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In this chapter, we describe, comment, and motivate discussions upon basic concepts and principles of component models and component services. We argue that component systems have been used at a coarse-grained level for decades. Discussions and disagreements concerning the term component have appeared because industry and academia have tried to develop technologies for smaller, fine-grained components.

Early component systems Operating systems are among the first successful component systems (Szyperski 1997). We expect readers to be familiar with at least one operating system; and, thus, we will use operating systems to illustrate the basic ideas behind component models and component model implementations. Operating systems provide an execution environment for software applications. In particular, operating systems present an abstraction of the underlying hardware to applications and regulate their shared access to various resources. They also provide basic services, such as memory management, file management, interprocess communication, process synchronization, and security. Without operating systems, each individual application would have to implement such general functionality. The availability of a wide range of services simplifies application development. Naturally, interfaces have to be defined to let applications use these services. These interfaces are called application programming interfaces (APIs).