For many years now, one of the most popular pieces of proprietary software under GNU/Linux has been VMWare. Its powerful ability to run other operating systems unmodified inside of a running Linux kernel has generally been unmatched by free software, leading many to pay the (rather substantial) price to run VMWare for that pesky Windows application that they, for one reason or another, cannot abandon or replace. Over the years, there have been many valiant efforts to replace this useful tool with truly Free Software, but only in the last year (and with some corporate help) has this goal been reached. 

For many years the most promising Free virtual machine for x86 was Xen, a 'hypervisor' which runs on the bare hardware, running a Linux instance in a special, privleged virtual machine to manage the virtualization system. In addition to being a rather heavyweight approach, it generally requires modifications to the operating systems running in the virtual machines,  making it useful for servers (since the modified OS can 'cooperate' with the hypervisor to make the virtual machine run smoothly), but generally unsuitable for the desktop user faced with an annoying legacy program. Xen's modifications to the Linux kernel have also had a long, hard road to being merged into the standard kernel distribution, and the available Free management tools remain somewhat primitive, as Xen's developers earn money selling proprietary management tools for Xen.

However, in the past year, two virtual machines have been released to the community under the GNU GPL: KVM and VirtualBox. KVM was first, in fall 2006, and depends on the hardware virtualization support added to new x86 processors by Intel and AMD; this makes KVM very simple and has sped its inclusion in the base Linux kernel. It is VirtualBox, though, that is the true free VMWare replacement, as its user tools are much better developed and simpler to use than KVM's. 

VirtualBox was released under the GPL in January 2007 by a German software company called innotek. This source release included both the core virtual machine and the corresponding user-space management tools, though a few components were held back as a 'value-added' offering. Like VMWare and unlike KVM, VirtualBox is a purely software-based virtualization environment, using emulation and code modification to work around operations in the virtualized OS that would otherwise reveal the difference between running in the virtual machine and running directly on the real machine. 

VirtualBox, like VMWare, is nearly as fast as the base processor it is virtualizing. When it is used to run Windows or Linux, additional speed and versatility can be gained by installing the 'Guest Additions' within the VM, which are drivers that cooperate with VirtualBox to speed up I/O and allow for features such as seamless mouse movement between the VirtualBox window and the rest of the desktop. With these installed, the virtual machine will appear on your desktop like any other window, allowing convenient access to a different OS environment directly from the Linux desktop. VirtualBox supports suspend and resume for virtual machines (termed 'Snapshots'), making the virtual environment even more accessible.

VirtualBox does have a few flaws when compared with its more mature competition, some of which are purposeful deficiencies in the Open-Source Edition. Support for virtualized USB devices is available, but reserved for the proprietary free-for-personal-use-only version. Similarly, the proprietary version allows direct remote access to the virtual machine's screen through Microsoft's ubiquitous Remote Desktop Protocol. Additionally, the Guest Additions video driver does not support full screen DirectX applications under Windows, preventing VirtualBox from being used as a supplement to WINE for playing old Windows games. 

VirtualBox is a powerful, free VMWare replacement that is already suitable for many of the tasks previously requiring expensive VMWare licenses. It is available for both Windows and Linux, with Mac OS X support in beta, and is known to run both Windows and Linux stably. Other PC operating systems, including FreeBSD, Solaris and OS/2, are being worked on and may also be stable under VirtualBox. Development is progressing rapidly, with five minor revisions in the ten months since the original source release; the latest version of VirtualBox is available from or in Debian unstable. 

This writeup is copyright 2007 D.G. Roberge and is released under the Creative Commons Attribution-NonCommercial-ShareAlike licence. Details can be found at .

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