Application server history
Applications historically were stored on mainframe computers and delivered to computer terminals. Only large institutions — such as governments, banks, and large corporations — could afford the facilities, equipment, and staff to support mainframes. The 1960's saw the introduction of the mini computer. Mini computers are much smaller, less powerful, and much less expensive than mainframe computers. However, computer terminals were still used to interact with the application.
Following the introduction of the personal computer in the 1980s, and more specifically the graphical user interface in the 1990s, the client-server computing paradigm was developed. In the client-server architecture, applications are stored on the server computer and the personal computer serves as the user interface. In this architecture the user interface is a computer program running separately from the database server program. Whereas this freed the database server from managing both the data and the user interface, it required the system administrator to update the client software on each personal computer individually when changes were made.
Following the introduction of the Internet in the mid-1990s, the application server paradigm was developed. Application servers are a throwback to mainframe computing in that both the application and user interface are stored on the server computer. The difference, though, is the client is now a thin client or a personal computer running a browser. The server sends both the instructions for the user interface along with the data to the client. The client then uses its own processing power to format the data using the instructions received. Application servers store the user interface instructions in interface modules which are then assigned to database datatypes. When a database element of a particular database datatype is requested, the application server sends the module's instructions along with the requested data to the client.