systems, with each operating system running multiple applications. Each operating system running multiple applications is a virtual machine. This reduction in the num- ber of servers required to support vast numbers of applications made virtualization a key building block for cloud computing. Technical advances have enabled virtualization to make it possible for large enter- prises and cloud computing providers to consolidate servers. Supporting more than one operating system on a single physical server requires large amounts of processing power. However, with the development of powerful multi-core processors, parallel- computing streams can perform multiple computer instructions simultaneously. As of this writing, multi-core processors can contain up to eight core processors. Virtualization host operating software from companies such as VMware, Inc. (EMC is the majority owner) and Microsoft allocate and manage computer resources Computing and Enabling Technologies such as memory, hard-disk capacity, and computer processing between the operating systems and applications on a server. Virtualization management software simplifies data center operations by providing the ability to allocate more resources in a data center from a single interface. Scalability and Energy Savings Carriers, ISPs, enterprises, and developers adopt virtualization as a way to save on energy, computer memory, staffing, and hardware costs. Installing applications on multiple virtual computers on each physical server decreases the number of physical servers required. It also ensures that there is less wasted capacity than on physical serv- ers used for a single application, often using only 10 percent of the physical server's capacity. This makes data centers more scalable. Applications can be installed more easily, without adding extra hardware. Rather, a new virtual machine can be added to a physical computer that has spare capacity until the physical server is at between 70 percent and 80 percent of capacity. In addition, having fewer compu