Describe the purpose of an operating system — what it does and why it is needed — and explain the role it plays as an interface between software and hardware
Explain how the OS manages memory — allocating RAM to programs and using virtual memory when physical RAM runs out
Describe how the OS handles file management — organising, naming, and controlling access to files stored on secondary storage
Explain multi-tasking and how the OS schedules processor time across multiple running programs simultaneously
Describe user management — creating accounts and access levels — and explain the role of peripheral management and drivers in allowing hardware devices to communicate with the OS
⚡ Topic 1.5.1 — the OS is the software that manages all hardware and software resources on a computer.
Systems Software
What is an operating system?
DEFINITION
An operating system (OS) is software that manages the hardware and software resources of a computer. It provides a platform for applications to run on, and acts as an interface between the user, the software applications, and the hardware.
Applications would have to directly control hardware — every program would need to know how to talk to every possible screen, keyboard, storage device, and printer. The OS abstracts this away.
⚡ Examples: Windows, macOS, Linux, Android, iOS. The OS is system software — it runs constantly in the background, managing everything else.
OS Function
Memory management
DEFINITION
Memory management is the process by which the OS allocates portions of RAM to programs that need it, keeps track of which areas of memory are in use and which are free, and reclaims memory when programs close or no longer need it.
HOW IT WORKS
When a program runs, the OS allocates a block of RAM for it to use. Each program is given its own protected area of memory — one program cannot read or overwrite another program's memory space.
The OS keeps a memory map — a table of which memory addresses are in use by which processes. When a program closes, its memory is freed and made available for other programs.
VIRTUAL MEMORY
When physical RAM is full, the OS uses virtual memory — a section of the hard drive (or SSD) that is treated as an extension of RAM. Data that hasn't been used recently is temporarily moved (swapped out) from RAM to virtual memory on the drive, freeing up RAM for the currently active programs. When that data is needed again, it is swapped back in.
⚡ Virtual memory is much slower than RAM because storage is slower than RAM. If a computer relies heavily on virtual memory, it will slow down noticeably — this is sometimes called "thrashing."
OS Function
File management
DEFINITION
File management is the way the OS organises, stores, retrieves and controls access to files on secondary storage. It provides a structured system — typically a hierarchical folder structure — that allows users and applications to locate and use data efficiently.
FILE SYSTEM RESPONSIBILITIES
📁
ORGANISATION
Maintains a hierarchical directory (folder) structure — files are stored in folders, which can be nested within other folders. Each file has a unique path (e.g. C:\Users\Documents\file.txt)
🏷️
NAMING AND METADATA
Stores file names, extensions (e.g. .docx, .jpg), size, date created/modified, and location on the storage device
🔐
ACCESS CONTROL
Controls which users can read, write, or execute each file — enforcing permissions set by the OS user management system
⚡ The file system is what you interact with every time you open File Explorer or Finder. The OS handles all the low-level reading and writing to storage — your application just asks for a file by name.
OS Function
Multi-tasking
DEFINITION
Multi-tasking is the ability of the OS to run multiple programs apparently simultaneously. The OS divides processor time between running processes — switching between them so rapidly that to the user it appears all programs are running at the same time.
HOW IT WORKS — SCHEDULING
The OS uses a scheduler to decide which process gets CPU time, for how long, and in what order. Each process is given a small slice of CPU time — called a time slice — before the scheduler switches to the next process.
Because CPUs execute billions of instructions per second, this switching happens so fast — typically milliseconds — that users experience all programs as running simultaneously, even on a single-core processor.
PROCESS STATES
Each process can be in one of three states: Running — currently using the CPU. Ready — waiting for CPU time. Blocked/Waiting — waiting for input or a resource.
CONTEXT SWITCHING
When the CPU switches from one process to another, it saves the current process's state (registers, program counter) — this is called a context switch. When the process gets CPU time again, it continues exactly where it left off.
⚡ Multi-tasking is managed by the OS — not by application software. The OS scheduler decides which programs get CPU time and for how long. Applications simply run; the OS coordinates everything underneath.
OS Function
User management
DEFINITION
User management allows the OS to support multiple users on the same system, each with their own account, personal settings, files, and level of access. The OS controls what each user can see and do — enforcing security and privacy between accounts.
