Licensing for virtualisation will be dependent on the software vendor of the virtualisation software. However which ever virtualisation software is used, you would still need to be licensed for each instance of a virtualisation you are running. An example of this could be running 20 virtual desktops from a server, where you would still need 20 Operating System licences to run those virtualisations, likewise with application virtualisation, you would need a licence for each virtualisation of the application.
Software is used to transform or "virtualise" the hardware resources of an x86-based computer-including the CPU, RAM, hard disk and network controller-to create a fully functional virtual machine that can run its own operating system and applications just like a "real" computer. Multiple virtual machines share hardware resources without interfering with each other so that you can safely run several operating systems and applications at the same time on a single computer. So Instead of a machine having its own physical hard drive, its hard drive is simply a file residing on the host machines file system. Similarly RAM, software installed on the host gains access to more memory than is physically installed, via the background swapping of data to disk storage.
Server Virtualisation
Server Virtualisation is a process where one or more complete server operating systems and their applications are encapsulated on a host server within a virtualised environment.
Application Virtualisation
Application Virtualisation is a way of centralising the execution and delivery of organisations applications. There has been a move towards this in recent years and although it seems like a backwards step, it has been driven by IT managers who wish to regain control of their IT resources and reduce the inherent support and cost issues associated with desktop computing.
Desktop Virtualisation
Desktop virtualisation is different from application virtualisation in that application virtualisation can deliver a virtualised desktop to users, but it will still be running on the same operating system in the background, meaning that it would be sharing the resources and vulnerabilities of that operating system if it were to fail. Desktop virtualisation however, refers to the delivery of a complete virtual operating system running on a dedicated virtual machine. In order to make the virtual machines manageable a service would be required to automatically allocate virtual desktops to users.
Network Virtualisation
Network virtualisation is a subset of server virtualisation, where once created the virtual servers may be linked using 'virtual switches' created within the same software. These switches may then be used to connect to a physical network or used internally by just the virtual machines. This means that a secure virtual network can be created, as all data communications are only taking place within the virtual environment.
Improved utilisation of physical resources, servers and storage, means that less hardware is required to deliver a given processing capability. This reduces capital expenditure, data-centre space and operating costs.
Virtualisation creates a common layer of control over underlying devices from different manufacturers. Centralised systems management can be performed faster, more easily and with fewer resources.
Managing representations of complete physical systems in software greatly increases the scope and potential of remote administration and deployment.
Physical processor and storage capacity can be increased or re-allocated without disrupting data processing operations.
Virtualisation opens the door to alternative and complimentary techniques for achieving high availability and disaster recovery.
Instances of virtual servers and their applications can be cloned and used as templates to allow agile businesses to deploy software and servers rapidly, anywhere in the world.
Virtualisation essentially lets one computer do the job of multiple computers, by sharing the resources of a single computer across multiple environments. Virtual servers and virtual desktops let you host multiple operating systems and multiple applications locally and in remote locations, freeing you from physical and geographical limitations. In addition to energy savings and lower capital expenses due to more efficient use of your hardware resources, you get high availability of resources, better desktop management, increased security, and improved disaster recovery processes when you build a virtual infrastructure.