Building a Reader for the Smallest Hard Drive

2 days ago

Toshiba introduced the MK4001MTD, a 0.85-inch hard disk drive in 2004, recognized by Guinness World Records as the world's smallest HDD.
The drive was used in products like the Nokia N91, offering 4GB storage before flash memory became more practical.
Initial attempts to read the drive using standard SD/MMC readers failed, leading to reverse engineering efforts.
A Nokia N91 was used to probe the drive's signals, revealing it uses a 4-bit SD/MMC interface with SDIO protocol.
OpenClaw, an LLM, helped reverse-engineer the logic traces and develop firmware for the RP2040 to interface with the drive.
The final design includes a custom board with spring-loaded contacts for the drive, achieving a functional but slow read speed of 10 MHz.
All project files, including firmware and hardware designs, are available on GitHub for further study and modification.

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