With Hyper-V, the parent partition
or the root partition
runs on Windows Server 2008 x64 Server Core installation or Windows Server 2008 x64 Full installation with the Hyper-V role installed and sits on top of the hypervisor.
The parent partition (not the hypervisor) manages the I/O devices. To provide virtual machines with access to those devices, Hyper-V supports a high-speed interconnect referred to as the VMBus
. Virtual devices for each VM, such as network and storage adapters, can
communicate with the parent partition through the VMBus. The parent partition receives those requests through the VSP
s (Virtualisation Services Provider) and directs them to the underlying physical devices via the I/O stack of the parent partition. This model requires device drivers for the physical devices to be installed inside the parent partition.
Most device specific drivers and utilities created for Windows Server 2008 x64 work as-is and do not require any changes when Hyper-V is enabled.
So “virtual devices for VMs, can communicate with the parent partition through the VMBus”. But what criteria determines if communication passes through the VMBus?!
Guest operating systems require specialized drivers (VSCs – Virtualisation Services Consumers) provided by Microsoft in order to access the VMBus. The drivers are specific to the type of device that is presented to the guest operating system through the VM configuration (with the Hyper-V Manager) and are installed as a part of the Integration Services that are available for Hyper-V supported guest operating systems.