WHAT USER MANAGEMENT PROVIDES
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USER ACCOUNTS
Each user has a unique username and password — their identity on the system. The OS stores each user's personal settings, desktop, and documents separately
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AUTHENTICATION
The OS verifies who the user is at login — via password, PIN, or biometrics — before granting access to the system and that user's resources
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ACCESS LEVELS & PERMISSIONS
Standard users, administrators, and guests each have different permissions — controlling which files, settings, and programs each account can access
PRIVACY
Each user's files and folders are kept private from other users. User A cannot access User B's Documents without administrator permission.
SECURITY
Limiting users to what they need (least privilege) reduces the damage a compromised account can cause. Admins can add, remove, and manage accounts centrally.
⚡ User management in the OS is the technical implementation of the user access levels you studied in 1.4.2. The OS enforces those permissions at the system level — software and files respect the rules the OS sets.
OS Function
Peripheral management & drivers
DEFINITION
Peripheral management is how the OS controls input and output devices — keyboards, mice, printers, monitors, and other hardware. A driver is a small piece of software that allows the OS to communicate with a specific hardware device.
WHAT IS A DRIVER?
Every peripheral device has its own way of communicating — its own protocol and command set. A driver acts as a translator between the OS and the specific device, converting the OS's generic commands into the precise instructions that device understands.
Without the correct driver installed, the OS cannot communicate with the peripheral — the device will not function. When you plug in a new printer, the OS looks for the matching driver before the printer can be used.
HOW PERIPHERALS COMMUNICATE
Applications request hardware operations (e.g. "print this"). The OS passes the request to the appropriate driver. The driver sends device-specific commands to the hardware, which performs the action and returns a status.
WHY DRIVERS MATTER
Different devices from different manufacturers each need their own driver. The OS itself stays the same — only the driver changes. This is why you sometimes need to install drivers when connecting a new device.
⚡ Key distinction: the OS manages peripherals at a high level (which device to use, when). A driver handles the low-level communication with one specific device. Without the right driver, the OS cannot talk to the hardware.
OS Function
User interfaces: GUI vs CLI
THE OS PROVIDES A USER INTERFACE
Part of the OS's job is to provide a way for users to interact with the computer. Two main types exist: the Graphical User Interface (GUI) and the Command Line Interface (CLI).
GUI — GRAPHICAL USER INTERFACE
Windows, macOS, Android, iOS
✓ Visual elements — icons, menus, windows, buttons
✓ Operated with mouse, touchpad, or touchscreen
✓ Easy to learn — intuitive for beginners
✓ No commands to memorise
✗ Uses more RAM and processing power
✗ Slower for complex or repeated tasks
CLI — COMMAND LINE INTERFACE
Linux Terminal, Windows Command Prompt
✓ Text-only — user types commands directly
✓ Uses very little RAM — fast and efficient
✓ Powerful for scripting and automation
✓ Precise control over the system
✗ Steep learning curve — commands must be memorised
✗ Easy to make errors — no visual feedback
🖥️ GUI — home users, office software, schools. Anywhere ease of use matters over performance.
💻 CLI — server administrators, developers, automated scripts, systems with limited resources.
⚡ Both GUI and CLI are provided by the OS. Many operating systems offer both — e.g. Windows has both a graphical interface and a command prompt. GUI = easier for general users; CLI = more powerful for technical users.
Exam Application
OS functions in context
Scenario A
A user has 16 tabs open in a browser, a video editing program running, and a music player in the background. They notice the computer is running slowly. Identify the OS function involved and explain why performance has degraded.
MEMORY MANAGEMENT / MULTI-TASKING
The OS is managing memory for many concurrent processes. Physical RAM may be full — the OS is using virtual memory (swap space on the drive), which is much slower than RAM. The scheduler is also dividing CPU time across many processes. Both memory and multi-tasking pressure are reducing performance.
Scenario B
A teacher connects a new interactive whiteboard to a school computer. The computer does not respond to the whiteboard. What is most likely missing, and which OS function does this relate to?
