Many people have just one OS (Operating System) on their computers these days. Hardcore geekazoids like myself, may have more than one, but only one can be run at the same time. Switching from Windows XP Pro to Windows 2000, and then to Red Hat Linux 9.0 prove to be a bit of a pain. The pro to multiple operating systems in my opinion are the applications. My AutoCad release runs on Win 2000, Red Hat Linux has tons of free software, and Windows XP keeps me up to date with the rest of the world.
XenSource makes a product called the Xen hypervisor, which allows a computer to run more than one OS at a time. It supposedly is “a very thin layer of software that essentially presents to the operating system an idealized hardware abstraction”. I’d love to get my greasy little hands on this hypervisor! Expected due dates are set somewhere along the lines of 2010.