Why have just one operating system
I'm currently running three different operating systems on my desktop PC. There's my habitual Kubuntu Linux, a version of Android (more common on phones), and Windows. They're running simultaneously and I can select any one with a mouse click.
This magic comes about by the use of "virtualisation" - which simply refers to the creation of a virtual (rather than an actual) version of something. With the right software and a reasonably powerful PC, you can build virtual "compartments" inside your computer that look and act like a whole separate machine. That allows you, for example, to run Linux and Mac on Windows, try out a new web server or run an old operating system such as DOS or OS/2, all without disturbing your current system - or having to reboot. "Guest" systems can communicate with the underlying (or "host" operating system) via shared folders, networking or the clipboard, and you can install and run as many VMs (virtual machines) as you like, with disk space and memory the only real limitation. More amazingly, the extremely clever software is open source. And that means it's free.
VirtualBox, from virtualbox.org, is available for Linux, Mac and Windows and requires 40-90MB of disk space depending on your operating system. There's also an Extension Pack containing some extra goodies and an extremely detailed manual on the site.
Installation is perfectly straightforward, as is setting up a new VM. In most cases it's simply a matter of clicking OK to the default recommendations. Once that's done, click Start and your virtual machine boots in a window on your actual machine. You can boot from an installation CD or DVD - just as in a normal installation - or from a disk image. (Linux distributions typically come as images ready to write to a physical disk and VirtualBox can boot straight from those images.) Virtualisation allows you to try out a whole host of other operating systems without having to reboot or run them from CD, and because they're software- based you can halt and save them at any point and restart exactly where you left off - giving a "boot time" of just a few seconds.
Because operating systems are stored as virtual disk images they can be distributed as such. Sites like virtualboxes.org allow you to download and try out a huge variety of free operating systems without going through the process of actually installing them.
- Geoff Palmer is a computer consultant, freelance technical writer and novelist.