Microsoft Virtual Machine Bus (VMBus)

Microsoft Virtual Machine Bus (VMBus) is a mechanism within the Hyper-V architecture that enables logical communication in partitions. 

The VMBus works as the internal communications channel to redirect requests to virtual devices, allowing files to be dragged and dropped between the virtual machine and the host. The VMBus is also directly used in a process Microsoft calls enlightened I/O, which the company describes as a specialized high-level communication implementation of virtualization aware-protocols, including SCSI. Using the VMBus, enlightened I/O can bypass any layer of device emulation and make communication more efficient. The process requires enlightened guests that are both VMBus and hypervisor aware.