Virtualization enables the creation of an abstraction layer that maps a logical address to a physical resources thus hiding the complexity & ensuring that the changes to the underlying system do not affect the client requesting a service.

Virtualization allows efficient management of resources as the mapping for virtual resources is both dynamic & fail.

Need for virtualization:

Server virtualization enables different OS to share the same network & make it easy to move OS between different networks without affecting the applications running on them. This allows portability of application.

Virtualization allows many instance of application to be created thus allowing them to scale up & down as per requirement. Virtualization enables load balancing thus allowing companies to handle peak loads.

Storage virtualization enables efficient utilization of existing resources. Allows services to be provided over internet.

Server virtualization:

Server virtualization can be defined as the conversion of one physical server into several individual & isolated virtual spaces that can be taken up by multiple users as per their respective requirements.

This virtualization is attained through a software application, thereby screening the actual numbers and identity of physical servers.

The age-old concept has found a revival in the recent times due to a need for space consolidation, efficiency in usage of

server capabilities, and introduction of associated notions like cloud computing, and Software as a Service (SaaS).

Modern times have seen virtualization as a rapidly emerging plateau of enhanced efficiency & performance, and this is amplified in the case of server spaces.

Server virtualization leads to space consolidation, and efficient & effective usage of server resources & capabilities.

Moreover, the redundancy practice of running one application on multiple systems is a boon for commercial sector and software programmers.

Also, the assistance offered in disaster recovery, server administration, and system upgrading are all supporting factors in server virtualization.

Application virtualization:

Application virtualization refers to running an application on a thin client; a terminal or a network workstation with few resident programs and accessing most programs residing on a connected server.

The thin client runs in an environment separate from, sometimes referred to as being encapsulated from, the operating system where the application is located.

Application virtualization fools the computer into working as if the application is running on the local machine, while in fact it is running on a virtual machine (such as a server) in another location, using its operating system (OS), and being accessed by the local machine.

Incompatibility problems with the local machine’s OS, or even bugs or poor quality code in the application, may be overcome by running virtual applications.

Application virtualization attempts to separate application programs from an OS with which it has conflicts, even causing systems to halt or crash.

Other benefits to application virtualization include:

Requiring fewer resources compared to using a separate virtual machine.

Allowing incompatible applications to run on a local machine simultaneously.

Maintaining a standard, more efficient, and cost-effective OS configuration across multiple machines in a given organization, independent of the applications being used.

Facilitating more rapid application deployment.

Facilitating security by isolating applications from the local OS.

Easier tracking of license usage, which may save on license costs.

Allowing applications to be copied to portable media and used by other client computers, with no need for local installation.

Increasing ability to handle high and diverse/variable work volume.

However, there are limitations to application virtualization. Not all applications can be virtualized, like applications

requiring device drivers and 16-bit applications running in shared memory space.

Some applications must become closely integrated with the local OS, such as anti-virus programs, as they are very difficult to run with application virtualization.

Application virtualization is used in a wide variety of applications, including banking, business scenario simulations, e-commerce, stock trading, and insurance sales and marketing.

There are two types of application virtualization: remote and streaming.

Remote applications run on a server. End users view and interact with their applications over a network via a remote display protocol.

The remote applications can be completely integrated with the user’s desktop so that they appear and behave the same as local applications, through technology known as seamless windows.

The server-based operating system instances that run remote applications can be shared with other users

(a terminal services desktop), or the application can be running on its own OS instance on the server (a VDI desktop).

A constant network connection must be maintained in order for a remote application to function.

With streaming applications, the virtualized application is executed on the end user’s local computer. When an application is requested, components are downloaded to the local computer on demand.

Only certain parts of an application are required in order to launch; the remainder can be downloaded in the background as needed.

Once completely downloaded, a streamed application can function without a network connection.

Various models and degrees of isolation ensure that streaming applications will not interfere with other applications, and that they can be cleanly removed when closed.

Presentation Virtualization:

A technology that Microsoft likes to lump into its virtualization definitions is Presentation Virtualization, or as it’s more commonly known, Terminal Services (or its newer name, Remote Desktop Services—RDS).

Although it’s probably good marketing to attempt to include the older Terminal Services technology under the virtualization umbrella, calling it a virtualization technology is something of a misnomer.

With RDS, a remote console window can be displayed on a network-attached system. That’s about as virtual as it gets.

The remote desktop session is actually interacting with an underlying physical system, and you’re connected to the remote system exactly as if you were using the local display and keyboard.