Components of an Operating System

Components of an Operating System
In order to perform the actions requested by the computer’s users, an operating system must be able to communicate with those users. The portion of an operating system that handles this communication is often called the user interface. Older user interfaces, called shells, communicated with users through textual messages using a keyboard and monitor screen. More modern systems perform this task by means of a graphical user interface (GUI) in which objects to be manipulated, such as files and programs, are represented pictorially on the display as icons. These systems allow users to issue commands by using one of several common input devices. For example, a computer mouse, with one or more buttons, can be used to click or drag icons on the screen. In place of a mouse, special-purpose pointing devices or styluses are often used by graphic artists or on several types of handheld devices.

More recently, advances in fine-grained touch screens allow users to manipulate icons directly with their fingers. Whereas today’s GUIs use two dimensional image projection systems, three-dimensional interfaces that allow human users to communicate with computers by means of 3D projection systems, tactile sensory devices, and surround sound audio reproduction systems are subjects of current research.

Although an operating system’s user interface plays an important role in establishing a machine’s functionality, this framework merely acts as an intermediary between the computer’s user and the real heart of the operating system. This distinction between the user interface and the internal parts of the operating system is emphasized by the fact that some operating systems allow a user to select among different interfaces to obtain the most comfortable interaction for that particular user.

Users of the UNIX operating system, for example, can select among a variety of shells including the Bourne shell, the C shell, and the Korn shell, as well as a GUI called X11. The earliest versions of Microsoft Windows were a GUI application program that could be loaded from the MS-DOS operating system’s command shell. The DOS cmd.exe shell can still be found as a utility program in the latest versions of Windows, although this interface is almost never required by casual users.

Similarly, Apple’s OS X retains a Terminal utility shell that hearkens back to that system’s UNIX ancestors. An important component within today’s GUI shells is the window manager, which allocates blocks of space on the screen, called windows, and keeps track of which application is associated with each window. In contrast to an operating system’s user interface, the internal part of an operating system is called the kernel. An operating system’s kernel contains those software components that perform the very basic functions required by the computer installation. One such unit is the file manager, whose job is to coordinate the use of the machine’s mass storage facilities.

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