# Known limitations

## Experimental Features

Some VirtualBox features are labeled as experimental. Such features are provided on an "as-is" basis and are not formally supported. However, feedback and suggestions about such features are welcome. A comprehensive list of experimental features follows:

- WDDM Direct3D video driver for Windows guests
- Hardware 3D acceleration support for Windows, Linux, and Solaris guests
- Hardware 2D video playback acceleration support for Windows guests
- PCI pass-through (Linux hosts only)
- Mac OS X guests (Mac hosts only)
- ICH9 chipset emulation
- EFI firmware
- Host CD/DVD drive pass-through
- Support of iSCSI via internal networking
- Synthetic CPU reporting

## Known Issues

The following section describes known problems with VirtualBox $VBOX_VERSION_STRING. Unless marked otherwise, these issues are planned to be fixed in later releases.

- The following Guest SMP (multiprocessor) limitations exist:

  - Poor performance with 32-bit guests on AMD CPUs. This affects mainly Windows and Solaris guests, but possibly also some Linux kernel revisions. Partially solved in 3.0.6 for 32 bits Windows NT, 2000, XP and 2003 guests. Requires 3.0.6 or higher Guest Additions to be installed.

  - Poor performance with 32-bit guests on certain Intel CPU models that do not include virtual APIC hardware optimization support. This affects mainly Windows and Solaris guests, but possibly also some Linux kernel revisions. Partially solved in 3.0.12 for 32 bits Windows NT, 2000, XP and 2003 guests. Requires 3.0.12 or higher Guest Additions to be installed.

- 64-bit guests on some 32-bit host systems with VT-x can cause instabilities to your system. If you experience this, do not attempt to execute 64-bit guests. Refer to the VirtualBox user forum for additional information.

- NX (no execute, data execution prevention) only works for guests running on 64-bit hosts or guests running on 32-bit hosts with PAE enabled and requires that hardware virtualization be enabled.

- For basic Direct3D support in Windows guests to work, the Guest Additions must be installed in Windows "safe mode". Press F8 when the Windows guest is booting and select "Safe mode", then install the Guest Additions. Otherwise Windows' file protection mechanism will interfere with the replacement DLLs installed by VirtualBox and keep restoring the original Windows system DLLs.

  This does not apply to the experimental WDDM Direct3D video driver available for Vista and Windows 7 guests shipped with VirtualBox 4.1.

- Guest control. On Windows guests, a process lauched via the guest control execute support will not be able to display a graphical user interface unless the user account under which it is running is currently logged in and has a desktop session.

  Also, to use accounts without or with an empty password, the guest's group policy must be changed. To do so, open the group policy editor on the command line by typing `gpedit.msc`, open the key Computer Configuration\Windows Settings\Security Settings\Local Policies\Security Options and change the value of Accounts: Limit local account use of blank passwords to console logon only to Disabled.

- Compacting virtual disk images is limited to VDI files. The `VBoxManage modifyhd --compact` command is currently only implemented for VDI files. At the moment the only way to optimize the size of a virtual disk images in other formats (VMDK, VHD) is to clone the image and then use the cloned image in the VM configuration.

- OVF import/export:

  - OVF localization (multiple languages in one OVF file) is not yet supported.

  - Some OVF sections like StartupSection, DeploymentOptionSection and InstallSection are ignored.

  - OVF environment documents, including their property sections and appliance configuration with ISO images, are not yet supported.

  - Remote files via HTTP or other mechanisms are not yet supported.

- Neither scale mode nor seamless mode work correctly with guests using OpenGL 3D features (such as with compiz-enabled window managers).

- The RDP server in the VirtualBox extension pack supports only audio streams in format 22.05kHz stereo 16 bit. If the RDP client requests any other audio format there will be no audio.

- Preserving the aspect ratio in scale mode works only on Windows hosts and on Mac OS X hosts.

- On Mac OS X hosts, the following features are not yet implemented:

  - Numlock emulation

  - CPU frequency metric

  - Memory ballooning

- Mac OS X guests:

  - Mac OS X guests can only run on a certain host hardware. For details about license and host hardware limitations, please see intro-macosxguests and check the Apple software license conditions.

  - VirtualBox does not provide Guest Additions for Mac OS X at this time.

  - The graphics resolution currently defaults to 1024x768 as Mac OS X falls back to the built-in EFI display support. See efividmode for more information on how to change EFI video modes.

  - Mac OS X guests only work with one CPU assigned to the VM. Support for SMP will be provided in a future release.

  - Depending on your system and version of Mac OS X, you might experience guest hangs after some time. This can be fixed by turning off energy saving (set timeout to "Never") in the system preferences.

  - By default, the VirtualBox EFI enables debug output of the Mac OS X kernel to help you diagnose boot problems. Note that there is a lot of output and not all errors are fatal (they would also show on your physical Mac). You can turn off these messages by issuing this command:

        VBoxManage setextradata "VM name" "VBoxInternal2/EfiBootArgs" "  "

    To revert to the previous behavior, use:

        VBoxManage setextradata "VM name" "VBoxInternal2/EfiBootArgs" ""

  - It is currently not possible to start a Mac OS X guest in safe mode by specifying "-x" option in "VBoxInternal2/EfiBootArgs" extradata.

- Solaris hosts:

  - There is no support for USB devices connected to Solaris 10 hosts.

  - USB support on Solaris hosts requires Solaris 11 version snv_124 or higher. Webcams and other isochronous devices are known to have poor performance.

  - No ACPI information (battery status, power source) is reported to the guest.

  - No support for using wireless adapters with bridged networking.

  - Crossbow-based bridged networking on Solaris 11 hosts does not work directly with aggregate links. However, you can manually create a VNIC (using `dladm`) over the aggregate link and use that with a VM. This technical limitation will be addressed in a future Solaris 11 release.

- Guest Additions of version 4.1, 4.1.2 and 4.1.4 for Windows Thus VirtualBox WDDM Video driver may be installed and kept in guest system if Guest additions uninstallation is performed. This is caused by a bug in Guest Additions uninstaller.

  This does not apply to Guest Additions update, i.e. installing a one version of Guest Additions on top of another works correctly.

  To solve this problem, one should uninstall the VirtualBox WDDM Video driver manually. To do that open Device Manager, and check whether the Display Adapter is named "VirtualBox Graphics Adapter ..". If no - there is nothing to be done. If yes - right-click the VirtualBox Graphics Adapter in Device Manager, select "Uninstall", check "Delete the driver software for this device" and click "OK". Once uninstallation is done - in Device Manager go to menu "Action" and select "Scan for hardware changes" to make the propper (Windows default) driver be picked up for the Graphics adapter.

- Neither virtio nor Intel PRO/1000 drivers for Windows XP guests support segmentation offloading. Therefore Windows XP guests have slower transmission rates comparing to other guest types. Refer to MS Knowledge base article 842264 for additional information.

- Guest Additions for OS/2. Shared folders are not yet supported with OS/2 guests. In addition, seamless windows and automatic guest resizing will probably never be implemented due to inherent limitations of the OS/2 graphics system.