Hyper-V allows x64 versions of Windows to host one or more virtual machines, which in turn contain a fully configured operating system. These “child” systems are treated as partitions. The term is otherwise known from hard disk partitioning - and Hyper-V virtualization works in a similar way. Each virtual machine is an isolated unit next to the “parent” partition, the actual operating system.
The individual partitions are orchestrated by the hypervisor. The subordinate partitions can be created and managed via an interface (Hypercall API) in the parent system. However, the isolation is always maintained. Child systems are assigned virtual hardware resources but can never access the physical hardware of the parent.
To request hardware resources, child partitions use VMBus. This is a channel that enables communication between partitions. Child systems can request resources from the parent, but theoretically they can also communicate with each other.
The partitions run services that handle the requests and responses that run over the VMBus. The host system runs the Virtualization Service Provider (VSP), the subordinate partitions run the Virtualization Service Clients (VSC).