1.3 Operating systems

Basic concepts

An operating system (OS) is the software that manages the sharing of the resources of a computer and provides programmers with an interface used to access those resources. An operating system processes system data and user input, and responds by allocating and managing tasks and internal system resources as a service to users and programs of the system. At the foundation of all system software, an operating system performs basic tasks such as controlling and allocating memory, prioritizing system requests, controlling input and output devices, facilitating networking and managing file systems. Most operating systems come with an application that provides a user interface for managing the operating system, such as a command line interpreter or graphical user interface. The operating system forms a platform for other system software and for application software.

The most commonly-used contemporary desktop operating system is Microsoft Windows, with Mac OS X also being well-known. Linux and the BSD are popular Unix-like systems.

The operating system is the first thing loaded onto the computer -- without the operating system, a computer is useless. In detail, important services that an operating system provides are:

• Create Interface between you and your computer
• Manage the file system includes directories, folders, files

• Has a set of commands that allow for manipulation of the file system: sort, delete, copy, etc.
• Perform input and output on a variety of devices
• Allocate Resources
• Manage the running systems

Categorization of operating systems

All desktop and laptop computers have operating systems. Operating systems are categorized based on the types of computers they control and the sort of applications they support.

• Single-user, single task
• Single-user, multi-tasking
• Multi-user
• Real-time operating system

File

A computer file is a block of arbitrary information, or resource for storing information, which is available to a computer program and is usually based on some kind of durable storage. A file is durable in the sense that it remains available for programs to use after the current program has finished. Computer files can be considered as the modern counterpart of paper documents which traditionally were kept in offices' and libraries' files, which are the source of the term.

A filename is a special kind of string used to uniquely identify a file stored on the file system of a computer. Depending on the operating system, such a name may also identify a directory. Different operating systems impose different restrictions regarding length and allowed characters on filenames.

Many operating systems, including MS-DOS, Microsoft Windows, allow a filename extension that consists of one or more characters following the last period in the filename, thus dividing the filename into two parts: the base name (the primary filename) and the extension (usually indicating the file type associated with a certain file format). The base name and the extension are separated by a dot.