An operating system (OS) is system software that manages computer hardware and software resources and provides common services for application programs. Without an OS, application software cannot run — it acts as an intermediary between the user, applications, and hardware.
Examples: Windows 11, macOS, Linux, Android, iOS, ChromeOS
Functions of an Operating System
OCR J277 requires you to know the following OS functions in detail:
1. Process Management
The OS manages all processes (programs) running on the CPU. This includes:
Multitasking / time-slicing: The CPU switches rapidly between processes, giving the illusion they run simultaneously
Process scheduling: Determines which process gets CPU time next (e.g. round-robin, priority scheduling)
Process states: Running, ready (waiting for CPU), blocked (waiting for I/O)
2. Memory Management
The OS allocates RAM to processes and ensures they don't interfere with each other:
Virtual memory: Uses secondary storage (HDD/SSD) as an extension of RAM when RAM is full. Pages of memory are swapped between RAM and disk (paging/swapping)
Memory protection: Prevents one process from accessing another's memory space
Memory allocation: Tracks which parts of RAM are in use and which are free
3. File Management
The OS provides a file system to organise data on secondary storage:
Creates, reads, updates, and deletes files
Organises files into folders/directories (hierarchical file system)
Controls access permissions (who can read/write/execute files)
Manages different file systems (NTFS, FAT32, ext4)
Tracks file locations on disk using an index/allocation table
4. Device Management (I/O Management)
The OS communicates with hardware devices through device drivers:
Device drivers translate OS commands into device-specific instructions
The OS provides a consistent interface so applications don't need device-specific code
Text-based commands typed by user. Faster for experts. Lower resource usage.
Linux terminal, Windows CMD
Touch interface
Tap, swipe, pinch gestures on touchscreens.
Android, iOS
6. Security Management
User authentication (usernames, passwords, biometrics)
Access control — permissions (read, write, execute) for files and resources
Firewall management
Audit logs — records of user and system activity
Virtual Memory
Virtual memory is a memory management technique where secondary storage is used to supplement RAM. When RAM is full, the OS moves the least-used pages of memory to disk (the swap file / page file). The CPU can still access these as if they were in RAM, but accessing disk is much slower — this causes thrashing if overused (constant swapping slows the system dramatically).
Multi-tasking
Modern OSs allow multiple processes to appear to run simultaneously. The CPU rapidly switches between processes using time slicing — each process gets a short time slot (quantum). The OS scheduler decides the order using algorithms such as:
Round-robin: Each process gets equal time in turn
Priority scheduling: Higher-priority processes run first
First Come First Served (FCFS): Processes run in the order they arrived
Types of Operating System
Type
Description
Example
Multi-user
Multiple users can use the system simultaneously
Linux server, mainframe
Multi-tasking
Multiple processes run concurrently
Windows, macOS
Real-time
Guarantees response within defined time constraints. Used in safety-critical systems
Aircraft control, pacemakers
Distributed
Manages resources across a network of computers
Google's data centres
Embedded
Minimal OS built into a specific device
Smart TV, microwave controller
Exam tip: Learn the 6 OS functions — these are examined directly ("State three functions of an OS"). For virtual memory: always mention that it uses secondary storage as an extension of RAM, and that it is slower. For multi-tasking: explain that the CPU time-slices between processes rather than running them literally simultaneously. For interfaces: know advantages and disadvantages of GUI vs CLI.
⚠️ Common Mistakes
Saying the CPU runs multiple programs at the same time — in single-core systems, the CPU rapidly switches between processes (time-slicing)
Confusing virtual memory with RAM — virtual memory uses secondary storage (HDD/SSD), which is much slower than RAM
Forgetting device drivers — these translate OS commands to device-specific instructions and are essential for I/O management
Saying CLI is "worse" than GUI — CLI is faster for experts and uses fewer resources; GUI is better for novice users
Listing "internet" or "antivirus" as OS functions — these are applications or services, not core OS functions
✅ Notes completed!
