Lecture Notes on Bus Architecture

What is a Bus?

• A bus is a communication pathway connecting two or more devices.
• It allows communication between major components such as processor, memory, and I/O devices.

System Bus

• A bus connecting major components like processor, memory, and I/O devices.
• Typically consists of 50 to 100 or more separate lines, each performing specific functions.
• The system bus is divided into three functional groups:
  • Data Bus
  • Address Bus
  • Control Bus

Functional Groups of a System Bus

1. Data Bus

   • Carries data between processor, memory, and I/O devices.
   • Consists of separate lines, possibly 8, 32, 64, 128, or more.
   • Bus width (number of lines) determines the amount of data transmitted at once.

2. Address Bus

   • Identifies specific locations in memory.
   • Unidirectional; indicates the source or destination of data.
   • The bus width determines the system's maximum memory capacity.
   • Example: A 16-bit address bus gives 64 Kilo address space.

3. Control Bus

   • Monitors and regulates data and address activities on the bus.
   • Controls timing information and signals indicating device status.
   • Holds control signals like memory read, memory write, I/O read, and I/O write.

Explanation of Bus Lines

• Data Bus: Bi-directional flow, width determines the amount of data.
  • Example: 8-bit width means 8 lines carry 1 bit each.
• Address Bus: Unidirectional, pointing to memory locations for data retrieval/storage.
• Control Bus: Bi-directional; carries control signals for operations like reads and writes.

Traditional Bus Architecture

• Processor connected to Cache via a local bus.
• Cache serves as a fast storage unit for executing tasks by the processor.
• System Bus connects main memory and interacts with expansion bus interfaces.
• Expansion Bus Interface allows additional devices to connect (e.g., network units, modems).
• Processor-mediated storage and retrieval through cache, system bus, and finally, main memory.

Key Takeaways

• Buses are critical for facilitating communication and data transmission between major system components.
• The system bus is an integral part of the computer's architecture, divided into data, address, and control buses to perform distinct roles.
• Understanding bus architecture helps in comprehending how different computer parts communicate and operate efficiently.