Lecture Notes on CPU and RAM

Introduction to CPU

• CPU (Central Processing Unit) is the brain of the computer.
• Understanding CPU operations provides insight into computer functions.

Inside the CPU: The 6502 Example

• The 6502 CPU was used in:
  • Apple II
  • Commodore 64
  • Original Nintendo Entertainment System (NES)
• Simulation available at visual6502.org.
• Clock: A critical wire that operates at a steady rate to synchronize operations.
  • 6502 clock: ~2 Hz.
  • Modern CPUs: Measured in GHz (billion Hz), operating in billions of cycles per second.

Scott CPU Overview

• Scott CPU: A conceptual design from the book "But How Do It Know" by John Scott.
  • Book available at buthowdoitknow.com.

CPU Components

Physical Structure

• Pins: Connect the CPU to the motherboard for data transfer.
• Motherboard: Connects all computer components.
• RAM (Random Access Memory): Holds data processed by the CPU.

RAM Interaction with CPU

• RAM operates with a list of addresses containing data.
• CPU processes data in order but can access RAM randomly.
• Enable Wire: Activates RAM to send data back to the CPU.
• Data in RAM: Composed of instructions, numbers, addresses, and letters (character codes).

Instruction Set of the CPU

• Instructions: Commands that tell the CPU to perform tasks (e.g., load, add, store, compare).
• Jump Instructions: Allow the CPU to change the sequence of operations based on conditions.

Example Program: Guessing Game

1. Load a number (e.g., 9) as the correct answer.
2. Retrieve user input from the keyboard.
3. Compare user input and the correct answer.
4. Jump to an instruction if the numbers match.
5. Output messages to the screen based on the user's guess.

Inside the CPU: Instruction Processing

Control Unit and ALU

• Control Unit: Manages instruction execution and coordinates components.
• ALU (Arithmetic Logic Unit): Performs mathematical operations (addition, subtraction, comparison).
  • Uses flags to report conditions (e.g., equality, greater than).

Registers and Memory Management

• Registers: Temporary storage for numbers during processing.
• Bus: Connects components for data transfer.
• Memory Address Register & Instruction Address Register: Manage RAM addresses for data requests.

Finalizing Instructions

1. Results from ALU operations are stored in registers.
2. Comparison results help determine the next instruction.
3. CPU retrieves and processes the next instruction from RAM.

External Interaction

• CPU communicates with external devices (monitor, keyboard) using specific instructions.
• Every port has an address for data transfer.

Data Storage: Hard Drive

• Hard Drive: Long-term data storage device, retains information when the computer is off.
• Data from the hard drive is loaded into RAM for processing.

Conclusion

• The lecture explored the fundamental workings of a computer's CPU and RAM.
• For deeper insights, reference the book "But How Do It Know" by John Scott.
• Notable quote: "Whatever you do, work at it with all your heart, as working for the Lord, not for human masters" - Colossians 3:23.