Let me start the article by describing what is a hypervisor to understand the different types of virtualization schemes.
What is a hypervisor?
A hypervisor or virtual machine monitor (VMM) can be defined as a form of virtualization software used in Cloud hosting that allows to securely partition resources of a computer into one or more virtual machines (Marinescu, 2017). The operating system that runs under the control of the hypervisor is called the guest operating system and is not run on the hardware directly. This technique allows that various guest operating systems can operate on a single hardware platform concurrently (GeeksforGeeks, no date). Furthermore, hypervisors enforce isolation across the systems running, which enhances security. It manages how the different operating systems running uses the underlying hardware resources and also monitors the performance of the systems making adjustments if it detects degradation in the performance (Marinescu, 2017). Hypervisors are fundamental to cloud computing because it allows multiple services to share the same platform.
Type 1 vs. Type 2
According to IBM Cloud Education (2019), there are two significant categories of hypervisors called type 1 and type 2.
Type 1 is usually known as “Native hypervisor” or “Bare metal hypervisor”. This type of hypervisor runs directly on the underlying physical hardware of the computer. It interacts directly with the computer’s CPU, memory, and physical storage. Moreover, it takes the job of the host operating system (IBM Cloud Education, 2019).
Using this type of hypervisor has its advantages and disadvantages: they are highly efficient because they run on the physical hardware and provide enhanced security; there is nothing between the hypervisor and the hardware that could compromise the security by attacks (Vembu, 2019). However, they need a separate virtual machine to administer the different VMs and control the hardware of the host (IBM Cloud Education, 2019). Some examples of Type-1 are Microsoft Hyper-V, Citrix Hypervisor (Xen Server), VMware vSphere with ESX/ESXi.
The type-2 hypervisor, usually known as hosted hypervisor and the main difference with the type-1 is that runs on the operating system of the underlying host (IBM Cloud Education, 2019). In other words, the software is installed on the operating system that runs on the machine. All calls to the hardware are done through the operating system. They are straightforward to manage, and it is not necessary to install additional applications to control virtual machines (Vembu, 2019).
Some examples of Type-2 hypervisors are Oracle Virtual Box, VMware Workstation/Fusion, and Parallels.
Cloud Vendors Hypervisors
AWS has multiple hypervisors running on top of their servers. For many years they have relied on type-1 hypervisor called XEN, but for a few years, they have created their own based on Linux KVM hypervisors called Nitro (Sharwood, 2017). Nitro is a lightweight hypervisor use to maximize performance. You can find more info in the following link: https://aws.amazon.com/ec2/nitro/
Microsoft Cloud Azure has a custom type of hypervisor called Azure hypervisor based on their Hyper-V technology (Cloudmonix, 2015).
Cloudmonix (2015) What is the Azure Hypervisor? [Online] Available at: https://cloudmonix.com/blog/what-is-azure-hypervisor/ (Accessed 28 March 2020)
GeeksforGeeks (no date) Hypervisor [Online] Available at: https://www.geeksforgeeks.org/hypervisor/?ref=lbp (Accessed 28 March 2020)
IBM Cloud Education (2019) Hypervisors [Online] Available at: https://www.ibm.com/cloud/learn/hypervisors (Accessed 28 March 2020)
Marinescu, D (2017) Cloud Computing: Theory and Practice Solutions to Exercises and Problems. Morgan Kaufmann.
Sharwood, S (2017) AWS adopts home-brewed KVM as new hypervisor [Online] https://www.theregister.co.uk/2017/11/07/aws_writes_new_kvm_based_hypervisor_to_make_its_cloud_go_faster/ (Accessed 28 March 2020)
Vembu (2019) Type-1 and Type-2 Hypervisors explained [Online] Available at: https://www.vembu.com/blog/type-1-and-type-2-hypervisor/ (Accessed 28 March 2020)