Maker Will Whang has designed and open sourced an MK4001MTD USB Bridge, a USB mass storage compatible device which facilitates the use of the world's smallest mechanical hard drives with modern tech. For two decades, thousands of these tiny storage devices have sat in drawers and shelves, their data effectively trapped and inaccessible to anyone with modern computing equipment.
Toshiba launched its 0.85-inch MK4001MTD hard drives in 2004, offering an attractive balance of capacity and pricing, but as they were sidelined quite rapidly due to the advance of flash memory tech, not many device designs adopted them. This has led to these tiny HDDs, and the data upon them, basically getting lost in time.
The challenge proved genuinely difficult. Whang explains that several prior attempts had been made at accessing the obsolete MK4001MTD drives, but they had fallen at various hurdles. Starting with the basics, Whang compared drives and reader interface pads that looked similar to the MK4001MTD—looking somewhat like an SD card with an MMC-style connector—so various old spare readers were used with the Toshiba drives to see what happened.
Early assumptions proved incorrect. Whang eventually decided to build their own reader based around the USB2240 flash media controller chip, making it possible to use a logic analyzer to see what signals were going where, but it became clear that "this was not behaving like a normal SD or MMC storage device," so more analysis would be necessary, which would extend all the way into a reverse engineering effort.
A critical breakthrough came from an unexpected source. For the next stage of the project, Whang acquired a beaten-up but usable Nokia N91, a mobile device that was one of the rare MK4001MTD adopters back in the mid-noughties. After getting the old phone to boot so they could capture the traces, the purpose of each pad became much clearer. This insider perspective from an actual device that used the drives proved invaluable in understanding the protocol.
With the software, firmware, and interface design finalised, Whang designed a custom PCB for a neat, professional-looking solution using KiCad, sharing the design language of their prior 1-inch MicroDrive project. All the source code, hardware design files, and more have been shared on GitHub under the most liberal "I do not care" licence.
The practical result offers access at a trade-off. USB access to the MK4001MTD works reliably but is a pedestrian 0.42 MB per second read and write speed at best, with the SDIO clock set to 10 MHz; the Toshiba drive was a measly 4GB, but at such a slow transfer speed, it would take about two and a half hours to read a full HDD or write it to full. Yet for anyone holding onto one of these devices with irreplaceable files, the speed limitation becomes irrelevant compared to the prior alternative: complete inaccessibility.
This project exemplifies a wider concern in computing: obsolescence planning. Devices continue to accumulate in homes and offices around the world, and manufacturers rarely provide pathways for data recovery once production ends. Whang's open-source solution demonstrates that motivated individuals can solve problems the market no longer considers worth solving, often providing the best solution available.