What is the hypervisor

An hypervisor is a software, firmware or hardware for computers that creates and runs virtual machines. 

This is also called a virtual machine monitor (VMM).

The functionality of an hypervisor is to isolate the operating system, allowing the creation and management of resources.

The physical hardware, when used as an hypervisor, is defined as host, while the VMs that use the resources are called guests.

The hypervisor is paired with three main resources:

• CPU;
• Memory;
• Storage.

For execution, however, all hypervisors must have several components:

• Memory manager;
• Process scheduler;
• Input/output stack;
• Device drivers;
• Security manager;
• Network stack.

To each virtual machine, the hypervisor provides all the allocated resources to manage the scheduling of VM resources in relation to physical resources.

Let's take an example.

The physical hardware takes care of executing all the received commands, while the hypervisor manages the scheduling.

So, the CPU executes all requests from the VMs.

Types of hypervisors

There are two main types of hypervisors: type 1 and type 2.

Type 1 hypervisor

A type 1 hypervisor runs directly on the host hardware to manage guest operating systems.

It replaces the host operating system, and VM resource scheduling is done directly on the hardware through the hypervisor. 

This type of hypervisor is most common in a data center and other server-based environments.

Type 2 Hypervisor

A type 2 hypervisor is also called a hosted hypervisor.

It runs on a conventional operating system like software or an application.

Its function is to abstract guest operating systems from the host operating system.

The scheduling of VM resources is based on the host operating system, which in turn runs based on the hardware. 

This hypervisor is ideal for all individual users who run multiple operating systems on a personal computer. 

Thanks to a hypervisor, it is possible to run different operating systems simultaneously, ensuring that they share the same virtualized hardware resources.