3.2.1 Operating systems

What Is an Operating System?

An operating system (OS) is software that manages a computer's hardware and provides a platform on which application software can run. Without an OS, application programs would each need to include their own routines to control hardware — an impractical and insecure approach. The OS sits between the hardware and user applications, acting as an intermediary.

Common examples: Windows, macOS, Linux, Android, iOS.

Four Key Functions

File management is the OS function responsible for organising, storing and retrieving files on secondary storage. This includes:

  • Maintaining a hierarchical directory (folder) structure
  • Tracking where files are physically stored on the disc
  • Handling file operations: create, read, write, rename, delete, move
  • Managing file permissions — controlling which users can read, write or execute a file
  • Handling fragmentation — keeping track of files split across multiple disc locations

Without file management, every application would need to manage disc access directly, leading to conflicts and data loss.

Process management controls how the CPU's time is shared among multiple running programs. A modern computer runs many processes simultaneously (browser, music player, OS services). The CPU can typically only execute one instruction at a time, so the OS schedules processes — allocating CPU time in small slices to create the illusion of parallel execution.

  • The scheduler decides which process runs next and for how long
  • Processes can be in running, ready or waiting states
  • The OS handles switching between processes without data loss
  • It allocates RAM to processes and ensures one process cannot access another's memory space

Peripheral management (also called device management) controls the interaction between the CPU and hardware peripherals such as keyboards, mice, printers, monitors and network cards.

  • Each peripheral communicates with the OS through a device driver — software that translates generic OS commands into the specific instructions for that hardware
  • The OS manages the queue of requests to peripherals (e.g. multiple print jobs)
  • It handles interrupt signals sent by devices to the CPU (e.g. "a key was pressed")
  • Plug and play: the OS detects newly connected devices and loads appropriate drivers

User management controls access to the computer system by individuals. This includes:

  • Creating and managing user accounts — each user has a username and password
  • Assigning access rights and permissions — different users can access different files and resources
  • Maintaining audit trails — logs of user activity for security monitoring
  • Supporting multi-user systems where many users share the same machine or server
  • Enforcing security policies — e.g. account lockout after failed login attempts

 Key Takeaways

  • The OS manages hardware and provides services to application programs.
  • File management: organises and controls access to files on storage.
  • Process management: schedules CPU time among multiple running programs.
  • Peripheral management: controls communication with hardware devices via drivers.
  • User management: controls who can access the system and what they can do.