The purpose of the operating system and its main functions: managing memory, processes, peripherals and files, providing a user interface, and managing security.

A Unit 1 operating system question. Award 1 mark for each correctly described function, up to four. Memory management: the OS allocates memory (RAM) to programs and reclaims it when they finish, and uses virtual memory when RAM is full. Process management: the OS schedules and switches between programs so several appear to run at once on a single processor. Peripheral/device management: the OS controls input and output devices using device drivers, handling printing, storage and so on. File management: the OS organises files and folders on storage and handles saving, opening, moving and deleting. Other creditworthy functions are providing a user interface and managing security/user accounts. Markers reward four distinct, correctly described functions. A common error is to list functions without describing them, or to repeat the same function in different words.

A Unit 1 explain question. Process management is the operating system's job of scheduling and controlling the programs (processes) that are running, deciding which one uses the CPU and when (1 mark). On a single processor only one instruction can be executed at a time, so the OS rapidly switches between processes, giving each a small slice of CPU time (1 mark). This makes it appear that several programs are running at the same time, even though the processor is really handling them one after another very quickly (1 mark). Markers reward scheduling, switching between processes and the appearance of multitasking. A common error is to say a single processor truly runs many programs simultaneously, when it switches between them.