Developer Drew Breunig adapted the idea behind Divyansh Agrawal’s “qwenputer” to embed a working Nintendo Entertainment System (NES) 6502 CPU emulator into the weight space of the Qwen3.5-4B model. The demonstration is able to run NES ROMs such as Super Mario Bros — albeit very slowly.
How it was built
Breunig used Opus 5.5 prompts for the implementation and shared the prompts in a comment on Hacker News. For validation, the project relied on a conformance test collection for the NES CPU published roughly 15 years ago by Christopher Pow.
Starting from the qwenputer concept by Divyansh Agrawal, Breunig reorganized the Qwen3.5-4B model’s weights to represent the behavior of hardware components — in this case the 6502 CPU and memory. The objective was not performance optimization but to demonstrate that computational logic can be encoded inside a model’s internal representations and exposed via a command-line interface that accepts ROMs.
Capabilities and limitations
- The prototype produces a working emulator: NES ROMs can be launched through logic embedded in the model weights. The run speed is explicitly slow.
- The project is primarily experimental and educational, aiming to show that model weights can encode rule-based computation, rather than delivering a production-grade emulation solution.
Why this matters
The experiment illustrates that large language model weight space can be used to map complex, rule-driven computations beyond natural language representations. This opens new lines of inquiry into how model internals can implement nonstandard computation and how we might reason about such encodings.
Next steps and community invitation
Breunig suggested building the project further "just for fun": publishing the weight files and a CLI to run ROMs against them. He also noted that if smaller, faster models could be used with the same technique, it might be possible to approach standard NES clock speeds, although the current demonstration does not achieve that performance.
Where to find more details
Breunig published the used prompts in a Hacker News comment, and the work was inspired by Divyansh Agrawal’s qwenputer project. The testing relied on the conformance test suite for the NES CPU compiled by Christopher Pow about 15 years ago.
This is an experimental example of creative, nontraditional uses for generative models, presented without claims of production performance.
