← IGCSE Computer Science Paper 1

Layers: applications, operating system, firmware and hardware

The layers of a computer: applications run on the operating system, which runs on firmware, which runs on hardware. Each layer depends on the layer below it.

Part of: IGCSE Computer Science 0478 — 4.1 Types of Software and Interrupts — Module 39

Understanding Layers: applications, operating system, firmware and hardware in IGCSE Computer Science Paper 1

What it does: The firmware sits above the hardware and below the operating system, and its bootloader starts the operating system running. The application does not control the disk directly. It requests a service from the operating system, the layer directly beneath it. Dependence goes downwards. Applications need the OS, the OS needs the firmware, and the firmware needs the hardware. The arrows show the dependency chain from the top layer (applications) down to the bottom layer (hardware).

Common mistakes: The third layer of the stack is firmware, which sits between the operating system and the hardware. Utility software is part of system software and is not a separate layer. It should be [ Firmware ]. An application runs on the operating system, not directly on the firmware. Line 2 should be: The browser runs on the OS.

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This module's key terms are also in a printable crossword (Modules 390–408) and word search (Modules 390–418).

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Learning
Duo
Which order lists the layers from the bottom (lowest) to the top?
Applications, operating system, firmware, hardwareHardware, firmware, operating system, applications
Matches
Hardware Operating system Firmware Applications
↓
The firmware and operating system are in the wrong order. The operating system runs on the firmware, so the firmware must sit between the hardware and the operating system.
Applying
Meanings
Term
software stack
Meaning
The layers of a computer: applications run on the operating system, which runs on firmware, which runs on hardware. Each layer depends on the layer below it.
Practice
Applications run on the operating system
Testing
Gaps
applications runs on
Check Answer
Spots
2[ Operating system ]
3[ Utility software ]

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Quick Questions

1. Which order lists the layers from the bottom (lowest) to the top?
A. Applications, operating system, firmware, hardware
B. Hardware, firmware, operating system, applications ✓
Hardware is the bottom layer. Firmware sits on it, the operating system runs on the firmware, and applications run on the operating system.
2. A web browser is an application. Which layer does it run directly on?
A. The hardware
B. The operating system ✓
Applications do not talk to the hardware directly. They ask the operating system, which manages the hardware for them.
3. Which statement is correct?
A. Each layer uses the services of the layer below it ✓
B. Each layer uses the services of the layer above it
Dependence goes downwards. Applications need the OS, the OS needs the firmware, and the firmware needs the hardware.
4. Which layer is at the very bottom of the stack?
A. Hardware ✓
B. Firmware
Hardware is the physical equipment. Firmware is software stored on hardware, so it sits one layer above.
5. Which layer sits directly between the hardware and the operating system?
A. Firmware (including the bootloader) ✓
B. Application software
The firmware, including the bootloader, runs on the hardware and loads the operating system.

Match the Pairs

Applications -> Operating system -> Firmware -> Hardware → Each layer runs on the one below it, so a program such as a web browser depends on every layer beneath it, down to the physical hardware.
Hardware (bottom) Firmware Operating system Applications (top) → A stack drawn from the bottom up: hardware is the base layer and applications are the top layer, which uses the services of all the layers below.
The bootloader in the firmware runs on the hardware and then loads the operating system. → Firmware: bootloader -> loads Operating system
A word processor asks the operating system to save a file, because applications use the services of the layer below. → Application -> Operating system: save file
Hardware Operating system Firmware Applications → The firmware and operating system are in the wrong order. The operating system runs on the firmware, so the firmware must sit between the hardware and the operating system.
Applications run directly on the Hardware, so the Operating system is not needed. → Applications do not run directly on the hardware. They need the operating system, which needs the firmware, which needs the hardware, so every layer depends on the one below.

Key Term

software stack
The layers of a computer: applications run on the operating system, which runs on firmware, which runs on hardware. Each layer depends on the layer below it.

Fill in the Blanks

1. applications runs on operating system
Hint: Type the software layer that applications depend on directly.
2. operating system runs on firmware
Hint: Type the layer just below the operating system, which holds the bootloader.
3. firmware runs on hardware
Hint: Type the physical bottom layer that the firmware runs on.
4. layer 1: hardware layer 2: firmware layer 3: operating system
Hint: Type the layer that sits directly above the hardware in the stack.
5. layer 3: operating system layer 4: applications
Hint: Type the layer number of the top layer, which sits above the operating system.

Spot the Error

Question 1
A [ Applications ]
B [ Operating system ]
C [ Utility software ]
D [ Hardware ]
Line C — The third layer of the stack is firmware, which sits between the operating system and the hardware. Utility software is part of system software and is not a separate layer. It should be [ Firmware ].
Question 2
A User opens a web browser
B The browser runs on firmware
C The OS runs on the firmware
D Firmware runs on the hardware
Line B — An application runs on the operating system, not directly on the firmware. Line 2 should be: The browser runs on the OS.
Question 3
A The game needs to play sound
B The OS asks the game to help
C The OS uses a sound driver
D The driver controls hardware
Line B — The dependency goes the wrong way. An application uses the services of the OS below it, so the game asks the OS to help, not the other way round.
Question 4
A stack ← []
B PUSH(stack, 'Hardware')
C PUSH(stack, 'Apps')
D PUSH(stack, 'OS')
E PUSH(stack, 'Apps')
Line C — The stack is built from the bottom up: hardware, firmware, OS, then applications. Pushing Apps on line 3 puts it on top of the hardware before the firmware. Line 3 should push 'Firmware'.
Question 5
A 1 Applications
B 2 Firmware
C 3 Operating system
D 4 Applications
Line A — The layers are numbered from the bottom up, so layer 1 is the hardware. Applications are the top layer, layer 4. Line 1 should be: 1 Hardware.

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