The operating system

The operating system (OS) is a resource manager. It manages all the resources of the computer: the CPU, RAM, disk, network and input-output devices. It controls the running applications and the device drivers, and looks after security and the different users.

It has two main objectives:

• to provide services for building and running programs: loading them into memory, giving them time on the CPU, and deciding the order in which they run;
• to provide a user interface, through which people use the computer.

Types of user interface:

• Command-based: the user types commands, using the keyboard (MS-DOS, Unix).
• Graphical user interface (GUI): icons, menus and windows, used with a mouse (Windows, Ubuntu, macOS). Click the camera icon, and the camera app opens.
• Touch-based: tap and swipe on the screen (Android, iOS).
• Voice-based: speak a command, as in 'Hey Siri, play this song' or 'OK Google' (Siri, Google Assistant, Cortana).
• Gesture-based: control by movements of the hand or body.

The OS manages four main areas:

• Process management: a program (or task) in execution is called a process. Many processes may want the CPU at once; the OS decides how to share the CPU among them.
• Memory management: giving main memory to processes when they start, and freeing it when they finish.
• File management: creating, updating, deleting and protecting files in secondary memory, so that one user's files are safe from others.
• Device management: working with device drivers, configuring devices and restricting access to them.