What is an Application Server?

An application server is a software platform designed to simplify building, deploying, running, and maintaining large-scale, multiuser applications, such as payroll systems, expense report tracking, and sales force automation. They do so by reducing the amount of custom infrastructure code that developers must write, freeing them to focus on the custom code required for their specific business problem.

The most widely used architecture for developing large-scale business applications is a component-based, three-tier model. The three-tier application model divides an application into three logical partitions, or tiers: a user interface (UI) tier for client interactions, a middle tier for business logic, and a data tier for data storage. The use of components to build the tiers facilitates code reuse—rather than each application requiring its own code to manage incoming requests, for example, a single queuing component can perform this task for multiple applications—which makes the development process easier to manage. (For more information on component-based, three-tier applications, see the sidebar “Why Use Components and Three Tiers?“.)