Real virtuality

Though you can never have too much speed, modern PCs are more than equal to the task of running basic productivity programs and Web browsers in a Linux-based graphical user interface. If your PC has untapped RAM, disk space and CPU horsepower, here's a great way to put that horsepower to work: install a virtual operating system (OS).

Virtualisation lets your main OS run copies of other OSes the same way you run programs, either in a window or full-screen. The host OS (a Linux distribution or Microsoft Windows) and the virtualisation software assign resources - network connections, optical drives, memory and the like - to the virtualised operating system, which behaves as if it controls the entire PC.

Who should use virtualisation software? If you're contemplating dual- or triple-booting operating systems on your PC, or you want to see how a new version of your current distribution behaves before upgrading, you'll want to consider it. Virtualisation software allows you to install and run a new OS without having to repartition your drive or reboot your main operating system. Virtualisation also lets you do risky things, like browse the Web using an unpatched version of Windows XP, without endangering the host system. Should someone hack into your virtualised OS, the damage remains within the confines of the virtual container - to undo the damage, all you have to do is delete the virtual drive.

Until recently, virtualisation was an expensive proposition. But recent events have given Linux and Windows users a choice of several powerful, free, virtualisation tools.

The art of Xen

XenSource's Xen 3.0 (www.xensource.com) is a free, open-source virtualisation server that works with any Linux distribution and comes partially preinstalled in Novell's SuSE Linux 10.1 and OpenSuSE 10.1, and Red Hat's Enterprise Linux 5 and Fedora Core 5 distributions, click here for a screenshot.

Because Xen is small and runs as part of the Linux kernel, it has a reputation for good performance: given enough memory, virtualised OSes should run nearly as fast as the host OS. However, Xen has a few drawbacks. For example, both host and guest operating systems must be recompiled to work with Xen, which limits the operating systems and distributions you can use. (See the Xen Wiki for a complete list.) Notably, you cannot currently run Windows XP virtually under Xen.

Most importantly, be prepared to become an expert at installing and configuring Xen; familiarising yourself with the user manual is a good way to start. VMWare: not choosy

If you want to run Windows XP - or any other OS compatible with your computer's processor - in a virtual machine under Linux, bypass Xen and go to VMWare's free VMWare Virtual Server (www.vmware.com), click here to view a screenshot. The benefits are mostly the same as those of Xen 3.0 - you can try out new operating systems and run risky programs under XP with no fear that malware will take over your PC - but the performance lag is more noticeable than with Xen.

Once you've installed VMWare Virtual Server (a multistep process that's well-documented in its user manual), you can install the operating system of your choice within a virtual machine, or skip the installation and simply download and plug in one of dozens of "virtual applications" (preinstalled and preconfigured VMWare virtual machine image files) from the company's Virtual Appliances directory. Ranging in size from a few megabytes to a gigabyte, VMWare's virtual applications include full-blown Linux distributions, databases, software firewalls, wikis, PBXs, proxy servers and security suites.

Microsoft's offering

Finally, you might want to try virtualising the other way around. Not to be out-freebied, Microsoft recently released a free virtualisation program of its own, Microsoft Virtual Server 2005 R2 (click here to view a screenshot), which runs Linux and other operating systems under Windows XP Professional Edition or Windows Server 2003. (Sorry, it won't work with Windows XP Home Edition.) The security benefits are different, but someone out there will undoubtedly want to run Linux under Windows, if only to dip a toe in the open-source waters before jumping ship.