Object-Based Computing

Software objects are a combination of computer instructions and data that models the behavior of things, real or imagined, in the world. Objects are composed of the following elements.

• Attributes, in the form of program variables, which collectively define the object's state
• Behavior, in the form of code modules or methods that can modify those attributes
• An identity that distinguishes one object from all others

Objects interact with each other by passing messages back and forth. The sending object is known as the client and the receiving object is known as the server. The client requests, and the server responds. In the course of conversation, the client and server roles often alternate between objects. Windows NT is not an object-oriented system in the strictest sense, but it does use objects to represent internal system resources.

Windows NT uses an object metaphor that is pervasive throughout the architecture of the system. When viewed using Windows NT, all of the following appear as ordinary objects.

• Devices, such as printers, tape drives, keyboards, and terminal screens
• Processes and threads
• Shared memory segments
• Access rights