We first covered the release of VirtualBox 4.0 back in January. Amongst other improvements and new features, 4.1 adds VM cloning and a nascent PCI passthrough feature.

The new cloning feature allows the user to easily make a copy of an existing VM including the hard disk image and all associated settings. It’s going to be particularly handy for people like me who create a lot of blank VMs with similar specs. This means that I can create a generic Linux 2.6 supporting VM with 1GM of RAM and a virtual HD of 8GB and then simply clone it when I need a new one. The speed of the cloning procedure varies according to the size of the HD file. For example, cloning a fresh VM with an unused dynamically scaling hard disk image takes almost no time, whereas cloning my Windows XP VM with a 4GB partition took a few minutes.

Virtual disk management has received a couple of useful enhancements. It is now possible to directly create and work with VMDK (VMware) and VHD (Microsoft Virtual PC) formats from the GUI. There is also a GUI interface for copying hard disk images. As with the cloning features, the new hard disk management features were already more-or-less possible from the command line and with a bit of extra trouble, but having them built into the GUI will be more convenient for those of us who prefer to work that way.

PCI Passthrough, a new Linux only feature looks intriguing, but according to the docs, it seems to be at early stage with limited hardware support. The feature allows guest operating systems to directly access PCI and PCI Express hardware, even in cases in which the hardware is not supported by the host. This could offer benefits in two main areas: Firstly, it offers the potential to greatly improve the performance of hardware such as network adaptors when accessed from within a VM. Secondly, it would allow Linux to use hardware (albeit via a VM) that either has no, or only limited, Linux driver support. For the moment, only specific combinations of motherboard chipset and add on card are supported. Something tells me that this is a feature worth watching out for in the future. See the appropriate section of the manual for more info.

Note that version 4.1 increases the memory limit to 1TB for 64 bit guests. So, it looks like developers are already thinking about support for KDE5. A new GUI for setting the CPU cap makes it possible to limit the amount of processor time that a VM can gobble.

You can now tame hungry VMs in terms of CPU usage.

Networking is another area in which there have been a few improvements. UDP tunneling is a special mode for efficient networking between VMs running on different physical machines. Note that there was already a special mode to speed up communication between VMs running on the same host. There is also a new generic virtual network adaptor that offers an open plugin standard. How useful this is will depend on what uses developers of other projects dream up for it.

In addition to the new features, 4.1 includes dozens of bug fixes. As one might expect from a point release, 4.1 doesn’t present any major changes. However, the additions that have been made to the first update of the 4.x series offer some handy new features at least one glimpse of an intriguing new possibility in the form of the PCI passthrough.

The VirtualBox website.