▶
Video coming soon
Click slide or press arrow keys to navigate
Worksheet — 1.6.1a Operating Systems
8 questions · 23 marks
Q1What is an operating system? State its main purpose.[2]
✅ Mark scheme
An operating system is system software [1] that manages computer hardware and software resources, and provides a platform for application software to run on [1].
Q2State four functions of an operating system.[4]
✅ Mark scheme
Any four: Process management [1]; Memory management [1]; File management [1]; Device/I/O management [1]; User interface [1]; Security management [1].
Q3Explain what virtual memory is and why it is needed.[3]
✅ Mark scheme
Virtual memory uses secondary storage (HDD/SSD) as an extension of RAM [1]; it is needed when RAM is full — the OS moves the least-used pages to disk to free up RAM for active processes [1]; it is slower than RAM so overuse causes the computer to run slowly [1].
Q4What is a device driver? Why are device drivers necessary?[2]
✅ Mark scheme
A device driver is software that allows the operating system to communicate with a specific hardware device [1]; they are necessary because each device uses different commands and interfaces — the driver translates OS instructions into device-specific signals [1].
Q5Compare GUI and CLI interfaces. Give one advantage of each.[4]
✅ Mark scheme
GUI: uses windows, icons, menus, pointer [1]; advantage: easier for novice users / more intuitive [1]; CLI: text-based interface where commands are typed [1]; advantage: faster for experts, uses fewer system resources [1].
Q6Explain how multi-tasking works on a single-core CPU.[3]
✅ Mark scheme
A single-core CPU can only execute one process at a time [1]; the OS scheduler rapidly switches (time-slices) between processes [1]; each process gets a short time slot (quantum), giving the illusion that multiple programs run simultaneously [1].
Q7What is a real-time operating system? Give one example of where it is used.[2]
✅ Mark scheme
A real-time OS guarantees a response within a defined time constraint [1]; used in: aircraft flight control systems; pacemakers; anti-lock braking systems; industrial robots [1] (any valid example).
Q8Explain what "thrashing" means in the context of virtual memory.[3]
✅ Mark scheme
Thrashing occurs when the OS spends most of its time moving pages between RAM and virtual memory (disk) [1]; it happens when RAM is severely insufficient for the active processes [1]; the system becomes very slow because disk access is much slower than RAM [1].
?
out of 23 — self-mark above
Topic Quiz
Question 1 of 15
You scored
out of 15
Card 1 of 15
Click to reveal definition
🎉
Complete!
Term
Definition
🎯
Mini Test — 1.6.1a Operating Systems
10 questions · 10 marks · 10 minutes
⏱ 10:00
10 marks
Section A — Multiple Choice [5 marks]
Q1What does an operating system use to communicate with hardware devices?
Q2What does virtual memory use as an extension of RAM?
Q3What type of interface uses Windows, Icons, Menus, and a Pointer?
Q4What is "thrashing" in computing?
Q5Which type of OS guarantees a response within a set time limit, used in safety-critical systems?
Section B — Short Answer [5 marks]
Q6State two functions of an operating system.
Mark schemeAny two: Process management; Memory management; File management; Device/I/O management; User interface; Security management. [1 each]
Q7Explain what a device driver does.
Mark schemeA device driver translates OS commands into instructions that a specific hardware device can understand, allowing the OS to communicate with devices without needing device-specific code in the OS itself. [1]
Q8State one advantage of a CLI over a GUI.
Mark schemeFaster for experts; uses fewer system resources (RAM/CPU); allows automation through scripts; more control over the system. [1 for any valid advantage]
Q9Explain how a single-core CPU appears to run multiple programs at once.
Mark schemeThe OS scheduler rapidly switches (time-slices) between processes, giving each a short time slot (quantum). This happens so fast it appears simultaneous to the user. [1]
Q10Give one example of where an embedded OS might be used.
Mark schemeSmart TV; microwave controller; washing machine; digital camera; car engine management system; satellite navigation system. [1 for any valid example]