Hyper-V Software Requirements

Hyper-V is a feature of Windows Server 2008 x64 Edition only. There’s no support for Hyper-V in the x86 (aka 32-bit) Edition or the Itanium versions of Windows Server 2008. The x64 Edition is required for a couple of reasons:

Kernel address space The 64-bit version of Windows Server 2008 provides a much larger kernel address space as compared to the 32-bit edition. This directly translates into the support of larger processes, which is crucial for virtualization.

Large amount of host memory Hyper-V supports up to 1 TB of RAM on the host. x86 versions of Windows Server 2008 support only up to 64 GB of RAM on the host, which would severely limit the number of VMs you could run.

We’re frequently asked to explain the differences with Hyper-V between versions of Windows Server 2008. There’s no difference—the features of Hyper-V are the same, regardless of whether you’re running the Standard, Enterprise, or Datacenter product. However, differences in the versions of Windows Server 2008 affect key virtualization scenarios:

Processor sockets Windows Server 2008 Standard Edition is limited to four sockets, whereas Enterprise Edition supports eight sockets.

Memory Windows Server 2008 Standard Edition supports up to 32 GB of RAM, and
Windows Server 2008 Enterprise Edition supports up to 2 TB of RAM. Failover clustering Windows Server 2008 Standard Edition doesn’t include the failover clustering functionality required for quick migration.

Windows Server 2008 includes the rights to run virtual images of the installed operating system. The number of those virtual images is tied to the edition.

Source of Information : Sybex Windows Server 2008 Hyper-V Insiders Guide to Microsofts Hypervisor