Windows Virtualization is the next generation of virtualization solutions offered by Microsoft. Here is a quick list on how it compares to Virtual Server 2005 R2 SP1:

• Supported Hardware: Virtual Server 2005 R2 SP1 runs on both x86 and x64 architectures. Windows Virtualization will be x64 ONLY.
• Virtual Machine Support: Virtual Server supports 32–bit virtual machines. Windows Virtualization supports both 32 and 64–bit Virtual Machines
• Virtual Machine Memory Support: Virtual server can allocate up to 3.6GB per VM. Windows Virtualization will be able to assign up to 32GB per VM
• Hot add: Virtual Server does not support adding hardware to a virtual machine while it is running. Windows Virtualization supports hot add of memory, processors, storage, and networking devices.