PERIPHERAL MANAGEMENT — MISSING DRIVER
The OS cannot communicate with the whiteboard because the correct driver has not been installed. A driver is software that acts as a translator between the OS and a specific hardware device. Without it, the OS has no way to send commands to or receive data from the whiteboard. Installing the manufacturer's driver would resolve the issue.
Putting It Together
Operating Systems — the big picture
PURPOSE & ROLE
The OS manages all hardware and software resources. It acts as the interface between user/applications and hardware. Without it, programs would have to directly control hardware.
MEMORY MANAGEMENT
Allocates RAM to programs; tracks used and free memory; reclaims memory when programs close. Virtual memory uses storage as extra RAM when physical RAM is full — slower but prevents crashes.
FILE MANAGEMENT
Hierarchical folder structure. Stores file name, path, size, date, permissions. Supports create, read, write, delete, copy, rename. Controls which users can access which files.
MULTI-TASKING & USER MANAGEMENT
Multi-tasking: scheduler divides CPU time between processes via time slices — appears simultaneous. User management: separate accounts with authentication and permissions — least privilege enforced at OS level.
PERIPHERAL MANAGEMENT, DRIVERS & INTERFACES
OS manages peripherals via drivers — translator software for each specific device. Without the correct driver, the device does not work. GUI (graphical, easy, more resources) vs CLI (text-based, efficient, powerful for experts).
Exam-Style Questions
Operating Systems
Question 1
Describe the purpose of an operating system.
2 marks
1
An operating system manages the hardware and software resources of a computer. (1 mark)
1
It acts as an interface between the user/applications and the hardware, allowing programs to run without needing to directly control the hardware. (1 mark)
Question 2
Explain what a driver is and why it is needed.
2 marks
1
A driver is software that allows the operating system to communicate with a specific hardware device / peripheral. (1 mark)
1
Each device has its own way of communicating — the driver acts as a translator between the OS's generic instructions and the specific commands that device understands. Without the driver, the OS cannot use the device. (1 mark)
Question 3
A computer with 8 GB of RAM is running many programs at once and has become very slow. Explain how virtual memory is being used and why this causes the computer to slow down.
3 marks
Common Mistakes
Four mistakes that cost marks in the exam
1
Describing virtual memory as extra RAM. Virtual memory is a section of secondary storage (hard drive or SSD) that the OS uses as an extension of RAM when physical RAM is full. It is not additional RAM — it is far slower. Never say "virtual memory increases the amount of RAM" — it simulates extra memory at the cost of speed.
2
Confusing multi-tasking with multi-core processing. Multi-tasking is the OS's ability to rapidly switch the CPU's attention between multiple processes — even on a single-core processor. Multi-core is a hardware feature where the CPU has multiple cores that can run processes truly simultaneously. They are related but not the same.
3
Saying a GUI is "better" than a CLI. Neither is better — they suit different situations. A GUI is easier for general users but uses more resources. A CLI is harder to learn but more efficient and powerful for experienced users. In exam answers, always give context — say "more appropriate for" rather than "better."
4
Confusing the OS with application software. The OS (Windows, macOS, Linux) is system software — it manages resources and provides a platform for other software to run on. Application software (Word, Chrome, Photoshop) runs on top of the OS. The OS is not a program you use to write documents or browse the web — it is the foundation everything else runs on.
Summary
1.5.1 — Operating Systems
PURPOSE
Manages hardware and software resources. Interface between user/applications and hardware. Examples: Windows, macOS, Linux, Android, iOS.
MEMORY MANAGEMENT
Allocates RAM to programs. Virtual memory = storage used as extra RAM when RAM is full. Slower than RAM.
FILE MANAGEMENT
Hierarchical folders, file metadata (name/size/date/type). Operations: create, read, write, delete, copy, rename. Access control per user.
MULTI-TASKING & USER MANAGEMENT
Multi-tasking: scheduler gives each process CPU time slices — appears simultaneous. User management: accounts, authentication, permissions (least privilege).
EXAM TIP
Drivers = translator software for specific hardware. Without driver → device doesn't work. GUI = graphical, easier, more resources. CLI = text-based, efficient, steep learning curve. Virtual memory ≠ extra RAM — it's storage pretending to be RAM.