Computer Architecture - System Bus (address, data & control)

Summary

The system bus is a crucial term referring to the combined data, address, and control buses in a computer's architecture. The data bus is bi-directional, transporting data and instructions between components. The address bus is one-directional, sending address signals from the CPU to memory. The control bus, also bi-directional, carries control signals to manage operations between devices. These buses facilitate communication between the CPU, memory, and input/output devices. Understanding their roles and directionality is vital for grasping how data flows within a system.

Takeaways

• 😀 The system bus refers to all three buses working together: the data bus, address bus, and control bus.
• 😀 The data bus is bi-directional, allowing data and instructions to travel both to and from the processor.
• 😀 The data bus is essentially a collection of wires that carry ones and zeros, representing data and instructions.
• 😀 The address bus is unidirectional, sending address signals from the CPU to memory or other components.
• 😀 The address bus carries specific addresses so the CPU can request data or instructions from memory.
• 😀 The control bus is bi-directional, carrying control signals between components such as the CPU and memory.
• 😀 Examples of control signals include interrupt requests and clock timing, which help manage the operations of the system.
• 😀 The three-box model consists of the CPU, main memory (ROM and RAM), and I/O controllers (e.g., input/output devices like keyboards and printers).
• 😀 The CPU uses the data bus to send and receive data from various components, including memory and I/O devices.
• 😀 The address bus only carries addresses from the CPU, but the actual data is transferred over the data bus once the address is received.
• 😀 The control bus sends signals to coordinate actions, such as telling the memory whether to read or write data based on the address and control signals.

Q & A

What is meant by the term 'system bus'?

The term 'system bus' refers to the collective name for three different buses: the data bus, address bus, and control bus. Together, they facilitate communication between the CPU, memory, and input/output (I/O) controllers.

What is the primary function of the data bus?

The data bus is responsible for transporting data and instructions between components on the motherboard. It is bi-directional, meaning it can send and receive data to and from the processor.

How does the address bus differ from the data bus?

The address bus is unidirectional, meaning it only sends address signals from the CPU to memory or I/O devices. It is used to specify the location of data or instructions in memory, whereas the data bus carries the actual data or instructions.

What is the role of the control bus?

The control bus carries control signals between components. It is bi-directional and includes signals like clock timings and interrupt requests, which help coordinate operations between the CPU, memory, and I/O devices.

Why is the data bus bi-directional?

The data bus is bi-directional because it needs to send and receive data. It can carry information from the CPU to other components (e.g., memory) and vice versa.

Can you give an example of how the address bus works?

When the CPU wants to retrieve data from a specific location in memory, it sends the address of that location through the address bus. The memory responds by sending the data at that address back to the CPU, but this data travels through the data bus, not the address bus.

Why is the control bus bi-directional?

The control bus is bi-directional because it must carry control signals both to and from the CPU. For example, the CPU sends a 'read' or 'write' control signal to memory, and it may also receive interrupt signals to pause its current operations.

What happens if only the address is sent to memory, but no control signal is provided?

If only an address is sent to memory without a control signal, the memory won't know what to do with the address. The control signal specifies whether to read or write data at that address, ensuring proper operation.

What is the 'three box model' mentioned in the video?

The 'three box model' is a conceptual diagram that illustrates the relationships between the CPU, main memory (ROM and RAM), and I/O controllers. It helps to visualize how data flows between these components via the system bus.

How do I/O devices like a keyboard communicate with the CPU?

I/O devices like a keyboard send data to the CPU through the data bus. For example, when a key is pressed, the keyboard sends the corresponding data (such as a letter) to the CPU for processing.