Introduction

In March 2025, I signed up for the Coursera course From Nand to Tetris: Building a Modern Computer by Shimon Schocken and Noam Nisan. I thought “Why not learn how computers work from the basics?” Spoiler:- It’s not as easy as it sounds. The course promised to turn me into a computer-building wizard, and I got pretty far completing four out of six projects.

Logic Gates from NAND

The course starts with a simple idea: using only the elementary NAND gate, you can construct all other logic gates necessary for a modern computer. This concept blew my mind, the idea that complex systems ultimately reduce to this simple building block.

I started by implementing basic logic gates in the NAND2Tetris Hardware Simulator using hdl:

  • NOT gate
 CHIP Not {
    IN in;
    OUT out;

    PARTS:
    Nand (a = in, b = in, out = out);
 }
  • AND gate
CHIP And {
    IN a, b;
    OUT out;

    PARTS:
    Nand (a = a, b = b, out = aNandb);
    Not (in = aNandb, out = out);
}
  • OR gate
CHIP Or {
    IN a, b;
    OUT out;

    PARTS:
    Not (in = a, out = nota);
    Not (in = b, out = notb);
    And (a = nota, b = notb, out = and);
    Not (in = and, out = out);
}
  • XOR gate
CHIP Xor {
    IN a, b;
    OUT out;

    PARTS:
    Not (in = a, out = nota);
    Not (in = b, out = notb);
    And (a = a, b = notb, out = temp1);
    And (a = nota, b = b, out = temp2);
    Or (a = temp1, b = temp2, out = out);
}

Pro Tip: Use NAND Game! to understand how theses gates are formed using NAND.

As It transforms theoretical concepts into visuals that make implementation much easier than it seems.

From Gates to Chips

Once I had a grip on basic gates, it was time to get serious and build some chips. Enter the realm of multiplexers and demultiplexers. These allow you to:

  • MUX (Multiplexer): Choose which input signal to use.
  • DMUX (Demultiplexer): Route signals to different outputs based on selection bits.

I thought the difficulty would skyrocket when I started with the 16-bit and multi-way chips, but once I built the first 16-bit chip, the rest were a breeze, just a bit of grunt work, really.

Arithmetic Components

Next came the exciting part which is creating chips that can actually compute! I implemented:

  • Half Adder (adding two bits)
  • Full Adder (adding three bits with carry)
  • Multi-bit Adder (for 16-bit )
  • The ALU (Arithmetic Logic Unit)

From Bits to Storage

The next phase took me into the realm of computer memory, where I designed:

  • Registers: Flip-flop based storage units that hold data temporarily
  • RAM8: A small 8-register memory unit
  • RAM64: A memory unit of 64-register
  • RAM512, RAM4K, and RAM16K: Increasing memory units
  • Program Counter (PC)

This hierarchy of memory components taught me how computers are organized.

Challenges and Limitations

While I successfully completed four projects, the two modules focused on assembly language programming were… let’s just say, less successful. I realized I’m a visual learner who prefers tools like simulators. Still, the struggle was part of the fun—sort of.

Resources That Helped Me

  • The NAND game (seriously, don’t skip it!)
  • Course forums where students swapped war stories about their challenges (misery loves company).
  • Drawing chips designs on paper before implementation

Conclusion

While I didn’t complete all six projects, the four I finished gave me a solid foundation in computer architecture that I’ll build upon.

If you’re curious about how computers really work from the ground up, I highly recommend this course. It’s tough, but incredibly rewarding. After all, who wouldn’t want to say, “I built a computer from scratch with just a NAND gate”?