I built a Game Boy emulator in F#

I built a Game Boy emulator in F# Nick Kossolapov · April 2026

I’ve been working as a software engineer for over 8 years at this point, and admittedly I’ve never understood how computers actually work. So I figured I’d try to learn how they work by emulating one. Sorry Ben Eater, I’m not going to build one just yet.

I spent hundreds of hours as a kid catching Pokémon, so the Game Boy was the perfect candidate: real hardware, relatively simple in scope, and something with a strong personal connection.

Instead of jumping straight into it, I first did From NAND to Tetris. It was a great course, and it made me really understand the fundamentals of computers, like registers, memory, and the ALU. Then to get used to building an emulator, I built a CHIP-8 emulator in F#: Fip-8.

A few months later, and after many nights of going to bed at 2 AM even though I told myself I’d only work on it for an hour or two, I have a working Game Boy emulator: Fame Boy. Complete with sound and runs on desktop and web.

I wanted to have the emulator work on both desktop and web, so I focused on having a simple interface between the emulator core and whatever frontend is running it.

The interface between the frontends and core is essentially just two arrays and two functions:

framebuffer - a 160x144 array of shades (white, light, dark, black).

- a 160x144 array of shades (white, light, dark, black). audiobuffer - a ring audio buffer at sample rate of 32768 Hz with read and write heads.

- a ring audio buffer at sample rate of 32768 Hz with read and write heads. stepEmulator() - a function that executes one CPU instruction and returns the number of cycles taken.

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