What is Modularity?
Modularity is the encapsulation of sub-system functionality into "black box" components (modules) that are joined to other system components through well defined interfaces. Many exchangeable modules are combined to form the product or system. Desired functionality of the product (or modular system) is achieved through design rules, consisting of the system architecture, the functional requirements for each module, and the standard interfaces joining the modules.

History
Modularity and architecture are common practices in software development, databases, information systems, micro-electronics and electronic product design. These industries were not always modular. Pioneering thinkers brought the principles of modularity to bear on the complex products and processes, and a revolution was begun. Today, we take for granted the low costs, high reliability, and fast development times that a modular approach in these industries provides.

Defining Modular Architecture
Initially defining the modularity can be quite challenging. A system built of modules must be designed to achieve the company business objectives. Modules combined with optimal architecture produce the operational flexibility needed to support future business decisions.

Modularity Is Strategic
Modularity is strategic in both product design and in manufacturing. Choices made during modularization can often be limiting. A sub-optimal modular system can be difficult to upgrade. The manufacturing process may still have a fixed capacity or a fixed process sequence. The product may not be a platform yet, thus limiting variants. For modularity to be beneficial, the requirements of the business must be well defined. The product design becomes a platform that launches many different products. The manufacturing system becomes a modular platform that enables future new product introductions.

It looks modular, But…
is lacking architecture. Systems that appear modular often do not have the necessary architecture to provide the agility that operations management would expect from a modular system.

has invisible constraints. It seems incredible, but it is quite possible to "hard tool" a modular machine using poorly designed control system software that is difficult to upgrade and maintain.