Building a Computer from Scratch — Part 1: Wires and Logic Gates
Every computer is built from wires and gates. This post starts from scratch — what is a wire, what is a gate, and why one small design decision here is...
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Building a Computer from Scratch
An 18-part series building a complete 16-bit computer from first principles in Go, based on the book But How Do It Know? by J. Clark Scott. Starting from a single wire and NAND gate, we build upward through storage primitives, the bus, arithmetic, registers, the ALU, 64K RAM, I/O, a CPU, and finally an assembler that runs real programs.
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Building a Computer from Scratch — Part 2: Multi-Input Gates
Extending the gate layer to handle three, four, five, and eight inputs at once — and why the struct fields matter more than the truth table.
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Building a Computer from Scratch — Part 3: Storage Primitives
Building the first component that can remember — a 4-NAND feedback loop that locks a bit in place, and why Go's zero values make it tricky.
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Building a Computer from Scratch — Part 4: The Bus
Storage cells can hold values, but they can't talk to each other. This phase builds the shared channel that every component in the computer will use to pass data.
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Building a Computer from Scratch — Part 5: Enabler & Bitwise Ops
Building the gate that silences a component on the shared bus, and discovering that a left shift is just rewiring — no logic required.
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Building a Computer from Scratch — Part 6: Comparison & BusOne
Building the comparator that chains 16 bit-stages MSB-first, and BusOne — the gate that injects the constant 1 without an if-statement.
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Building a Computer from Scratch — Part 7: Decoders
One NOT per input, not one per gate — and how cascading two 4×16 decoders selects any one of 256 outputs without 8-input AND gates.
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Building a Computer from Scratch — Part 8: The Adder
Building a 16-bit ripple-carry adder from five gates per bit column.
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Building a Computer from Scratch — Part 9: The Register
Combining storage and bus access into a single unit with two independent control wires.
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Building a Computer from Scratch — Part 10: The Stepper
Building a six-position shift register that gives the machine a shared sense of time.
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Building a Computer from Scratch — Part 11: The ALU
Assembling eight parallel operation units behind a decoder-controlled gate, so a 3-bit opcode routes exactly one result onto the bus — with no branching in sight.
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Building a Computer from Scratch — Part 12: Memory (64K RAM)
Building 65,536 cells in a 256×256 grid, selected by two 8-bit decoders, with a Memory Address Register that makes the two-phase read/write protocol possible.
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Building a Computer from Scratch — Part 13: I/O Bus & Keyboard
Adding a 4-wire I/O control bus to keep RAM silent during peripheral cycles, and a keyboard that detects its own address in pure gate logic and delivers keycodes across a...
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Building a Computer from Scratch — Part 14: Display
Adding a 4,800-cell frame buffer with two independent address registers, a two-phase write protocol, and a 30fps scanner goroutine that never touches the CPU's bus.
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Building a Computer from Scratch — Part 15: The CPU
Wiring nine registers, a stepper, an ALU, and a control unit into a fetch-decode-execute machine that runs one instruction every six clock steps.
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Building a Computer from Scratch — Part 16: The Complete Computer
Connecting CPU, RAM, keyboard, and display into a single runnable machine — with a memory map, a sentinel jump, and a clock loop.
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Building a Computer from Scratch — Part 17: The Assembler
After 16 phases of hardware, the computer can run programs — but only if you write them in raw binary. This final part adds an assembler that translates human-readable instructions...
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Building a Computer from Scratch — Part 18: Putting It All Together
The three pieces that turn Go packages into a running simulator: a program generator that writes assembly from code, a bug that only appeared end-to-end, and a three-goroutine simulator that...