new VM storage scheme where all VM data is stored in one single folder to improve VM portability

Several UI enhancements including a new look with VM preview and scale mode

On 32-bit hosts, VMs can each use more than 1.5 GB of RAM

In addition to OVF, the single file OVA format is supported

CPU use and I/O bandwidth can be limited per VM

Support for Apple DMG images (DVD)

Multi-monitor guest setups for Linux/Solaris guests (previously Windows only)

Resizing of disk image formats from Oracle, VDI (VirtualBox disk image), and Microsoft, VHD (Virtual PC hard disk)

Since version 4.1

Windows Aero support (experimental)

Virtual machine cloning

Since version 4.2

Virtual machine groups - allows you to manage a group of virtual machines as a single unit (power them on or off, snapshot them, etc.)

Some VM settings can be altered during a VM execution

Support up to 36 NICs in case of the ICH9 chipset

Support for limiting network IO bandwidth

Can automatically run VMs on a host system startup (except on Windows host)

Since version 4.3

VM video capturing support

Host touch devices support (GUI passes host touch-events to guest)/USB virtualization of such devices

Since version 5.0

Paravirtualization support for Windows and Linux guests to improve time-keeping accuracy and performance

USB3 controller based on Intel's hardware implementation. It's supported by any Windows version starting from Windows 7, any Linux kernel starting from 2.6.31 and Mac OS X starting from version 10.7.4.

Bidirectional drag and drop support for Windows, Linux and Solaris guests

VM disk image encryption via a non-free extension

VM output scaling and HiDPI displays support

Hotplugging of SATA disks using GUI

USB traffic capturing

VMs can be disconnected from a GUI session and run in background

AVX, AVX-2, AES-NI, SSE 4.1/4.2 instructions (if supported by the host CPU)

Limitations

VirtualBox has a very low transfer rate from and to USB2 devices.

Even though VirtualBox is an open source product some of its features are supplied only in a binary form under a commercial license (see The extension pack below).

USB3 devices pass through is not supported by older guest OSes like Windows Vista and Windows XP due to the lack of drivers.

Guest Additions for MacOS are unavailable at this time.

Guest Additions for Windows 9x (Windows 95, 98 and ME) are unavailable at this time. This results in poor performance due to the lack of graphics acceleration with the default 16-bit color mode (external third-party software is available to enable support for 32-bit color mode, resulting in better performance).

EFI support for guest systems is limited (incomplete EFI is supported - full support for EFI or support for UEFI is unavailable).

Only older versions of DirectX and OpenGL passthrough are supported (the feature can be enabled using the 3D Acceleration option for each VM individually).

Video RAM is limited to 128 MiB (256 MiB with 2D Video Acceleration enabled) due to technical difficulties (merely changing the GUI to allow the user to allocate more video RAM to a VM or manually editing the configuration file of a VM wouldn't work and will result in a fatal error).

VirtualBox Extension Pack

Some features require the installation of the closed-source "VirtualBox Extension Pack":

Support for a virtual USB 2.0/3.0 controller (EHCI/xHCI)

VirtualBox RDP: support for proprietary remote connection protocol developed by Microsoft and Citrix.

PXE boot for Intel cards

VM disk image encryption

Host OS support

Since version 5, VirtualBox has stated that they are dropping support for Windows XP host, thus leaving its users with Windows XP hosts vulnerable to flaws of earlier releases. VirtualBox can also be run under GNU/Linux, OS X, Sun Solaris and FreeBSD.