Cambridge O Level Computer Science · Syllabus 2210 · Software
Bootloader
What is Bootloader?
A bootloader is the part of the firmware that runs when a device is switched on. It performs the initial start-up tasks, locates the operating system, loads it into main memory and then transfers control to it.
This definition is part of the Software chapter in Cambridge O Level Computer Science.
Bootloader in context
A computer is built in layers, and each layer only works because the layer beneath it is already running. Hardware executes machine instructions and nothing else. Firmware, held in non-volatile memory, starts the hardware and its bootloader loads the operating system. The operating system then manages files, memory, peripherals, users and security, and provides the platform on which application software runs. While all of that is happening, interrupts let an urgent event — a key press, a division by zero — reach the CPU without it having to keep asking. And because a CPU can only execute machine code, every program a person writes must first be put through a translator: an assembler, a compiler or an interpreter.
Application software cannot run on its own. Applications run on the operating system; the operating system runs on the firmware; and the bootloader — which is part of the firmware — runs on the hardware. Each layer depends on the one below it being present and working. Firmware is the only software that is already there when the power arrives, which is why it, and not the operating system, is what starts the machine.
Common mistakes with Bootloader
- 1. Inverting the stack. Why it fails Writing that "the operating system loads the firmware" or "the operating system starts first" reverses the only ordering the syllabus states. Firmware is already present in non-volatile memory when the power arrives; the operating system is a file on secondary storage that something has to fetch. Fix Rehearse the order upward: hardware → bootloader in firmware → operating system → applications. See section 4.1 E.
- "Firmware and the operating system are the same thing." Correct model They are different software with different jobs, held in different places. Firmware is in non-volatile memory, is tied to that specific hardware, and starts the machine. The operating system is on secondary storage, is loaded into main memory by the bootloader, and then manages the machine.
- "The operating system starts before the firmware." Correct model Impossible. The operating system has to be loaded from storage, and the thing that loads it is the bootloader, which is part of the firmware. Firmware is already present when the power arrives; the operating system is not.
- M4. "Firmware and the operating system are identical." Why it fails They are stored in different places, run at different times and do different jobs. Merging them makes the start-up sequence impossible to describe. Corrected model Firmware is in non-volatile memory, is tied to that specific hardware, and provides the initial control. The operating system is on secondary storage, is loaded into main memory by the bootloader, and then manages the whole machine. Exam-safe sentence "Firmware provides the initial control of the hardware and its bootloader loads the operating system; the operating system then manages the computer's resources." Show the retrieval checkHide the check Check: Where is firmware stored, and where is the operating system stored before it runs?Answer: Firmware is in non-volatile memory on the device; the operating system is on secondary storage until the bootloader loads it into main memory.
- M5. "The operating system starts before firmware." Why it fails It is not merely conventional but impossible. The operating system has to be loaded from storage, and loading requires a program that is already running. The only software already present when the power arrives is the firmware. Corrected model Hardware → firmware (including the bootloader) → operating system → applications. The bootloader in firmware runs on the hardware, the operating system runs on the firmware, and applications run on the operating system. Exam-safe sentence "The bootloader, which is part of the firmware, runs on the hardware and loads the operating system into main memory; applications then run on the operating system." Show the retrieval checkHide the check Check: Why can the operating system not be the first software to run?Answer: Because it is on secondary storage and must be loaded into main memory, and loading it requires a program that is already running — the bootloader in firmware.
Questions students ask about Bootloader
In what order do hardware, firmware, the operating system and applications start up?
Applications run on the operating system, the operating system runs on the firmware, and the bootloader, which is part of the firmware, runs on the hardware. Firmware is held in non-volatile memory and is already present when the power arrives, so its bootloader is what loads the operating system into main memory from secondary storage. The operating system cannot start first, because it has to be loaded by a program — the bootloader — that is already running.