Role of operating systems
Describe the role of operating systems
In this lesson
- What an operating system is and where it sits between users, applications and hardware
- How the operating system abstracts (hides) the complexity of the hardware
- Which system resources the operating system manages, and why
LearnWhat an operating system is
Every general-purpose computer, from a phone to a server, runs an operating system (OS) such as Windows, macOS, Linux, Android or iOS.
LearnAbstracting the hardware
Abstraction means hiding the details that are not needed and showing only what is useful.
LabFollow a request through the layers
Step through each request from the user down to the hardware and back. Notice what each layer knows, and what it does not need to know.
- UserClicks, types and reads the screen
- ApplicationWord processor, browser, game
- Operating system (kernel)System calls, file system, scheduling, memory
- Device driverTranslates OS commands for one device
- HardwareCPU, RAM, SSD, keyboard, network card
Step 1 of 9 · User
The user presses Ctrl + S.
Follow two requests to the end to complete this activity.
LearnThe resources an OS manages
| Resource | What the OS does with it |
|---|---|
| Processor (CPU) time | Decides which process runs, for how long, and on which core (scheduling). |
| Main memory (RAM) | Gives each process its own memory, keeps processes apart and frees memory when a program ends. |
| Secondary storage | Organises data into files and folders, tracks free space and controls who may read or write each file. |
| Input/output devices | Controls keyboards, displays, printers and sensors through device drivers, and handles their interrupts. |
| Network | Sends and receives data for applications, and manages connections and addresses. |
The OS aims to use these resources efficiently (little is wasted), fairly (every program gets a share) and securely (programs and users can only use what they are allowed to).
CheckOS or application?
Which software is responsible for each task?
- Deciding which program runs on the CPU next
- Checking the spelling in an essay
- Finding free blocks on the SSD for a new file
- Applying a filter to a photo
- Stopping one program from reading another program's memory
- Sending commands to a printer through its driver
CheckQuick check
A school buys a new model of printer. What must be installed so that existing applications can print to it?
ExamWorked exam answer
Outline the difference between user mode and kernel mode.
[2]ReviewMistakes examiners see
The OS is not just the GUI. The windows and icons are one small part; most of the OS works out of sight.
Applications do not control hardware directly. They make requests (system calls) to the OS.
“The OS controls the computer” is too vague for marks. Name the resource (CPU time, memory, storage, devices) and say what the OS does with it.
For abstraction, give a concrete example: an application saves a file without knowing the type of drive or where the blocks are.
Exam practiceExam-style questions
5 questions · 14 marks. Answer each one first, then mark it yourself against the markscheme. Your answers are saved in this browser only.
A school replaces its old laptops with a new brand that has different storage drives, network cards and graphics hardware. The same operating system and applications are installed on the new laptops.
Identify two system resources that the operating system manages.
Outline what is meant by abstraction in the context of an operating system.
Explain why the school's applications run on the new laptops without being changed, even though the hardware is different.
A game on one of the new laptops crashes. Explain why the other applications and the operating system keep running.
Describe the role of the operating system on the new laptops.
0 of 5 questions marked. Mark every question to see your total.
Exam-style questions written for Praxis IB in the format of the 2027 specimen papers. They are not IB past-paper questions.