Year 11 · Computer Science · Autumn 1
Software · Lesson 2 of 5
Firmware, the boot process and interrupts
Theory4.1 Types of software and interrupts
Year 11 · Computer Science · Software · Lesson 2 of 5
You will learn to
- Describe how the bootloader, stored as firmware, loads the operating system at start-up.
- Explain how applications, the operating system, firmware and hardware work as layers.
- Describe how an interrupt is handled: save the current task, run the ISR, then carry on.
- Give examples of hardware interrupts and software interrupts.
Year 11 · Computer Science · Software · Lesson 2 of 5
Success criteria
You have got it when you can say:
- I can put the steps from power on to desktop in the right order.
- I can say which layer each part runs on: application, OS, firmware, hardware.
- I can describe the three stages of handling an interrupt.
- I can give one hardware interrupt and one software interrupt.
Year 11 · Computer Science · Software · Lesson 2 of 5
Retrieval starter
Questions from before. Write your answers, then show them.
- Last lesson
A compiler…
A Translates the whole program once into machine codeB Translates one line at a time, every runC Only checks spelling
A. Translates the whole program once into machine code
- Last year
A solid-state drive…
A Uses spinning plattersB Has no moving partsC Uses a laser
B. Has no moving parts
- Last lesson
An interpreter stops…
A At the first error it meetsB NeverC Only after translating everything
A. At the first error it meets
Year 11 · Computer Science · Software · Lesson 2 of 5
Key words (1 of 4)
- System software
- Software that runs and manages the computer, such as the operating system and utilities.
- Application software
- Software that does a task for the user, such as a word processor or game.
- Operating system (OS)
- System software that manages the hardware, files, memory and programs, and gives the user an interface.
Year 11 · Computer Science · Software · Lesson 2 of 5
Key words (2 of 4)
- Device driver
- A small program that lets the OS communicate with one particular device.
- Multitasking
- Running several programs by giving each a short turn on the processor, so they seem to run at once.
- Firmware
- Software stored permanently in ROM or flash memory on the hardware.
- Bootloader
- Firmware that loads the operating system into RAM when the computer is switched on.
Year 11 · Computer Science · Software · Lesson 2 of 5
Key words (3 of 4)
- Interrupt
- A signal to the processor that something needs its attention.
- Interrupt service routine (ISR)
- A small program that deals with one type of interrupt.
- Compiler
- A translator that turns the whole high-level program into machine code at once and creates an executable file.
Year 11 · Computer Science · Software · Lesson 2 of 5
Key words (4 of 4)
- IDE
- Integrated development environment: one program with the tools to write, translate, run and debug code.
The explanation · step 1 of 9 · part 1 of 3
Two kinds of software
Software is a set of instructions that tells the hardware what to do. There are two main kinds.
System software runs and looks after the computer itself. The user often does not notice it working.
Application software does a job the user wants done, such as writing an essay or editing a photo.
Application software needs system software underneath it. A word processor cannot run without an operating system.
The explanation · step 1 of 9 · part 2 of 3
Two kinds of software (continued)
| System software | Application software | |
|---|---|---|
| Purpose | Runs and manages the computer | Does a task for the user |
| Examples | Operating system, device drivers, utilities (anti-virus, backup, disk defragmenter), compilers | Word processor, spreadsheet, web browser, video game, photo editor |
| Who it serves | The computer and the programs on it | The user |
System software hides the hard parts of the hardware. That means the people who write apps do not need to know how every printer or disk works.
The explanation · step 1 of 9 · part 3 of 3
Two kinds of software (continued)
A web browser is application software, even though it feels like part of the computer. Ask: does it do a task for the user? If yes, it is an application.
The explanation · step 2 of 9 · part 1 of 3
The operating system and its nine functions
The operating system (OS) is the most important piece of system software. Examples are Windows, macOS, Linux, Android and iOS.
It sits between the user, the applications and the hardware. It manages everything so that they all work together.
Cambridge lists nine functions. Learn all nine, with an example for each.
