Understanding the CPU and RAM Interaction

Overview of the CPU

• CPU: Central Processing Unit; considered the brain of the computer.
• 6502 CPU: Historically used in Apple II, Commodore 64, and Nintendo Entertainment System.

Key Features of CPUs

• Clock Wire:
  • Turns on/off to keep components in sync.
  • Modern CPUs operate at gigahertz (billions of cycles per second).
• Manufacturers: Intel, AMD, etc.

Introduction to the Scott CPU

• Scott CPU:
  • A design from the book "But How Do It Know" by John Scott.
  • Recommended for understanding CPU components without technical jargon.

Components of the CPU

• Pins: Connects the CPU to the motherboard for data transfer.
• Motherboard: Allows connection between various components.

Understanding RAM

• RAM: Random Access Memory, stores data being processed by the CPU.

Interaction between CPU and RAM

• Data Retrieval: CPU pulls data from RAM based on addresses.
• ENABLE Wire:
  • Must be activated for RAM to send data to the CPU.

Data Types in RAM

• Instructions: Tell the CPU what operations to perform.
• Numbers: Can be processed mathematically.
• Addresses: Point to other data locations.
• Letters: Stored as 1s and 0s based on character codes.

Instruction Set of the CPU

• Basic Instructions:
  • Load: Transfer number from RAM to CPU.
  • Add: Perform addition on two numbers.
  • Store: Save results back to RAM.
  • Compare: Compare two numbers.
  • Jump-If: Conditional jump based on comparison results.
  • IN/OUT: Input from devices or output to devices.

Example Program: Guessing Game

1. Load a predefined number (e.g., 9).
2. IN instruction retrieves user’s guess.
3. Compare guess with the predefined number.
4. Jump-If Equal to show feedback.

Inside the CPU: Data Processing

• Control Unit: Directs the CPU's actions based on instructions.
• Arithmetic Logic Unit (ALU): Performs mathematical operations.
• Registers: Temporary storage for quick data access.
• Flags: Indicators that help in decision making.

Data Flow within the CPU

• Bus: Group of wires connecting components.
• Memory Address Register: Holds the address for the next instruction to retrieve from RAM.

Final Assembly of the Computer

• Output Devices: Monitors and keyboards connected via ports.
• Hard Drive: Permanent storage, data moved to RAM for processing.

Conclusion

• Understanding this basic structure allows comprehension of more advanced CPUs.
• For detailed understanding, refer to John Scott's book and website buthowdoitknow.com.