Deployment diagrams represent the phyical relationships among software and hardware components as realized in a running system.This type of diagram is useful for showing how components and objects move about in distributed systems

Deployment diagrams depict the physical resources in a system including nodes, components, and connections.

Components in a component diagram are contained in the deployment diagram elements. while components provide the application functionality, the deployment diagram elements provide the necessary environment for the components to execute in. 

The basic deployment diagram element is the node. The node represents the environment in which a component or a set of components execute. This means that a node in a deployment diagram can represent a multitude of things—physical hardware such as a server machine, a system software like an operating system, or even application infrastructure software like a Web server, application server, database server, and so forth. The different nodes in the deployment diagram can be interconnected to represent interdependencies, thus providing a deployment diagram that is easy to comprehend and provides the complete deployment environment of a system.

Following figure shows a sample Deployment diagram.

Usage of deployment diagrams can be described as follows:

1.To model the hardware topology of a system.

2.To model embedded system.

3.To model hardware details for a client/server system.

4.To model hardware details of a distributed application.

5.Forward and reverse engineering