When copying an image, some configuration settings need to be changed before the virtual machine will run. Parallels provides basic image management tools, built into the GUI, including options for cloning an image. Fusion lets you just copy the directory, and then when you start up the image asks if this is a copy and fixes it up. While I've never had a cloned image fail in Parallels, copied images occasionally haven't worked in Fusion.

A more sophisticated operation is the compression of images. Compression removes unnecessary space in the disk image, so it takes up less room on the host disk. Parallel's compressor is built into the GUI. Fusion ships with a command-line tool. You probably won't see much benefit when compressing newly created images, but virtual machines that have been in use for some time are good candidates for compression.

Perhaps the most taxing of all management tasks is converting a physical machine to a virtual image: a P2V conversion. Parallels and Fusion offer tools for doing this; the tool is included with Parallels but is a separate download for Fusion. Both converters work well with Windows images. Linux support is spotty. My advice is to avoid P2V conversion if possible. Instead, create a new guest, install the OS and applications, and then use a network connection to move data files to the new machine.

Parallels or Fusion?
Now that I've been running both platforms for some time, I generally choose Parallels when I want to work in Windows. I choose Fusion when I'm doing development work, when I'm running multicore guests, or when I need support for many different guest operating systems. I also choose Fusion when I need virtual machine images that I can share with others using VMware's free player for Windows and Linux.

Parallels is the clear winner for managing machine images and snapshots. I find myself choosing Parallels more often simply because of the snapshot manager. Similarly, Parallels' SmartSelect feature makes it easy to launch the right Windows application from within OS X. However, my use of Windows is only occasional, and it doesn't really push the machine. If my Windows work really taxed the CPU, I might opt for Fusion to run Windows as well.

Fusion is where I have all my Linux, FreeBSD, and Solaris images installed. Fusion is the only choice for SMP (symmetric multiprocessing) support or 64-bit guests. If you need to run CPU-intensive tasks in your virtual machine, Windows or Linux, Fusion's multicore support will give you better performance. Users who just want to run Outlook next to iPhoto probably won't notice a difference.

Overall, both products perform well and do what they promise. Running Windows applications alongside OS X applications is smooth on either platform. The differences between Parallels and Fusion are significant, but largely at the edge of the experience. Whichever you pick, you're sure to be impressed with virtualization on OS X.