Why Build a Computer from Scratch?
I wanted to understand how computers work at a very low level. By building an 8-bit computer, I would be able to see and visualize how all the parts of the computer link together. I got a kit from Ben Eater that walked me through how to build each module. He also explaned what each module did in detail.
What It Is
An 8-bit breadboard computer is a computer that processes data in 8-bit chunks. You set a value in Memory (RAM), and once it gets to a register, the ALU (which performs arithmetic) can add or subtract it. The result can then be output to a display.
The computer can:
- Send values to registers from the Memory module
- Perform addition and subtraction using the ALU
- Output results to a display
Key Components
Clock — A 555 timer circuit generates the clock signal. It can run in automatic mode or manual mode (single-step) for debugging.
Registers (A and B) — 8-bit registers that can store numbers up to 256
ALU (Arithmetic Logic Unit) — Can perform addition and subtraction on the values in registers A and B.
RAM — 16 bytes of static RAM. Programs are entered by hand using DIP switches
Control Logic — The heart of the machine. Decodes instruction and generates the control signals that coordinate all the other modules.
Output Register + Display — An 8-bit register connected to a display that shows the result.
Building It
Each module was built and tested independently before connecting them together. This is critical — debugging a complex system is much harder than debugging isolated modules.
The clock module came first since everything else depends on it. Then the registers, then the ALU, working through to the control logic last.
Wiring discipline matters enormously. I color-coded wires by function:
- Red: power (+5V)
- Black: ground
- Yellow: data bus
- Blue: control signals
- Green: clock
The entire build took several months of evenings and weekends, as I ran into a couple of tricky issues along the way.
Videos
What I Learned
This project gave me a deep understanding of how computers actually work at the hardware level — fetch-decode-execute cycles, how the ALU handles arithmetic, how control signals coordinate multiple modules, and what machine code really is.
It also made modern software feel like magic. The fact that the same fundamental logic — just vastly more complex and faster — runs everything from video games to AI models is genuinely mind-blowing once you understand the basics.
When the computer successfully added two numbers for the first time, it was one of the most satisfying moments I've had in any project. Every wire was placed with intention, and watching it work was incredible.