If you plan to run Hyper-V on machines that have Intel Sandy Bridge CPUs then you will need to deploy Service Pack 1, either in the form of the add-on or integrated build for Windows Server 2008 R2 or Hyper-V Server 2008 R2. That’s according to a Microsoft blog written by “Blauge”.
This is because of a new AVX instruction in the CPU. It seems that a VM will fail to start on a host with this CPU type without SP1. You’ll get this error:
<VM Name> could not initialize
The fix is to install SP1.
According to Wikipedia, the AVX “instruction set is an advanced form of SSE and is suited for floating-point-intensive applications. The two-operand instruction limit is increased to three operands, and advanced data rearrangement functions are included. New features include mask loads, data permutes, increased register efficiency and use of parallel loads, as well as smaller code size. The AVX instruction provides up to double peak FLOPS performance compared to using SSE4 instructions on CPUs”. That’s Martian to me, to be honest, but it sounds like more CPU horsepower.