8.1 Security

We say that a system is secure if its resources are used and accessed as intended under all circumstances. Security, must consider both the computer system and the environment such as people, buildings, businesses, valuable objects, and threats within which the system is used. In multiuser systems, several users store their data and programs in the system. The system data is also stored there, and is shared by all users. Because many users use a multiuser system, simultaneously, there is a critical need to protect files from unauthorized use. There are three main security principles for any type of security control: Availability, Integrity, and Confidentiality.
By access controls we mean the security features that control how users and systems communicate and interact with one another. A system secured for one environment may be unsuitable for another, and vice versa. Operating system designers must define what security means for their particular needs.