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Practical UNIX & Internet Security

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1.2 What Is an Operating System?

For most people, a computer is a tool for solving problems. When running a word processor, a computer becomes a machine for arranging words and ideas. With a spreadsheet, the computer is a financial planning machine, one that is vastly more powerful than a pocket calculator. Connected to an electronic network, a computer becomes part of a powerful communications system.

At the heart of every computer is a master set of programs called the operating system. This is the software that controls the computer's input/output systems such as keyboards and disk drives, and that loads and runs other programs. The operating system is also a set of mechanisms and policies that help define controlled sharing of system resources.

Along with the operating system is a large set of standard utility programs for performing common functions such as copying files and listing the contents of directories. Although these programs are not technically part of the operating system, they can have a dramatic impact on a computer system's security.

All of UNIX can be divided into three parts:

From the point of view of UNIX security, these three parts interact with a fourth entity:

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1.1 What Is Computer Security?Book Index1.3 History of UNIX