The operating system sits between your apps and the hardware, sharing out memory, the processor and devices, and keeping everything secure. Learn its nine functions and how hardware, firmware and the OS work together to run an application.
The operating system (OS) manages the computer's hardware and software and provides a platform for running applications. Its functions are: managing files, handling interrupts, providing an interface, managing peripherals and drivers, managing memory, managing multitasking, providing a platform for applications, providing system security and managing user accounts. Applications run on the OS, the OS is run on the firmware, and the firmware (the bootloader) runs on the hardware.
Fig. 1: applications run on the operating system, which is run on the firmware, which runs on the hardware
Section 01
What the OS does.
Learn the nine functions in the syllabus, and for each one be ready to say what the OS actually does.
Function
What the OS does
Managing files
creates, names, opens, saves, copies, moves and deletes files; organises them into folders (directories)
Handling interrupts
detects interrupt signals and runs the right interrupt service routine, by priority
Providing an interface
lets the user communicate with the computer, e.g. a graphical user interface (GUI) or command line interface (CLI)
Managing peripherals and drivers
uses device drivers to communicate with devices such as printers; manages buffers and queues of data to them
Managing memory
allocates RAM to programs and data, frees it when they close, and stops programs using each other's memory
Managing multitasking
shares processor time between several programs so they appear to run at the same time
Platform for running applications
loads applications and gives them services (files, memory, devices) so they do not control hardware directly
Providing system security
e.g. firewall, access rights, automatic security updates, logins
Managing user accounts
creates accounts with usernames and passwords, keeps each user's files and settings separate
Examiner trap
"It manages memory" on its own often scores nothing. Add the detail: it allocates memory to each program and stops programs overwriting each other's memory.
Section 02
From power on to app.
An application cannot talk to the hardware directly. It needs a stack of layers, set up in order when you switch on.
Hardware: the physical parts: CPU, RAM, storage, input and output devices.
Firmware: software stored permanently in non-volatile memory (ROM) on the hardware. The bootloader is firmware: it runs when the power comes on, checks the hardware and loads the OS from storage into RAM.
Operating system: once loaded, it is run on the firmware and manages the hardware.
Applications: are run on the OS, which gives them memory, processor time, files and access to devices.
Worked example Start-up order
Describe how hardware, firmware and the operating system allow a user to open a word processor.
Power on: the hardware runs the bootloader, firmware stored in ROM.
The bootloader loads the operating system from secondary storage into RAM and starts it.
The OS is run on the firmware and takes control of the hardware.
The user opens the word processor; the OS loads it into memory and it runs on the OS, using the OS's services.
Answer: Hardware runs the bootloader (firmware); the bootloader loads the OS; the application runs on the OS.
Examiner trap
The bootloader is firmware, not the operating system. The OS is usually stored on the SSD or hard disk, not in ROM.
Stage 1 · Learn
Check what the sim just showed you
Four quick checks. Each correct answer earns XP and records this skill on your profile.
Quick check+10 XP
Which is a function of an operating system?
Quick check+10 XP
What is the bootloader?
Quick check+10 XP
Which layer does an application run on directly?
Quick check+10 XP
What does the OS use to communicate with a peripheral such as a printer?
Section 03
Spot the function.
Exam questions often describe something happening and ask which OS function it is.
Worked example Match the function
Which OS function is shown? (a) A user plays music while typing an essay. (b) A new printer is plugged in and works. (c) Two students log in to the same PC and see different desktops.
(a) Two programs share the processor and appear to run together: managing multitasking.
(b) The OS installs and uses a device driver to communicate with the printer: managing peripherals and drivers.
(c) Each user has their own account with separate files and settings: managing user accounts.
Answer: (a) multitasking (b) peripherals and drivers (c) user accounts
Your turn
A user drags a document into a folder called Homework. Which OS function is this?
Managing files: the OS moves the file and organises it in the folder structure.
Stage 2 · Exam
Exam-style questions
Unlocks once the four checks above are done. Worth more XP, written to IGCSE Paper 1 standard.
Finish the four checks above to unlock the exam questions
Exam style+20 XP
A computer lets a user stream music while editing a document. Which OS function makes this possible?
Exam style+20 XP
Where is firmware stored?
Exam style+20 XP
Which describes the OS function "providing an interface"?
Exam style+20 XP
Which is an example of the OS providing system security?
Skill unlocked
The operating system, mastered.
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