Explain different types of hardware virtualization.

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 Hardware virtualization is the method used to create virtual versions of physical desktops and operating systems. It uses a virtual machine manager (VMM) called a hypervisor to provide abstracted hardware to multiple guest operating systems, which can then share the physical hardware resources more efficiently. Hardware virtualization offers many benefits, such as better performance and lower costs.


Types of  Hardware virtualization

 They are as follows:

  1. Full Virtualization
  2. Emulation Virtualization
  3. Para-Virtualization

1. Full Virtualization

If we discuss full Virtualization, it is underlying Hardware that is entirely simulated. The Guest software does not need to perform any modifications to run their applications.

In full virtualization, there is no need for any modification to run any application. In addition, the hardware architecture completely simulates, which benefits the guest software. There is an environment, quite similar to an operating system in a server.

With the help of full virtualizations, the administrators allow running a virtual environment to change to its physical counterpart. With the help of full virtualization, the administrators can combine the new and the existing system for something efficient. So, it should be compatible with the newer system.




2. Emulation Virtualization

Moving on towards the second Virtualization type, it is known as Emulation Virtualization. In this type of Virtualization, the virtual machine simulates the Hardware, thus becoming independent of it. In this Virtualization, the guest operating system is not required to perform any modifications.

In emulation virtualization, hardware simulates by the virtual machine and it is independent. Here, the guest operating system does not require any other modification. In this virtualization, computer hardware as architectural support builds and manages a fully virtualized VM.



3. Para-Virtualization

The Hardware is not simulated in Para-Virtualization. Here, the Guest software must run its own isolated domains.

In paravirtualization, the hardware is not simulated and the guest software runs its isolated system. It is not necessary to simulate the hardware, but it utilizes an API that modifies the guest operating system.

The hypervisor provides various command, which is sent from the operating system to the hypervisor and is called hypercalls. These hypercars are further used for memory management.



Types of hardware virtualization

Multiple types of hardware virtualization exist, with processes including full virtualization, paravirtualization, and hardware-assisted virtualization.

Full virtualization: 

Fully simulates the hardware to enable a guest OS to run in an isolated instance. In a fully virtualized instance, an application would run on top of a guest OS, which would operate on top of the hypervisor and finally the host OS and hardware. Full virtualization creates an environment similar to an OS operating on an individual server. Utilizing full virtualization enables administrators to run a virtual environment unchanged from its physical counterpart. For example, the full virtualization approach was used for IBM's CP-40 and CP-67.

Other examples of fully virtualized systems include Oracle VM and ESXi. Full virtualization enables administrators to combine both existing and new systems; however, each feature that the hardware has must also appear in each VM for the process to be considered full virtualization. This means, to integrate older systems, hardware must be upgraded to match newer systems.


Paravirtualization:

 Runs a modified and recompiled version of the guest OSes in a VM. This modification enables the VM to differ somewhat from the hardware. The hardware isn't necessarily simulated in paravirtualization but uses an application program interface (API) that can modify guest OSes. To modify the guest OS, the source code for the guest OS must be accessible to replace portions of code with customizable instructions, such as calls to VMM APIs. The OS is then recompiled to use the new modifications.

The hypervisor then provides commands sent from the OS to the hypervisor, called hypercalls. These are used for kernel operations, such as the management of memory. Paravirtualization can improve performance by decreasing the amount of VMM calls; however, paravirtualization requires the modification of the OS, which also creates a large dependency between the OS and hypervisor that could potentially limit further updates. For example, Xen is a product that can aid in paravirtualization.


Hardware-assisted virtualization:

 Uses a computer's hardware as architectural support to build and manage a fully virtualized VM. Hardware-assisted virtualization was first introduced by IBM in 1972 with IBM System/370. Creating a VMM in software imposed significant overhead on the host system.

Designers soon realized that virtualization functions could be implemented far more efficiently in hardware rather than software, driving the development of extended command sets for Intel and AMD processors, such as Intel VT and AMD-V extensions.

So, the hypervisor can simply make calls to the processor, which then does the heavy lifting of creating and maintaining VMs. System overhead is significantly reduced, enabling the host system to host more VMs and provide greater VM performance for more demanding workloads. Hardware-assisted virtualization is the most common form of virtualization.

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