Client-server architectures are divided into various multi-tier architectures, the one-tier architecture, the two-tier architecture and the three-tier architecture. The two-tier architecture consists of two important components: the intelligent client, a fat client, which forms one tier with the user interface. The second tier is formed by the server in the backend, where the databases are stored.
In the two-tier concept, the client provides the graphical user interface into which the user enters his input. The client itself has its own operating system and processes its own application programs. It only accesses the databases of the server to retrieve stored data and to store results. By command input of the client to the server this can print files or documents. Between the two tiers, the client and the data server, a direct connection, a local network or the Internet can provide for communication.