Q. I' migrated a Windows Server 2003 virtual machine (VM) from Virtual Server to Hyper-V and allocated two virtual CPUs to the VM, but I only see one CPU within the guest OS. What's wrong?

A. Server 2003 uses different hardware abstraction layers (HALs) for single processors than for multiple processors. Under Virtual Server, the Server 2003 OS would use the single processor HAL, and it will continue to use that HAL after migration to Hyper-V with multiple virtual CPUs assigned to it. To resolve this problem, you need to update the HAL within the Server 2003 guest OS. See this Microsoft page for more information on changing the HAL.