Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. In systems engineering, modular design - or "modularity in design" - is an approach that subdivides a system into smaller parts (modules) that can be independently created and then used in different systems to drive multiple functionalities. A modular system can be characterized by the following: "Functional partitioning into discrete scalable, reusable modules consisting of isolated, self-contained functional elements; Rigorous use of well-defined modular interfaces, including object-oriented descriptions of module functionality; Ease of change to achieve technology transparency and, to the extent possible, make use of industry standards for key interfaces." Besides reduction in cost (due to lesser customization, and less learning time), and flexibility in design, modularity offers other benefits such as augmentation (adding new solution by merely plugging in a new module), and exclusion. Examples of modular systems are cars, computers and high rise buildings. Earlier examples include looms, railroad signaling systems, telephone exchanges, pipe organs and electric power distribution systems.