14 Known limitations This sections describes known problems with VirtualBox 4.0.4. 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. • For 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. • 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 typ- ing gpedit.msc, open the key Computer Configuration\Windows Settings\Security Set- tings\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 config- uration 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). 181