Global view

Purpose of an Operating System

Support (base) program executed by the computational system.

Gives life to the computer (hardware), providing an abstract interaction environment.

Acts as an interface between the machine and the application programs.

Manages and schedules memory, processors, and other system devices.

Objectives of an Operating System:

• Convenience in the way the computer is used.

• Efficiency in the use of computer resources.

• Ability to evolve to permit the development of new system functions.

Operating system as an extended machine

This is an outer-inner or user view.

The operating system provides an abstract view of the underlying computational system that frees programmers of the hardware details.

• A functional model of the computational system (a virtual machine), that is simple to understand and program.

• The interface with the hardware is a uniform programming environment, defined as a set of system calls, that allows the portability of applications among structurally different computational systems.

Some typical functionalities of the operating system:

• Establishment of a user interaction environment.

• Provision of facilities for the development, testing, and validation of programs.

• Provision of mechanisms for the controlled execution of programs, including their intercommunication and synchronization.

• Dissociation of the program’s address space from the constraints imposed by the size of the main memory.

• Control access to the system as a whole and to specific system resources, protecting against unauthorized access and resolving conflicts.

• Organization of secondary memory in file systems and control access to files.

• Definition of a general model for access to input/output devices, regardless of their specific characteristics.

• Detection of error situations and establishment of appropriate response.

Operating system as a resource manager

This is the inner-outer or computational system view.

A computational system is a system composed of a set of resources (processor(s), main memory, secondary memory, I/O device controllers) targeting the processing and storage of information.

The operating system is the program that manages the computer system, making the controlled and orderly allocation of its different resources to the programs that compete for them.

• Resource usage is multiplexed in space and time.

Aims at maximizing the performance of the computational system, ensuring the most efficient use of existing resources.