Hypervisor

• The virtual networking components would not be virtualized if it weren't for the hypervisor.
• The hypervisor sits between the hardware or operating system and the VM to allow for resource sharing, time sharing of VMs to the physical hardware, and virtualization of the guest operating systems (VMs).
• The hardware that the hypervisor is installed on is called the host, and the virtual machines are called guests.
• There are three different types of hypervisors.
• A type 1 hypervisor:

  • It is software that runs directly on the hardware
  • Its only purpose is to share the hardware among VMs running as the guest operating system. (a partitioning of hardware)
  • Examples: Xen/Citrix XenServer, VMware ESXi, and Hyper-V. Although Hyper-V fits into the third category of hypervisors, it is still considered a Type 1 hypervisor.
• A type 2 hypervisor: a software that runs on the host operating system.

  • It runs as a process in the host operating system.
  • Type 2 hypervisors do talk directly to the CPU via Intel VT or AMD-V extensions, depending on which vendor you are using.
  • Memory utilization is similar to CPU utilization, but the host operating system parlays the requests via Direct Memory Access (DMA) calls.
  • All other hardware is proxied through the host operating system.
  • Examples: VMware Workstation, VirtualBox, Parallels for maxOS, and the open-source QEMU.
• Hybrid hypervisors

  • They function outside of the norm of cloud computing hypervisor models.
  • They require a host operating system but function as a Type 1 hypervisor.
  • Example: Hyper-V requires the Microsoft operating system to be installed, but the host operating system is a guest called the parent partition. It is treated the same as guest or child partitions, but it is required for management of the hypervisor.
• Examples of hybrid hypervisors:

  • Linus Kernel-based Virtual Machine (KVM), FreeBSD bhyve (pronounced beehive), and Microsoft Hyper-V.