Nearly all software systems today are designed and built to be modular; that is, they consist of separate components or modules that are connected together to form the larger system. The beauty of modular architecture is that it is possible replace or add any one component (module) without affecting the rest of the system. The opposite of a modular architecture is an integrated architecture, in which no clear divisions exist between components. The integrated architecture is not preferred for larger projects requiring more than a very small number of developers, because it requires every developer to have a comprehensive view of the total system, which is impossible for large systems and many developers.

Although the basic principles of modular design can apply to both hardware and software, modular software design in particular is based on a design strategy in which software is composed of relatively small...