There are several versions of Hyper-V, Microsoft’s Type 1 hypervisor. The most complete version is found in Windows Server 2008.

Note, however, that Hyper-V is an x64-only function of Windows Server 2008. This means that it is only available as a role within the x64 editions of Windows Server 2008.

Although Hyper-V components are also available in x86 or 32-bit editions of Windows Server 2008, only the administration function of Hyper-V can be run on these platforms; the hypervisor itself cannot run on a 32-bit platform.

Also note that the Web edition of Windows Server 2008 does not include any version of the Hyper-V function, nor do the versions that specifically state “without Hyper-V.”

In fact, the fully functional Hyper-V role can only be found in the following editions:

• Windows Server 2008 Standard x64 edition - Provides support for the Hyper-V role. License includes support for one physical server installation plus one guest operating system or virtual machine.
• Windows Server 2008 Enterprise x64 edition - Provides support for the Hyper-V role as well as Hyper-V failover clustering for high availability. License includes support for one physical server installation plus four guest operating systems or virtual machines.
• Windows Server 2008 Datacenter x64 edition - Provides support for the Hyper-V role as well as Hyper-V failover clustering for high availability. License includes support for one physical server installation plus unlimited guest operating systems or virtual machines. Note that the Datacenter edition is licensed on a per-processor basis.

In addition to obtaining the appropriate edition of Windows Server 2008 to run the Hyper- V role, you must ensure that you have the right hardware platform. Hyper-V, because it is a hardware- based hypervisor, must run on a 64-bit system with both hardware- assisted virtualization and data execution prevention (DEP) enabled.

Systems that meet these requirements are x64 systems—not Itanium systems. x64 processors are simply a 64-bit extension of x86 or traditional 32-bit technology. Itanium processors are custom 64-bit processors produced by Intel to support special resource-intensive workloads. x64 processors are available from both Intel and AMD.

Intel x64 processors rely on Intel Virtualization Technology (Intel VT). AMD processors rely on AMD Virtualization (AMD-V). Both processors require specific Basic Input/Output System (BIOS) settings to control or enable the hardware-assisted virtualization function.

This function supports hypervisors by providing direct interaction between the hypervisor and all system hardware. The hardware-assisted virtualization feature must be enabled within the system’s BIOS for the hypervisor to operate.

As with many Windows Server 2008 roles, Hyper-V can be run in either the full installation or the Server Core installation. Keep in mind that running Hyper-V in a full installation of Windows Server 2008 will reduce the resources available to virtual machines because the full installation requires more resources to operate than the Server Core installation.

In addition, the full installation will have an impact on virtual machine availability because it includes more components—Windows Media Player, Windows Photo Gallery, Internet Explorer, and so on—that require software updates.

Each time you must update the base operating system and reboot the host server, you must shut down all of the virtual machines it may run—even if only temporarily. This significantly reduces the availability of virtual machines.

On the other hand, Server Core has been designed to run without a graphical interface. It provides both a reduced attack surface and an improved platform for virtualization because it runs fewer processes and applications than the full installation.

Yet it supports all of the functionality required to support the operation of a production hypervisor, including failover clustering, when based on the appropriate editions of Windows Server 2008. For these reasons, Server Core is the ideal platform for Hyper-V in production.

Note, however, that because of its lack of a graphical interface, most organizations choose to manage Server Core installations remotely through the use of the Windows Server 2008 Remote Server Administration Tools (RSAT).

RSAT can be installed on either Windows Vista or the full installation of Windows Server 2008. This does not mean that you cannot run Hyper-V on the full installation of Windows Server 2008.

Just keep in mind that because of the higher overhead involved with this installation, you should keep instances of Hyper-V on full installations out of the production datacenter and reserve them for testing or development environments. This will reduce the impact the full installation has on the virtual machines you run.