Those who remember Microsoft Virtual Server should know that Hyper-V is a complete rewrite and is a different piece of software. Microsoft Virtual Server is a host based virtualization solution, which is too slow for a production enterprise environment. On the other hand, Hyper-V is a hypervisor based virtualization solution that's very well suited for high performance production environments.
Hyper-V CPU and I/O PerformanceHyper-V requires hardware assisted virtualization such as Intel VT-X or AMD-V which makes virtualization run fast. The consequence of requiring CPU based virtualization assistance also means Hyper-V will not run on old hardware and that it will only work on 64-bit Windows Server 2008.
I/O performance was independently tested by storage vendor Qlogic with results that show Hyper-V performed at 88% to 99% of native performance, depending on the storage subsystem used.