Different Hypervisor designs in Type 1 hypervisor's
In the type 1 VMM/hypervisor a.k.a bare metal hypervisor there are two categories of Hypervisor designs.
a. Microkernelized Hypervisor Design
Ex: Microsoft Hyper V
b. Monolithic Hypervisor Design
Ex: VMware vSphere
Device drivers does not need to be hypervisor aware and they are on the controlling layer. So a wide range of Hardware can run this kind of a Hypervisor and there is less overhead on the hypervisor itself.
At the same time this needs an Operating System to be installed to initialize the hypervisor layer, and any attack or a fault of that controlling layer operating system can affect the whole hypervisor and bring down all the virtual machines.
Monolithic Hypervisor Design:
In this design the device drivers run at the same layer as the VMM/Hypervisor, hence the hardware and I/O devices should be Hypervisor aware in other words device drivers to be developed for the hypervisor so this results only a certain set of certified hardware can only run this kind of a hypervisor.
No operating system is required to fork lift this hypervisor this makes the hypervisor stable, No security patches are needed for components running in the "Controlling Layer."
Now that we have understood about type 1 hypervisor's what is type 2.
A type 2 hypervisor runs as a software on top of an existing Operating system.
Ex: VMware Workstation, VMware Fusion etc.