Hyper-V is the technology with code name Viridian. Previously this was known as Windows Server Virtualization. It implements virtualization based on a hypervisor. The hypervisor allows multiple operating systems to share on resource. This is a different level of abstraction than multitasking. The hypervisor actually protects the operating systems from failures other instances encounter.
Initially the Hyper-V was released in beta as part of Windows Server 2008. There are now two release versions of this product. There is a stand alone version. And there is the version that is a part of Windows Server 2008 R2.
The stand alone version is called Microsoft Hyper-V Server 2008 R2. This version is free. It has limited Windows services. It also makes you use the command line interface to do management. The other version is part of Microsoft Windows Server 2008 R2. This part is called the Microsoft Hpyer-V server. It is a core part of Windows Server 2008. It boasts point and click administration.
The parent operating system must be Windows Server 2008. Child partitions host guest operating systems that run virtually. These virtual partitions cannot directly access the physical hardware. The supported guest operating systems include Windows Server 2000/2003/2008, Windows 7, Windows Vista, and SUSE/RedHat Linux.
Hyper-V does not natively support USB devices. It also does not support sound in the guest operating systems. If you use the display drivers from