Microsoft Windows DNA is based on a distributed system architecture. Distributed systems contain components on more than one computer. An Internet-based system is a typical example of a distributed system, as it contains an application running on a client computer (usually a browser-based application) and one or more applications running on a Web server. The Web server can also communicate to other servers. In this tutorial, we'll focus on building Windows DNA systems, but the discussion is equally applicable to other distributed systems.
One of the primary goals of distributed systems is to be highly scalable. A highly scalable system can easily expand from thousands of users to tens of thousands of users. Over the last two decades, we've witnessed a steady evolution from Windows systems that can handle a few hundred users, such as a department-size application, to systems that can handle tens of thousands of users, such as an Internet application. This tutorial will demonstrate how a distributed system can be highly scalable.
Because distributed systems contain a variety of components located on several computers, these systems are usually extremely complex. Without a framework such as the one provided by Windows DNA, designing and building such a system would be impossible. The Windows DNA architecture provides two models for designing and building large, complex distributed systems: the logical three-tier model and the physical three-tier model. The logical three-tier model is used to define and design the components of the system. The physical three-tier model is used to specify the placement of these components within the distributed system. Let's begin by looking at the logical three-tier model.