SUMMARY

Operating systems can be viewed from two viewpoints: resource managers and extended machines. In the resource manager view, the operating system’s job is to manage the different parts of the system efficiently. In the extended machine view, the job of the system is to provide the users with a virtual machine that is more convenient to use than the actual machine.

Operating systems have a long history, starting from the days when they replaced the operator, to modern multiprogramming systems. Highlights include early batch systems, multiprogramming systems, and personal computer systems.

Since operating systems interact closely with the hardware, some knowledge of computer hardware is useful to understanding them. Computers are built up of processors, memories, and I/O devices. These parts are connected by buses.

The basic concepts on which all operating systems are built are processes, memory management, I/O management, the file system, and security. Each of these will be treated in a subsequent chapter.

The heart of any operating system is the set of system calls that it can handle. These tell what the operating system really does. For UNIX, we have looked at four groups of system calls. The first group of system calls relates to process creation and termination. The second group is for reading and writing files. The third group is for directory management. The fourth group contains miscellaneous calls.

Operating systems can be structured in several ways. The most common ones are as a monolithic system, a hierarchy of layers, a virtual machine system, an exokernel, or using the client-server model.