How I built a web based CPU Simulator

As someone passionate about computer engineering, reverse engineering, and system internals, I've always been fascinated by what happens "under the hood" of a computer. This curiosity led me to develop a CPU simulator—a web-based project designed to visualize the internal workings of a CPU, from register operations to memory manipulations, similar to how tools like GDB work in a Linux environment.

In this blog post, I’ll walk you through the motivation, features, architecture, and potential use cases of my CPU simulator project.

https://cpusimulator.org

Why a web based simulator? Isn't GDB Enough?

During my studies and exploration in reverse engineering, penetration testing, and low-level programming, I found that many learners struggle to understand how a CPU actually processes instructions. Most theoretical resources are abstract, and while tools like GDB and IDA Pro are powerful, they can be overwhelming for beginners.

So I thought—what if I could build an interactive, visual, and beginner-friendly tool that simulates how a CPU executes assembly instructions step-by-step?

That’s where the idea was born.

What the Simulator Does

My CPU simulator is designed to mimic the operation of a simplified Intel x64 architecture. Here are some core features:

• Instruction Parsing
  The simulator can parse and execute x86 assembly instructions such as MOV, PUSH, POP, ADD, SUB, JMP, and more. It supports both register-to-register, register-to-memory, and immediate value operations.

• Register Simulation
  It simulates general-purpose registers like RAX, RBX, RCX, etc. The user can view register values in real time as instructions are executed.

• Memory Viewer
  The memory component allows users to visualize memory content similar to how GDB displays it. Each memory block shows:

  • Address
  • Byte-level breakdown
  • Full word (e.g., 64-bit) in hex

• Instruction Flow Control
  Users can step through each instruction, watch how the CPU state changes, and debug their assembly-like programs interactively.

• Operand Handling
  The parser supports a variety of operand types:

  • Immediate values (e.g., MOV RAX, 0x10)
  • Registers (e.g., MOV RAX, RBX)
  • Memory references (e.g., MOV RAX, [0x200])

• Stack Behavior
  It models stack operations, including PUSH and POP, updating the stack pointer and memory layout accordingly.

Built with React.js

You might wonder why I used React.js—a frontend framework—rather than a lower-level language like C or C++. The reason is simple: visualization and accessibility.

• React’s component-based model made it easy to modularize elements like the memory viewer, instruction editor, and register display.
• The entire simulation runs in the browser—no installation required.
• JavaScript’s dynamic nature made it easier to quickly iterate on instruction parsing and UI responsiveness.

While JavaScript is not optimal for performance-heavy tasks, for educational purposes and visualization, it's a great fit.

Who Is This For?

This project serves a variety of audiences:

• Students learning computer architecture
  See how each instruction impacts the CPU state in real time.

• Reverse engineering enthusiasts
  Visualize how stack and memory manipulation work at the assembly level.

• Security researchers
  Understand memory vulnerabilities like buffer overflows and how shellcode operates at a low level.

• Educators
  Use the simulator as a teaching aid to explain CPU internals in a visual and interactive manner.

Future Enhancements

I'm actively working on improving this project. Some upcoming features include:

• Support for more instructions (e.g., CALL, RET, conditional jumps)
• Assembly editor with syntax highlighting
• Breakpoints and watch variables
• Improved memory inspection tools
• Integration with tutorials for learning assembly programming

Open Source

Yes—this project is open source! I believe in the power of community collaboration. If you're interested in contributing, testing, or even just playing around with it, you’re welcome to check it out on GitHub.

🔗 https://github.com/thil4n/cpu-simulator

Final Thoughts

Building this CPU simulator has been one of the most rewarding projects I’ve undertaken. Not only has it deepened my own understanding of low-level computing, but it has also helped others visualize and grasp the fundamentals of CPU behavior.

If you're a student, educator, or just a curious hacker—give it a try. And if you have feedback or want to collaborate, feel free to reach out!

Thanks for reading!
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