rray of Independent Disks (RAID). The advantage of arrays working together as one device is that if a drive is on the verge of failing, its contents are automatically moved to a functioning drive in the array. The small size of hard drives has made it possible for organizations to store enor- mous amounts of data in less space. In data centers, switches connect storage systems to computing systems (applications). In large organizations, a specialized, centralized staff manages the storage. These SANs communicate with physical servers that run operating systems, which in turn run applications. Virtualization is implemented to decrease server sprawl. (See Chapter 1 for an explanation of virtualization.) In virtualized host physical servers, operating systems are configured to act like SANs that store and run applications rather than databases. A piece of software called a hypervisor allocates server memory, disk space, cen- tral processors, and network connections to the applications running on the physical computer. In data centers with only one physical server running applications on virtual machines, the physical server itself is referred to as the SAN. Switches connected to virtualized physical servers manage communications between the following: Applications on physical servers and users that access them Physical servers in the data center Applications on virtual machines and software applications used to manage and troubleshoot problems within data centers Switches also run security operations to protect applications from attacks by unau- thorized users. There are more switches than physical servers because of the high fre- quency of communications between physical servers and other devices. In data communications parlance, a port is an interface into which a cable is plugged for linking a computer to another device (a laptop to a display), or to link devices to networks. Next-Generation Data Centers: Virtualization and Gigabit Speeds Storage Capacity on Commodity Servers: A Lower- Cost Approach An alternativ