Why choose between Windows 7 and Snow Leopard when you can have both? A Mac with virtualization software is a great platform for running Mac OS X, Windows, Linux, or other Intel-based operating systems, all at the same time. There's also Mac OS X's native Boot Camp, but it only supports Windows and doesn't give you access to Mac OS X without rebooting.
The latest versions of the Mac virtualization products from Parallels, VMware, and Sun offer significant improvements over previous versions, and all are worth the upgrade. They're faster with better 3-D graphics, are better integrated with Mac OS X, and in two cases, are optimized for running all the features of Windows 7.
[ Also on InfoWorld.com: Virtualization isn't the only way to run Windows apps on your Mac. See "CrossOver: Windows apps without Windows." ]
Overall, Parallels Desktop 5 for Mac is the top virtualizer for Mac OS X. VMware Fusion 3 is a close second, with Sun's VirtualBox 3.1 running a distant third. VirtualBox has a few unique features and is free, but doesn't support many Mac OS X features. Parallels Desktop 5 and VMware Fusion 3 also automate the installation of guest operating systems and support multiple monitors. Furthermore, these new versions add support for Windows 7 Aero features, such as Aero Peek and Aero Glass. VirtualBox doesn't do any of these.
Parallels Desktop 5 provides the best overall performance. Not that VMware Fusion 3 is slow, but it can stumble with graphics-heavy tasks and uses more of the Mac's processor, leaving less CPU bandwidth for Mac applications.
On interface and Mac OS X integration issues, the merits of Parallels and VMware are more subjective. Both do a good job of hiding the Windows desktop and integrating Windows applications in the Dock, Expose, and Spaces. Both are far more advanced than VirtualBox's Seamless mode.
If you want to run Mac OS X Server in a virtual machine, however, VMware Fusion 3 is the clear choice, providing the most trouble-free and solid experience. Parallels can have trouble installing or importing Apple's server in a virtual machine, and VirtualBox just doesn't support it.
Where Parallels beats VMware
Parallels Desktop 5 and VMware Fusion 3 both have new support for DirectX 9.0c Shader Model 3, OpenGL 2.1, and the Windows WDDM driver. These graphic hardware acceleration technologies enable support for Aero in Windows 7 and Vista, as well as 3-D gaming. Parallels Desktop 5 goes one step further and supports OpenGL 2.1 in Linux guest operating systems, enabling the Compiz interface to run in a virtual machine.
This story, "Windows on the Mac: Parallels 5 vs. Fusion 3 vs. VirtualBox 3.1" was originally published by InfoWorld .