Type 1 bare metal vs Type 2 hosted hypervisors, and the VT-x extension: Basics of virtualization
435In this video series I present a simple and straighforward explanation on different core topics of virtualization. In this video we compare the Type 2 so called "hosted" hypervisors with Type 1 so called "bare metal" hypervisors. Furthermore, the importance of the ®Intel VT-x virtualization extension technology is explained. Through VT-x the hypervisor can expose the CPU and the memory controller to virtual machines installed on top of the hypervisor. In the meantime, even further hardware extensions have been introduced by CPU manufacturers like the VMD-q, VT-d (IOMMU) and SR-IOV, which will be discussed in upcoming videos.
Although mainframes have used native virtualization since the early 60s, on the more common x86 platform virtualization was first introduced in form of Type 2 hypervisors. In the case of Type 2, the hypervisor (for example VirtualBox or VMware Workstation Player) is running as an application on top of a host operating system. Due to the complex software layers involved, and especially because of the lack of advanced hardware-assisted paravirtualization features, such Type 2 hypervisors are mainly used for small scale virtualization project for home use.
To expose more hardware to the virtual machines, to improve performance and reliability, and to have more tight control over the hardware, so called "bare metal" Type 1 hypervisors have been introduced. Type 1 hypervisors like VMware ESXi or Hyper-V from Microsoft® take advantage of the VT-x hardware extension, which implements hardware features in the CPU such, that the hypervisor can perform advanced function on the memory controller unit, and access resources (hardware protection rings) which were not available before the introduction of VT-x. This makes it possible to do so called hardware-assisted virtualization instead of the full-software virtualization. The equivalent technology from AMD is the AMD-v extension. In industrial applications and in companies Type 1 hypervisors are now a de-facto standard, and they are a staple in every computer room or data center.
As a simple definition, one can look at a hypervisor as a software, which allows multiple independent instances of different operating systems to be installed and to run simultaneously by sharing resources on the same physical hardware. Due to the separation facilitated by the hypervisor between different OS running as virtual machines on the same hardware, one can achieve improved security and better control over the virtualized applications.
Due to their different nature, Type 1 hypervisors are using a microkernel, wheres Type 2 hypervisors are installed on top of a thick layer of a full OS.