The big idea: The role of an OS breaks down into a set of named functions.
Each one manages a different resource, and the exam expects you to name them and say what each actually does.
All at once, all the time: These run constantly in the background while you use the machine — and must keep running correctly even as programs start, crash and close.
That is what "maintaining system integrity" means.
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Memory management
Scheduling
File system
Device management
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Security
- Checks who is logged in and what they may do
- Refuses a program access it has not been granted
- Keeps the OS's own memory out of reach of programs
Accounting
- Records how much CPU time, memory and storage is used
- Used for billing on shared or cloud systems
- Also how the OS spots a program consuming too much
Graphical user interface
- Draws the windows, menus and pointer
- Turns clicks and keystrokes into messages for programs
- Gives every program the same look and controls
Virtualization
- Lets one machine appear to be several separate ones
- Each virtual machine has its own OS and cannot touch the others
- How one physical server hosts many customers
Networking
- Sends and receives data over the network
- Handles addressing and the rules for the conversation
- So a program just says "fetch this"
System integrity: All nine run while programs start, crash and close around them.
A program that fails must not take the OS with it — which is why the OS keeps its own memory separate and never lets a program reach hardware directly.
How this is tested — you must NAME the function and say what it manages — a name alone is not an answer. It comes up two ways:
Paper 1 Section A
- Describe the functions of an OS, 3-6 marks
- Name the function responsible for a stated job
- Explain how one function protects the system
Paper 1 Section B — case study
- Say which functions matter most to the case study
- Justify it from that organisation's setup
The classic trap: Listing names and stopping. "Memory management, scheduling, security" is a list, not a description. Each name needs a clause: what it manages, and what would go wrong without it.
A shared office computer is used by several staff, each with their own account, running many programs at once. Describe two functions of the operating system that make this possible.
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