Virtualization is a method of running multiple independent operating systems on a single physical Server. It is a way of maximizing physical resources to maximize the investment in hardware.  Number of virtual machines in a Server is depending upon the resource availability of the parent server. Virtualization is the perfect solution for applications that are meant for small/medium scale usage. Server virtualization have a meager role in green it Projects, Energy consumption is a critical issue for IT organizations today,  virtualization help you to save more rack space, reduce the power consumption, data center temperature and rack space utilization. Server consolidation using virtualization is a good idea for disaster recovery and for development servers.

Following are the popular applications using for virtualization

Microsoft Virtual Server , Vmware ,  Sun xVM,  Xen