Operating Systems

Operating system (OS) software is a set of programs that manage computer hardware resources and facilitate the use of application programs. Examples of modern operating systems are Linux, Mac OS X, Microsoft Windows, iOS, and Android.

The central component of an operating system is the kernel; this is the core software in an operating system that performs the functions listed below. Modern operating systems also have device drivers, as well as a selection of tools or utility programs that are used to manage and monitor the computer.

The activities carried out by the kernel typically include:

Process management. A running computer operating system typically has several programs running at once. The kernel controls the initiation, execution, and termination of these programs, as well as the allocation of hardware components (such as CPUs, memory, and peripherals) between the running programs.

Memory management. The kernel allocates memory to itself as well as to processes that are running. The kernel responds to processes that request more (or less) memory. Programs are permitted to use only the memory allocated to them; the kernel enforces this restriction.

Interrupts. An interrupt is a signal sent to the kernel that directs the kernel to temporarily suspend processing in order to take care of something else. Typically an interrupt comes from one of the computer’s hardware components when some event requires attention from the operating system.

Hardware resource management. The kernel manages each process’s access to the computer’s hardware, including memory, hard disks, network adaptors, and bus adaptors (such as USB and FireWire).

Another important part of the OS is its device drivers. These are programs used to permit interaction between the kernel and specific hardware devices that are connected to the computer.

A vital part of the OS is the user interface. This is the part of the OS that we lowly humans use to communicate with the computer. The two primary types of user interfaces are

Command line. The command line is simple interface controlled by a keyboard. The computer’s user types in a command, and the computer responds. OSs that use a command-line interface include Microsoft DOS, and older version of UNIX.

Graphical. This interface divides the screen into “windows”or “panes,” typically controlled by a pointing device (such as a mouse or touchpad) and perhaps also a keyboard. OSs that use a graphical interface include Linux, Mac OS, Android, and Microsoft Windows.

Operating systems carry out many security functions on a computer, including

Authentication: Before any local or remote user may access any programs or data, the OS needs to know who is performing the access request. The OS requires that the user identify him or herself, typically by entering a userid and password.

Access control: Most OSs control which users are permitted to access resources on the system, such as a printer or scanner.

Process isolation: The OS restricts processes by forbidding any process from accessing or modifying memory allocated to any other process. This prevents any process from tampering with other processes.

Network communication: The OS includes basic network protocols to facilitate communication to other computers.

Filesystem access: The OS restricts access to files and directories in file systems, basing access on permission labels affixed to each file and directory. Only authorized processes may access specific files. This is the mechanism used to restrict users’ access to files on workstations and servers.

Operating systems use these controls not only to protect processes and resources, but also to protect themselves. A good OS is resistant to many kinds of attacks, which in turn helps to protect information stored in the system.