What is Hypervisor in Virtualization and what are it's types

Hypervisor and it's types

Virtualization is very trending topic today in IT world. We always talk about virtualization but we never talk about the technology which is makes virtualization possible and that is Hypervisor.

Today we are going to talk about Hypervisor. A hypervisor essentially separates the operating system and

 applications in a computer from the underlying physical hardware. This is how it enables virtualization, by giving the physical host machine the ability to operate multiple VMs (Virtual Machines) on the same system. Having these multiple VMs as guests help optimise the usage of computing resources, such as memory, network bandwidth and more. 

Although Virtual Machines run on the same host machine, they are still separated from each other. This allows every Virtual Machine a greater degree of privacy. It also safeguards them from instances of errors, crash or malware attacks that happen to other Virtual Machines on the same system.

Furthermore, Virtual Machines by nature are very mobile. Since they are independent of the underlying hardware, these VMs can be moved between local or remote virtualized servers with ease (as opposed to more traditional applications that are tied down to physical hardware).

There are two types of Hypervisor:

• Type 1 Hypervisor (bare metal)
• Type 2 Hypervisor (hosted hypervisors)

Type 1 Hypervisor (Bare metal)

This means that it runs directly on the physical hardware of the host machine — it doesn’t have to load an underlying Operating System before that. Due to the fact that Type 1 hypervisors have direct access to the underlying hardware (and no other Operating Systems and device drivers to content with) this type of Hypervisor is considered to be the best performing and most efficient for enterprise computing.

Example: Citrix/Xen Server, Microsoft Hyper-V and VMWare ESXi

Type 2 Hypervisors(hosted hypervisors)

As name suggests here "hosted hypervisor" , these hypervisors are typically installed on host operating system. So it relies on machines OS to perform some operations like managing CPU, memory, resources.

Type 2 hypervisors are typically found in environments with a small number of servers.

What makes them convenient is that you do not need a management console on another machine to set up and manage virtual machines. You can do all of this on the server where you install the hypervisor. They are not any different from the other applications you have in your operating system.

When you launch a virtual machine, you get another window to perform all tasks.
There is no need to install separate software on another machine to create and maintain your virtual environment. You simply install and run a type 2 hypervisor as you would any other application within your OS. With it, you can create snapshots or clone your virtual machines, import or export appliances, etc.
Here is one example of a type 2 hypervisor interface (VirtualBox by Oracle):

When you assign 8GB of RAM to a VM, that amount will be taken up even if the VM is using only a fraction of it. If the host machine has 32GB of RAM and you create three VMs with 8GB each, you are left with 8GB of RAM to keep the physical machine running. Creating another VM with 8GB of ram would bring down your system. This is critical to keep in mind, so as to avoid over-allocating resources and crashing the host machine.

Example: Oracle VirtualBox, VMWare workstation, Windows Virtual PC.
 

At the end

Today, most hypervisors used in production are Type 1 hypervisors. However, there are still a few IT environments that prefer Type 2. Type 1 hypervisors are more common in production due to the low overhead. However, the low cost and ease of installation of a Type 2 hypervisor make it an ideal option for home labs or other test environments. Mostly people use Type 2 on their laptop for learning and other stuff.