Hobbyist uses Xiaolongxia (小龙虾 AI) to resurrect world’s smallest mechanical hard drive from a Nokia N91

What happened

A hardware enthusiast has reportedly used a Chinese open-source AI agent, Xiaolongxia (小龙虾 AI, also known as OpenClaw), to help decode and reverse-engineer the Toshiba MK4001MTD — a 0.85‑inch, 4GB micro mechanical hard drive first released in 2004 and long out of production. It has been reported that Will Whang captured low‑level signals from a mid‑2000s Nokia N91 phone to establish that the drive speaks a 4‑bit SDIO interface that nevertheless transports ATA‑style device identification commands, and then built a bespoke USB bridge to make the tiny disk appear as a standard USB storage device.

How it was done

Whang initially tried conventional SD/MMC readers and failed. So he harvested a working N91 to probe the motherboard pins and trace the protocol. After mapping the hardware logic, he reportedly turned to Xiaolongxia to tackle the software layer: the AI helped decode the complex SDIO signalling, generate an SDIO decoder and even produce low‑level firmware for a Raspberry Pi Pico. He later used additional tools — Opus 4.6 and, reportedly, a GPT‑5.4 large model — to further refine the code before validating the reader on a breadboard.

Results and limits

The project culminated in a professional PCB drawn in KiCad to match the look of Whang’s earlier 1‑inch HDD project, and all source code, firmware and hardware schematics have been uploaded to GitHub under a permissive open‑source licence. Performance is limited by the original mechanics and interface: at a 10 MHz SDIO clock the drive tops out around 0.42 MB/s, meaning a full 4GB read/write cycle takes roughly two and a half hours.

Why it matters

Why should Western readers care? This is a clear example of how modern AI tools — including open‑source Chinese models and large LLMs — are accelerating retrocomputing and hardware reverse engineering, enabling enthusiasts to bridge decades‑old interfaces. It also underscores practical issues raised by shifting supply chains and export controls: when manufacturers discontinue niche parts, community projects and open designs become crucial for data recovery and device preservation.