A. The Release Candidate of Windows Server 2008 R2 introduced two new features for Hyper-V that are available if the hardware has support. At time of writing, not many NICs have this support, but wider support is expected in the future.
VM-Chimney (TCP Offload) allows the CPU workload associated with TCP/IP traffic to be offloaded to the physical NIC, reducing processor usage and increasing network performance. This has been available for physical (host) OSs but is now available for guest OSs.
VMQ is a technology that allows the physical NIC to create unique virtual network queues for each virtual machine (VM) on the host, allowing network packets to be passed directly from the hypervisor to the VM. This reduces a lot of overhead normally associated with network traffic.
If a NIC has support for both VMQ and VM-Chimney, VMQ will be used.
Related Reading:
Check out hundreds more useful Q&As like this in John Savill's FAQ for Windows. Also, watch instructional videos made by John at ITTV.net.