Application models do not change very often, but when they do, they create many opportunities.

I had a front row seat at Microsoft to watch the first two application model transitions. Early mainframe and minicomputer systems were monolithic, with data storage, application code, and terminal services all in one box. When the microprocessor and ethernet networks emerged during the 1980s, they enabled lower-cost computers to work together and communicate over local area networks. PC’s and Unix workstations began to connect to servers, leveraging a new, multi-machine, client-server programming model for business applications. Client-server applications emerged with a graphical user interface coupled to a backend SQL Database (frequently Oracle or SQL Server).

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Client-server applications were built very differently than monolithic applications, with the presentation code running on the client computer and business logic on the server, typically encapsulated within SQL stored procedures:

I watched the client-server journey begin over 30 years ago, while working on my first Microsoft product, the Ashton Tate/Microsoft OS/2 SQL Server.

Client-server applications flourished for only a brief period but they created a new generation of easy-to-use, graphical applications that delivered computing to hundreds of thousands of small businesses for the first time. The combination of Visual Basic client applications calling SQL Server stored procedures built the Microsoft server business and created an entire industry of software vendors and value-added resellers. While client-server has been a legacy approach for over 20 years, many businesses continue to run updated versions of these same client-server applications.

Client-server became legacy because of the Internet and the Web. Client-server applications were built for local area networks using chatty, proprietary protocols that worked in a local-area network but were inappropriate for the long distances required by the Internet.

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