What is Paravirtualization?

Paravirtualization is a computer hardware virtualization technique that allows virtual machines (VMs) to have an interface similar to that of the underlying or host hardware. This technique aims to improve the VM’s performance by modifying the guest operating system (OS).

With paravirtualization, the guest OS is modified, so it knows that it is running in a virtualized environment on top of a hypervisor (the hardware running the VM) and not on the physical hardware.

Other interesting terms…

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When we talk about virtualization in the context of IT, it refers to the process of creating a software representation of an application, a server, a network, or a storage device. In software development, for instance, virtualization is a cost-effective way to test if bug fixes or updates to an application work on different OS environments.

On a larger scale, virtualization allows organizations to run multiple applications and OSs on a single server, making the process more efficient and budget-friendly.

Several virtualization techniques exist, one of them is paravirtualization. The video below briefly explains how this particular technique works.

To better understand the answer to “What is paravirtualization?” let us compare it with another technique—full virtualization.

Differences between Full Virtualization and Paravirtualization

Full virtualization is among the first and most common types of virtualization that enables VMs to simulate the underlying hardware completely. Any software and OS supported by the host hardware can thus run in the VM.

Users can have multiple guest OSs running simultaneously, and each would be fully isolated from the physical hardware. Full virtualization uses binary translation to execute operations. So, every process the VM performs is translated into the host’s language code through binary translation. Because of this additional process, operations in full virtualization are slow.

In paravirtualization, operations are performed through hypercalls or system calls from the guest OS directly sent to the hypervisor instead of the host’s physical hardware. Since the guest OS has direct access to the host hardware, no binary translations are required. Instructions within the paravirtualization environment are, therefore, performed faster compared with those in full virtualization. VMs in paravirtualization are also not entirely isolated.

How Does Paravirtualization Work?

To enable hypercalls in paravirtualization, modifications have to be done with the OS kernel, the core program that controls the whole OS. This lets the guest OS know that it is in a virtualized environment sitting on top of a hypervisor. When a user executes a command in the guest OS, it is communicated through a hypercall to the hypervisor. The chart below shows a simplified flow of how paravirtualization works.

What Are the Advantages and Disadvantages of Paravirtualization?

One of the advantages of paravirtualization is that it executes instructions a lot faster. The concept is similar to having the ability to speak Japanese fluently. Going around Japan would be easier since communication is smoother and faster.

On the other hand, full virtualization is comparable to the need for a translator. The ease of your travel would largely depend on the translator’s efficiency.

Although paravirtualization offers improved speed and performance, it has downsides, too. For one, it is less compatible, as not all systems support paravirtualization. Remember that setting up paravirtualization also requires OS kernel modification.