Operating systems

An operating system (OS) manages a computer and lets users and applications use its hardware. Its user interface lets people control the computer. A graphical user interface (GUI) uses windows, icons, menus and a pointer; a command-line interface (CLI) accepts typed commands. A GUI can be easier to learn, while a CLI can be quick for an experienced user performing repeated tasks.

For example, Windows' desktop is a GUI; a system administrator might use a CLI to manage files on a server.

The OS manages memory by allocating RAM to programs and moving data between memory and storage; this helps several applications run together (multitasking). It manages peripherals, such as printers, and uses device drivers to communicate with particular devices. It manages users by creating accounts, checking sign-ins and setting access rights. It manages files by naming them, arranging folders, and saving, moving and deleting them.

For example, when a document is printed, the OS and printer driver pass the job to the printer while the user continues editing. The specification does not require the details of memory paging or segmentation.

Opening one program uses almost every job of the OS:

1. You double-click its icon in the user interface.
2. The OS finds the program's file on storage (file management).
3. It loads the program into RAM and allocates it memory (memory management).
4. It shares the processor's time between this program and others that are running (multitasking).
5. It checks that you are allowed to open the files you choose (user management).
6. When you print, it sends the job to the printer through its device driver (peripheral management).