Operating Systems

Overview

An operating system is a system software that manages computer hardware and software resources, and provides common services for computer programs. According to Dusseau, an operating system is responsible for:

1. Virtualization. The OS takes a physical resource and transforms it into a more general, powerful, and easy to use virtual form of itself.
2. Concurrency. The OS provides the necessary primitives for correctly executing many concurrently executing threads.
3. Persistence. The OS stores data in a durable way by managing various I/O devices. It also uses durable memory to share information between different processes.

The kernel of an operating system refers to the memory-resident part of the OS.

Policies

A policy is an algorithm for making some kind of decision within the OS. For example, a scheduling policy is used to decide which processes should run when the current one is suspended.

A mechanism is a low-level method or protocol that implements some needed functionality.