Page 15 - DCAP103_Principle of operating system

Principles of Operating Systems

Notes
Figure 1.3: Abstract View of the Components of a Computer System

The hardware-the central processing unit (CPU), the memory, and the input/output (110) devices-
provides the basic computing resources. The application programs-such as word processors,
spreadsheets, compilers, and web browsers—define the ways in which these resources are used
to solve the computing problems of the users. The operating system controls and coordinates
the use of the hardware among the various application programs for the various users. The
components of a computer system are its hardware, software, and data.
The operating system provides the means for the proper use of these resources in the operation
of the computer system. Operating systems can be explored from two viewpoints: the user and
the system.

An operating system is similar to a government. Like a government, it
performs no useful function by itself. It simply provides an environment
within which other programs can do useful work.

1.4 Supervisor and User Mode

In computer terms, supervisor mode is a hardware-mediated flag which can be changed by
code running in system-level software. System-level tasks or threads will have this flag set
while they are running, whereas user-space applications will not. This flag determines whether

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