An operating system handles input/output control, file maintenance, the software/hardware interface, memory allocation, constructs the user interface, controls software execution, and organises security and virtual memory. Operating systems can be single user, multi-user, or multi-processing. Multi-tasking allows one client to run multiple programs at once while multi-threading runs different parts of a single program simultaneously. Utility software performs specific hidden tasks like backups or antivirus protection, unlike applications which users choose for their needs.

1. 6 Further System Fundamentals (HL) ‏ 6.3 Operating Systems and Utility Software 6.3.1 Operating Systems

2. Definition (review) A collection of system software that: Handles input/output (I/O) control Performs file maintenance Handles the software/hardware interface Manages memory allocation

3. Definition (review) Constructs the user interface Controls software execution Organises security (log in, permissions, etc.) Organises virtual memory.

4. Definitions Single user : only one client can use the processor at a time e.g. DOS Multi-user : the processor can share its time between many clients e.g. Windows Multi-processing : one computer running on several processors e.g. dual core or distributed computing.

5. Definitions Multi-tasking : one client can run more than one program at a time e.g. email, spreadsheet, browser... Multi-threading : many parts of a single program can all run at the same time e.g. during a game

6. Utility software Performs a specific task that is usually hidden from the user Example: automatic backup, anti-virus As distinct from an application which the user chooses according to their needs.