Oracle has announced a major update to its open-source, cross-platform virtualization software. VirtualBox 4.1, which allows users to run different operating systems in virtual environments through a window, boasts a number of major new features, including support for VM cloning and an experimental WDDM graphics driver providing Windows Aero support in Windows guests. There’s also a networking mode (UDP tunnel) that’s designed to allow VMs running on different hosts to connect easily and transparently.

In addition to these new features, VirtualBox 4.1 includes some user-interface improvements, including the ability to keep the aspect ratio scaled in Windows and Mac OS X hosts when manually resizing the guest window. In addition to this it features numerous bug fixes and other minor tweaks.

The new VM cloning feature allows users to make both full and linked clones. Full clones can be made through both the main user interface (right-click the VM machine and choose Clone) and VBoxManage; linked clones require the latter.

Those running Windows 7 and Vista guests will be interested to see that VirtualBox has implemented an experimental WDDM graphics driver that supports both Windows Aero and Direct3D (the latter’s guest drivers can now be installed outside of Safe Mode). Windows Aero support has finally been delivered around two years after it was first requested.

Other notable new features include a “Generic Driver” network attachment mode offering an open plug-in architecture, plus VirtualBox now raises the memory limit for 64-bit hosts all the way to 1TB. User interface improvements include new and enhanced wizards for copying and creating virtual disks. Version 4.1 also includes a large number of other minor tweaks and bug fixes.

VirtualBox 4.1 is a free, open-source download for Windows, Mac OS X and Linux. A separate download, the VirtualBox Extension Pack, which adds support for USB2.0, remote control of guests and PXE boot, is also available, under a “free for personal use” license. This has also been updated to version 4.1.