When it comes down to it, which of the free virtualization Offerings from Microsoft would you choose? Virtual PC 2007 or Virtual Server 2005 R2 SP1? Before choosing, you should take into consideration Microsoft's perspective over the two products. In this context, while both Virtual PC 2007 and Virtual Server 2005 are examples of Microsoft virtualization technology, they have different destinations. Virtual PC is addressed at users deploying hardware emulating technology bundled with the Windows client operating system. Virtual Server is designed to integrate seamlessly with the company's Windows Server platform.

"Virtual PC offers an intuitive, local UI designed for a single user while Virtual Server offers a Web Administration application allowing multiple users to administer Virtual Servers remotely. Virtual Server is designed with extensibility in mind and includes a fully documented COM interface in the Virtual Server Programmer's Guide. So, if you're interested in developing your own scripts to configure, create virtual machines, Virtual Server is the way to go. Virtual Server is heavily threaded and designed to take advantage and scale on multi-processor computers with large amounts of memory. In fact, Virtual Server can use up to 256 GB of physical memory with the latest version," revealed the Windows Virtualization Team.

Essentially, Virtual PC and Virtual Server need virtual machines to function. In this sense, Microsoft has ensured that the virtual hard disks and VMs are fully compatible across the two products. Still, there are a few caveats to pay attention to. For example, emulated sound cards in virtual machines are only supported on Virtual PC and not on Virtual Server. VMs designed to be swapped between Microsoft's two examples of virtualization technology should preferably be built with the emulated sound card disabled in Virtual PC to avoid conflicts and error.

"Virtual Server provides SCSI support while Virtual PC does not. If you create a virtual machine with virtual SCSI disks on Virtual Server, the SCSI disks will be ignored if you move the virtual machine to Virtual PC. Although Virtual Server allows for virtual machines with multiple CD-ROM drives, Virtual PC supports virtual machines with only one CD-ROM drive. Save-state (.vsv) files between Virtual PC and Virtual Server are incompatible. When moving virtual machines between Virtual PC and Virtual Server, the virtual machine's network will be disconnected. You will need to configure the virtual machine's network connectivity appropriately," the Windows Virtualization Team added.