The explanation · step 2 of 9 · part 2 of 3
The operating system and its nine functions (continued)
| OS function | What it means in plain words | Example |
|---|---|---|
| Managing files | Lets you create, name, save, open, copy, move and delete files and folders | Saving `essay.docx` into a folder called `English` |
| Handling interrupts | Responds to signals that need the processor's attention | Pausing a game when you press Esc |
| Providing an interface | Gives the user a way to talk to the computer | Icons, windows and menus (GUI) or typed commands (CLI) |
| Managing peripherals and drivers | Talks to devices such as printers through driver software | Installing a driver so a new printer works |
| Managing memory | Decides which program uses which part of RAM | Keeping a browser and a music app in separate areas of RAM |
| Managing multitasking | Shares processor time so several programs seem to run at once | Music plays while you type |
| Providing a platform for running applications | Gives apps a stable base and services they can use | An app asks the OS to save a file instead of controlling the disk itself |
| Providing system security | Protects the computer and its data from threats | Built-in firewall, security updates, login screen |
| Managing user accounts | Keeps each user's files, settings and permissions separate | A student account cannot install software; an admin account can |
The explanation · step 2 of 9 · part 3 of 3
The operating system and its nine functions (continued)
In the exam, "manages files" alone may not get a mark. Add what it does, for example "lets the user rename and delete files".
The explanation · step 3 of 9 · part 1 of 4
Files, interface, peripherals and drivers
Managing files. The OS keeps track of where each file is stored on the disk. It organises files into folders and controls who can open them.
Providing an interface. A GUI (graphical user interface) uses windows, icons, menus and a pointer. A CLI (command line interface) uses typed commands. A GUI is easier to learn; a CLI is faster for experts.
The explanation · step 3 of 9 · part 2 of 4
Files, interface, peripherals and drivers (continued)
Peripherals are devices connected to the computer, such as a printer, keyboard or webcam. A device driver is a small program that translates between the OS and one particular device.
The OS also uses buffers and queues for slow devices. For example, it holds a print job in a queue until the printer is ready.
The explanation · step 3 of 9 · part 3 of 4
Files, interface, peripherals and drivers (continued)
The explanation · step 3 of 9 · part 4 of 4
Files, interface, peripherals and drivers (continued)
Without drivers, the OS would need to know the details of every device ever made. Drivers mean a new device only needs one new small program.
The explanation · step 5 of 9 · part 1 of 2
Platform, security and user accounts
Providing a platform for running applications. Apps do not control hardware directly. They ask the OS to do things for them, such as "save this file" or "show this window".
This is why an app written for Android will not run on iOS. Each app is written for one platform.
Providing system security. The OS asks for a password or fingerprint at login. It installs security updates and can run a firewall and anti-malware.
The explanation · step 5 of 9 · part 2 of 2
Platform, security and user accounts (continued)
Managing user accounts. Each user has a username and password. The OS keeps their files and settings apart and gives each account its own access rights (what it is allowed to do).
The explanation · 5 more steps
More on the lesson page
The lesson page has the rest of the explanation, step by step:
- Memory and multitasking
- The layers: hardware, firmware, OS, applications
- What an interrupt is and how it is generated
- How the processor handles an interrupt
- After the ISR: what happens next
Year 11 · Computer Science · Software · Lesson 2 of 5
Quick quiz · 1 of 3
Which is a low-level language?
- A Java
- B Assembly language
- C Python
B. Assembly language
Assembly is close to the chip. An assembler turns it into machine code.
Year 11 · Computer Science · Software · Lesson 2 of 5
Quick quiz · 2 of 3
An IDE provides…
- A The operating system
- B Only the keyboard
- C An editor, a run button and a debugger
C. An editor, a run button and a debugger
Integrated development environment: everything for writing code in one app.
Year 11 · Computer Science · Software · Lesson 2 of 5
Quick quiz · 3 of 3
Which of these is system software?
- A A word processor
- B The operating system
- C A game
B. The operating system
System software runs the computer. Applications do jobs for people.
Year 11 · Computer Science · Software · Lesson 2 of 5
Exit ticket
Answer on paper before you go. Then check.
The bootloader…
A Prints documentsB Loads the operating system from storage into RAM at start-upC Translates Python
B. Loads the operating system from storage into RAM at start-up It lives in ROM and runs first when the power comes on.
An interrupt is…
A A signal that makes the CPU pause and deal with somethingB A type of virusC A loop that never ends
A. A signal that makes the CPU pause and deal with something A key press or a printer out of paper. The CPU saves its place, handles it, carries on.