In a nutshell, there are two types of hypervisors: type 1, which runs directly on the hardware without requiring a host operating system, and type 2, which runs on top of an existing operating system.

Whereas most Type-2 hypervisors allow you to interface I/O devices with your virtual machines using USB passthrough, granting VMs access to the PCI devices is a different story altogether.

A client-side hypervisor is a virtual machine monitor (VMM) that resides in and virtualizes a user's computer (see client virtualization). Type 1 hypervisors are the computer's master control program.