This article describes briefly what Virtual Machines are, why they are useful, and compares some VM software for Mac OS X:
As web developers, it is often our responsibility to ensure that the websites we build are accessible by users of any common web browser and operating system. Since some browsers are only available on a limited selection of
OSes, or behave differently on different OSes, it is impossible to be able to test a website on all browsers with one operating system; In order to test websites frequently, we need to have ready access to a variety of operating systems. Many folk use a secondary machine to run secondary OSes on, or dual-boot their primary computer. However having a mostly-redundant computer sitting by can be expensive, and dual-booting is time-consuming to switch OSes and does not allow you to access tools in your primary OS while testing in the secondary OS.
