Operating systems

An operating system is system software that acts as an intermediary between user programmes and computer hardware. Its core task is resource management: it allocates CPU time, memory, files, devices and network access while hiding low-level hardware details behind controlled interfaces. Common services include programme execution, input-output handling, file and directory management, communication between processes, error detection, accounting, protection and security. The kernel is the privileged core that controls hardware; the shell or graphical desktop is the user-facing layer for commands and interaction.

Operating systems are classified by use and behaviour. A batch OS runs jobs without continuous user interaction. A time-sharing OS gives many users or processes the impression of simultaneous service by rapidly switching CPU time. A real-time OS responds within strict deadlines and may be hard real-time or soft real-time. Distributed systems coordinate multiple networked computers; embedded systems run inside devices such as routers, printers and controllers. Mobile operating systems add power management, touch input, sensors and application sandboxing. In an RSSB computer lab, the same theory explains Windows desktops, Linux servers and Android tablets used for learning or attendance.

Exam focus: an OS is not just a user interface; it is the manager and protector of all major hardware resources.