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One final consideration for this chapter is the concept of virtualization. Throughout this chapter, I use the term server to refer both to an operating system that provides services such as file sharing or directory services, as well as to the hardware on which that operating system runs. However, in many (if not most) modern network environments, a single physical computer system is used to run more than one virtual machine (VM). A VM is a simulation of an actual computer system. This concept is called virtualization. When virtualization is used, a single physical server computer actually runs more than one virtual server.

Virtualization is the reason that server computer hardware often has such high performance specifications, such as dual processors with multiple cores each and a large amount of RAM (256GB or more). In most environments, no single server really needs that much capacity. But when a single physical computer is responsible for running multiple virtual servers, the physical server must have sufficient capacity to run all its virtual servers.

If this concept seems confusing at first, don’t sweat it. You’ll learn more about virtualization in Book 3, Chapter 4, and in Book 5.