What is a Hypervisor?

Operating systems are bound to specific hardware resources. Normally, only one operating system can run on the same device. However, by virtualising the computer architecture, multiple operating systems can work simultaneously. To provide corresponding virtual environments, a Hypervisor is required. In the following article, we explain what a Hypervisor is, the types available, and its possible applications.

What is a Hypervisor?

A Hypervisor, also known as a Virtual Machine Monitor (VMM), is a software that creates, runs, and manages virtual machines (VMs). The VMM isolates the operating systems of the virtual machines and allocates resources such as CPU, RAM, or disk storage to them. It has access to the system's resources and manages them as needed.

The existing hardware acts as the host in server virtualisation. Through the Virtual Machine Monitor, the various guest systems (Guests) are assigned the resources of the host system. When new VMs are added, they can be easily integrated into the overall structure.

There are generally two types of Hypervisors:

• Hypervisor Type 1
• Hypervisor Type 2

Both types have their advantages and disadvantages, which we will discuss below.

Hypervisor Type 1

Hypervisor Type 1, also known as native or Bare-Metal Hypervisor, is installed directly on the hardware and has access to all system resources without needing an intermediary layer. It acts as the host operating system and distributes VM resources directly from the hardware. The VMM requires specific drivers for this purpose.

A major advantage of this solution is the better performance, as the Hypervisor can access the hardware substance without restrictions. Therefore, Hypervisor Type 1 is commonly used in large enterprises or data centres. Web hosting providers, in particular, predominantly utilise this solution as the servers they offer are Bare-Metal Servers due to their superior performance.

However, it is important to note that this solution requires higher maintenance and management efforts and also demands basic knowledge, such as operating the console.

The following software is suitable for Hypervisor Type 1: KVM, Microsoft Hyper-V, and VMware vSphere. KVM was integrated into the Linux kernel in 2007. Therefore, modern Linux systems are already delivered with a Hypervisor Type 1.

Hypervisor Type 2

Hypervisor Type 2, also known as hosted Hypervisor, does not interact directly with the hardware. Instead, it is installed as an additional layer on a conventional OS.

Thus, the hardware has its own host operating system. The Virtual Machine Monitor separates the guest systems from the host. Each virtual machine can be equipped with its own operating system.

Hypervisor Type 2 manages resources by interacting with the host system. Therefore, it cannot access the complete hardware substance.

A major advantage of a Type 2 VMM is the lower maintenance and administration effort, as no additional drivers are required. Additionally, a Hypervisor Type 2 offers greater flexibility since the software is directly installed on the host's operating system. The host system itself is capable of running additional applications at the same time.

Essentially, a Type 2 Virtual Machine Monitor is particularly suitable for individual desktop PCs where different operating systems need to be isolated or run simultaneously.

However, a disadvantage of this solution is the lower performance compared to Type 1. Since the Type 2 hypervisor sits as an additional layer on top of the host OS, it can only access resources that the system itself does not use.

Known applications that function as Type 2 hypervisors include Oracle Virtualbox or VMware Workstation.

Graphic: schematic representations of the difference between Hypervisor Type 1 and Type 2

Applications of Hypervisors

There are many areas where a hypervisor is used.

Firstly, virtualisation can enhance the security of the host system. The hypervisor allows multiple operating systems to run simultaneously and isolated from each other. For example, if a guest system is infected by a virus, all other systems remain unaffected.

Additionally, sensitive data can be stored on the same hardware and protected from access by a connected network such as the internet.
If a server is running simultaneously with a desktop operating system on the same hardware, desktop data can be protected by isolation in a separate VM. However, the parallel running Linux- or Windows server should also be protected from hacking attempts.

However, if the host system is hacked, all VMs managed by it may also be affected.

Furthermore, applications that require different operating systems can be run simultaneously on the same hardware. Users can also test applications in a virtual environment before deploying them to a live system. Moreover, setting up and securing a VPS hosting is possible with the help of a hypervisor.

Virtual servers are offered with various virtualisation techniques, including:

OpenVZ VPS hosting
Virtuozzo VPS hosting
KVM VPS hosting
Xen VPS hosting
VMWare VPS hosting

Programs serving as Virtual Machine Monitors are playing an increasingly important role in the commercial sector. In particular, web hosting providers work with virtualisation solutions, as otherwise they would have to provide separate hardware for each rented server. Virtual servers, on the other hand, save resources and costs. This allows even less common products like web packages based on the Litespeed Web server to be offered cost-effectively.

However, for companies looking to store software or data on different servers, a Virtual Machine Monitor is also of interest. In addition to the security aspect mentioned above, virtualisation can also control access rights. Furthermore, sensitive data can be isolated on separate guest systems and hidden from unauthorized access by a hypervisor.

Our article is based on our own experiences and research as well as information from external sources.

Sources & further links on the topic:
https://www.parallels.com/de/blogs/hypervisor/ (Information from Parallels on the topic of Hypervisor)
https://www.storage-insider.de/was-ist-ein-hypervisor-a-842084/ (Article on Hypervisor on Storage-Insider)
https://www.linux-kvm.org/page/Main_Page (Official Wiki of the KVM Community)
https://www.redhat.com/de/topics/virtualization/what-is-KVM (Information from the owner of the KVM developer)
https://xenproject.org/ (Official website of the Xen Project)
https://www.linux-magazin.de/ausgaben/2017/12/xen/ (Article on Xen in the Linux Magazine)
https://www.vmware.com/de.html (Company website of VMware)
https://vmware-forum.de/ (Largest German VMware Forum)
https://www.virtuozzo.com/ (Official Virtuozzo website)
http://download.parallels.com/doc/pvc/PVC_DataSheet_Ltr_EN.pdf (Information on Parallels Virtuozzo Containers)

Image credit:
Gerd Altmann on Pixabay