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This lesson covers the motherboard and the system bus (address bus, data bus, and control bus), as required by OCR J277 Section 1.1.1. Understanding how components communicate is essential for explaining how a computer system functions as a whole.
The motherboard is the main circuit board inside a computer. It is the physical foundation that connects all the components of a computer system together.
| Function | Description |
|---|---|
| Physical connections | Provides slots and sockets for the CPU, RAM, storage, and expansion cards |
| Communication pathways | Contains the buses (wires/traces) that allow components to send data to each other |
| Power distribution | Distributes electrical power from the power supply to all components |
| BIOS/UEFI chip | Contains the firmware needed to start the computer (boot process) |
The system bus is a collection of wires (also called traces on the motherboard) that carry signals between the CPU, memory, and other components. It consists of three separate buses:
| Property | Detail |
|---|---|
| Purpose | Carries the memory address that the CPU wants to access |
| Direction | Unidirectional — data flows only from the CPU to memory/devices |
| Width | Determines the maximum amount of memory the CPU can address |
How address bus width affects memory:
The width of the address bus (measured in bits) determines how many unique memory addresses the CPU can access:
OCR Exam Tip: The formula for calculating addressable memory is: Number of addresses = 2^n, where n is the width of the address bus in bits.
| Property | Detail |
|---|---|
| Purpose | Carries data between the CPU, memory, and I/O devices |
| Direction | Bidirectional — data can flow in both directions |
| Width | Determines how much data can be transferred in one operation |
How data bus width affects performance:
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