Application architectures are of the following types: Single-tier Two-tier Three-tier N-tier In the case of a single-tier architecture, a single executable file handles all functions related to the user, business, and data service layers. Such an application is also called a monolithic application.Examples of single-tier architecture can be found in some of the very early COBOL programs performing extremely mission-critical operations. The two-tier architecture divides an application into the following components: Client Server The client implements the user interface. The server stores the data.The communication between a Web browser and a Web server is an example of client server architecture.In the two-tier system, the actual processing of data takes place on the server. Therefore, the data has to be transported over the network. This leads to increased network stress. To overcome these problems, there was a shift from the two-tiered to the three-tiered systems. In the three-tiered system, there is a clear separation of user-interface-control and data presentation from application-logic. Therefore, more clients are able to access a wide variety of server applications. This leads to quicker development through the reuse of pre-built business-logic components and a shorter test phase because the server-components have already been tested The N-tier Architecture (Contd.) Client interface- The client interface layer represents the end-user presentation, such as the windows forms. Business tier- The business layer is the most important part of the n-tiered architecture. It contains the business rules and data manipulation/transformation logic. Data access tier- The data access layer is a reusable interface to the database. It contains the generic methods used to interface with the data. Data tier- The data layer deals with storage and retrieval of information. Basically, the data tier consists of the database management systems