These are my personal notes on CPU registers, computer memory, and assembly basics, taken while learning through Pwn.College.

I found these topics challenging at first, so I wrote down every question that came to mind — it helped me understand the concepts more deeply and retain them better.

Understanding how the CPU and memory work is especially beneficial when it comes to cybersecurity, reverse engineering, and low-level debugging.

📌 Note: A bit of background in assembly or systems is helpful —

so try to use these notes alongside a computer architecture course for best results.

🧠 Overview: The Instruction Cycle (a.k.a. Fetch–Decode–Execute cycle)

This is the core process the CPU uses to run a program.

🔁

1. Fetch

(from RAM to CPU)

• The Control Unit (CU) sends the address of the next instruction to RAM.
• That instruction is fetched from RAM into the Instruction Register (IR) inside the CPU.

➡️ Instruction is now inside the CPU, ready to be processed.

🧠

2. Decode

(by Control Unit)

• The Control Unit decodes the instruction: What operation? What data? What registers?
• It identifies:
  • The operation (e.g., ADD, SUB)
  • The operands (data or register names)
  • The destination (where to store the result)

➡️ The CU sends signals to the ALU and registers to prepare.