Paravirtualization refers to the simple virtualization technique that can be used to basically improve the performance in a guest operating system by giving sort of a direct link between the virtual machine and the underlying physical hardware

1. Author: Panait Robert
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What is Paravirtualization ?
The term Paravirtualization may be new to you, but the fact is that it
has been around for a fairly long time. Paravirtualization has existed
since 1972 in IBM's old VM operating system where it is called
DIAGNOSE code", and it is also present as a distinct feature in the
Parallels Workstation operating system under the name "hypercall".
In truth, while there are several different terms by which it has been
known over the years, paravirtualization refers to the simple
virtualization technique that can be used to basically improve the
performance in a guest operating system by giving sort of a direct link
between the virtual machine and the underlying physical hardware.
Before a guest operating system is installed inside a virtual machine, it is
recompiled in order to achieve the enhancement of the virtualization
technology through paravirtualization.
With paravirtualization, any and all software that is running on a
virtual system will be able to work directly on the underlying physical
system hardware. That is, the software itself on the virtual machine's
guest operating system will be able to make calls on the hardware
directly instead of relying on just the virtual machine to make the
necessary calls for it. Because of this, performance is increased without
the need to sacrifice any computing power.

2. Paravirtualization falls under the three main types of hardware
virtualization. As you may already know, hardware virtualization also
commonly referred to as platform virtualization, is the creation of a
virtual machine that performs as if it were an actual computer that has
some kind of an operating system installed on it.
Hardware virtualization allows software to be installed and run on
virtual machines that are separated from underlying physical hardware
resources. A computer that is running a version of the Microsoft
Windows operating system might have a virtual machine on it that is
running a version of the Gentoo Linux operating system. That is one
basic example of hardware virtualization at work.
The three types of virtualization in hardware and these are full
virtualization, partial virtualization, and paravirtualization.

3. Virtualization
In full virtualization, there is almost a complete model of the underlying
physical system resources that allows any and all installed software to
run without modification.
Partial virtualiation
In partial virtualization, not everything in the target environment
becomes simulated. Not all software programs installed on the guest
operating system can run unmodified.

4. Paravirtualization
Finally, there's paravirtualization, which as explained above, is
essentially a way to improve performance by having a software interface
working between the virtual machine and the underlying physical
hardware system itself.
Intel (Intel VT - IVT ) and AMD (AMD-V) have both released hardware
virtualization technology to facilitate the running of hardware
virtualization on computers. This technology has been designed to boost
the power of the hypervisor.
Although these two pieces of hardware virtualization technology are
separate and independent, they perform broadly the same function. As
increasing numbers of modern computers are sold with incorporated

5. hardware virtualization technology, more powerful CPUs will
continually be developed to allow for better creations of simulated
environments.
In a virtual machine, there is something called the hypervisor, which is
basically the visual interface installed on a real machine that takes care
of operations on the virtual counterparts. Now in most cases, the
hypervisor will not be accessible to the instances in a virtual machine.
Instead, it can only be accessed by those who actually have access to the
real machine itself. And even if it is possible to gain access to the
hypervisor on a virtual system, there will often be severe limitations to
what can be done with it.

6. In order to avoid going through the virtual operating system for access to
hardware whenever it is needed, one can rely on paravirtualization.
What paravirtualization does is allow users on a virtual system to avoid
going through the virtual fluff and call on the underlying physical
hardware resources directly. This helps save so much time and
computing resources.
How exactly does paravirtualization improve overall performance ?
Paravirtualization can minimize system overhead and really optimize
overall performance due to the fact that it can support the use of virtual
machines that would otherwise be underutilized in the two other forms
of hardware virtualization mentioned earlier.
Though it has many advantages, paravirtualization isn't without
limitations. For instance, paravirtualization requires the guest OS to be
customized for the virtual machine monitor which it will run on top of.
That is, in order to take advantage of paravirtualization, you first have to
make certain preparations on the virtual system as well as on the
physical system itself. You usually won’t find it included in standard
installations. However, some software companies do provide add-ons
that give the necessary abilities for all of this to become a reality.

7. If you liked this article you can find more posts about this niche on
http://www.virtualizationsoftwares.com , a site dedicated entirely to
virtualization software, where everyone will find general information
about the matter, that will help potential clients to find the perfect
program as well as reviews for the products of the main players of the
virtualization software market.
Related Articles :
What is Hardware Virtualization ? What is virtualization software?
What is Hypervisor ? What is Xen Virtualization ?