Learning Objectives
- Explain the relationship between hardware, firmware, the operating system and application software.
- Explain the role of firmware during computer start-up.
- Explain the function of a bootloader.
- Describe the sequence from powering on the hardware to running an application.
- Apply the layered model to explain why an application cannot normally run by itself.
Key Terms
- Hardware
- The physical electronic and mechanical components of a computer system.
- Firmware
- Software stored in non-volatile memory that provides low-level control and start-up instructions for hardware.
- Bootloader
- Firmware code that starts the process of loading the operating system.
- Booting
- The process of starting a computer and loading the operating system.
- Non-volatile memory
- Memory that retains its contents when power is removed.
- Operating system
- System software that manages resources and provides a platform for applications.
- Application software
- Software that provides services or tasks required by the user.
- Software layer
- One level of software that uses services provided by a lower level and provides services to a higher level.
A Layered Computer System
A working computer system depends on several layers. The physical hardware forms the base. Firmware stored in non-volatile memory can run as soon as the processor starts. The firmware starts the boot process and enables the operating system to be loaded. Applications then run on the operating system.
The required Cambridge relationship can be summarised as: the bootloader firmware runs on the hardware; the operating system is run on or started through the firmware; applications are run on the operating system. Each upper layer depends on services and control supplied below it.
The layers simplify system design. An application can request a file or display service from the operating system. The OS can use drivers and lower-level routines to control hardware. Firmware supplies the first instructions needed before the full operating system is available.
Firmware And The Bootloader
Firmware is software closely associated with hardware and stored in non-volatile memory. Because it remains present when the power is off, it is available immediately when the computer is switched on. It can initialise essential hardware and begin the start-up sequence.
The bootloader is firmware code responsible for locating and starting the operating system. It identifies where the operating-system code is stored, loads the required part into main memory and transfers control so that the operating system can continue the start-up process.
The bootloader is not the complete operating system. It performs a limited start-up role. Once the OS is loaded, the operating system takes responsibility for managing files, memory, peripherals, multitasking, interfaces, security, user accounts and applications.
From Power-On To Application
When power is applied, the processor begins executing start-up instructions held in firmware. The firmware checks or initialises essential hardware and runs the bootloader. The bootloader locates the operating system on storage and loads the required code into main memory.
After the operating system starts, it initialises drivers and system services, manages resources and presents a user interface or sign-in process. When the user starts an application, the OS loads the application’s instructions and data into memory and creates a process.
The application then uses operating-system services to receive input, display output, access files and use peripherals. If any required layer is missing or incompatible, the application may not run. For example, hardware without suitable firmware may not start correctly, and an application built for a different operating-system platform may not have the services it expects.
Why The Distinction Matters
Hardware is physical, while firmware, operating systems and applications are software. Firmware differs from ordinary applications because it provides low-level hardware control and start-up instructions. The operating system differs from applications because it manages the system and supplies the environment in which applications run.
An examination question may ask for the order or relationship. A high-quality answer names every layer and explains dependence: hardware executes firmware; the firmware bootloader loads the OS; the OS manages resources and provides the platform; the application uses that platform to perform a user task.
Do not describe the layers as completely separate. They interact continuously. The application requests services from the OS; the OS controls hardware using drivers and low-level mechanisms; firmware may continue to provide basic hardware routines even after start-up.
Layers Required To Run An Application
| Layer | Main Role | Depends On |
|---|---|---|
| Application software | Performs a task required by the user. | Operating-system services and platform. |
| Operating system | Manages resources and provides system services. | Firmware, drivers and functioning hardware. |
| Firmware and bootloader | Provides low-level start-up control and loads the OS. | Processor and other hardware. |
| Hardware | Executes instructions and stores or transfers data. | Electrical power and valid controlling instructions. |
Simplified Boot Sequence
| Order | Event |
|---|---|
| 1 | Power is applied and the processor begins executing firmware. |
| 2 | Firmware initialises essential hardware and runs the bootloader. |
| 3 | The bootloader locates and loads the operating system into main memory. |
| 4 | The operating system starts services, drivers, security and the user interface. |
| 5 | The OS loads an application when the user starts it. |
Worked Examples
Explaining A Start-Up Failure
Question: A computer has working hardware but no valid bootloader. Explain why the operating system cannot start.
- The processor can begin executing firmware on the hardware.
- The bootloader is the firmware component that locates and loads the operating system.
- Without a valid bootloader, control cannot be transferred to the operating-system code.
Answer: The hardware can power on, but the start-up sequence cannot locate and load the operating system because the bootloader is missing or invalid.
Why An Application Needs The OS
Question: Explain why a photo-editing application normally cannot run directly on bare hardware.
- The application expects services for files, display, input, memory and peripherals.
- These services are provided and coordinated by the operating system.
- The OS also uses drivers and hardware-control mechanisms on the application’s behalf.
Answer: The application depends on the operating-system platform to manage resources and provide standard access to the hardware.
Examination Guidance
- Write the layers in the correct order: hardware, firmware or bootloader, operating system, application.
- State that the bootloader loads the operating system; do not say it is the whole operating system.
- Use non-volatile memory when explaining why firmware is available immediately at power-on.
- When asked how applications run, mention that they use services provided by the operating system.
- Explain the relationship rather than producing a list of definitions only.
Common Mistakes
- Saying firmware is a physical hardware component.
- Saying an application is loaded before the operating system.
- Confusing the bootloader with a device driver.
- Claiming the operating system is stored only in volatile RAM at all times.
- Saying firmware is always a user-installed application.
Knowledge Check
1. What is firmware?
2. What does a bootloader do?
3. On what does application software normally run?
4. Why must firmware be stored in non-volatile memory?
5. State the simplified layer order.
