Enthusiast breaks into smallest HDD with only phone and OpenClaw
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Enthusiast reverse engineers world’s smallest HDD to access data with help from an old Nokia N91 and OpenClaw — open source USB bridge unlocks 0.85-inch mechanical Toshiba drive from 2004 | Tom's Hardware Skip to main content Don't miss these Storage Microscopes can clearly see the video on the surface of a CED 'LaserDisc,' discovers Techtuber Retro Gaming 385TB video game archive saved by fans — Myrient has been '100% backed up' and validated, torrents being generated Macbooks Apple's MacBook Neo modded to a 1 TB SSD, breaking the firm's 512 GB barrier USB Flash Drives Unpowered flash drive data retention test shows promising results after six years NAS Minisforum's new flagship NAS comes with OpenClaw pre-installed PC Building Classic tiny LEGO computer brick design from 1979 made into full-scale working computer — Mac Mini implanted into this 10:1 scale inflated reimagining HDDs Best Hard Drives 2026: The best HDDs for desktop PCs, NAS, and more, based on our extensive benchmarking External SSDs How to protect yourself from bad external SSDs during the PC hardware apocalypse Retro Gaming ‘Mad scientist’ visualizes Atari 2600 fetching data from ROM for mesmerizing light show Storage Microsoft's Project Silica write-once storage could store terabytes of data for over 10,000 years HDDs Seagate begins shipping 44TB hard drives with HAMR tech to data centers HDDs Western Digital is already sold out of hard drives for all of 2026 SSDs SATA SSD cheated death from failed attempt at data destruction with a drill Storage Developer turns floppy disks into secret black-and-white picture canvases USB Flash Drives Researcher builds bizarre 128-byte USB drive the size of a dinner plate using ancient pre-semiconductor magnetic core memory technology (Image credit: Will Whang ) Copy link Facebook X Whatsapp Reddit Pinterest Flipboard Email Share this article 0 Join the conversation Follow us Add us as a preferred source on Google Newsletter Tom's Hardware Get the Tom's Hardware Newsletter Get Tom's Hardware's best news and in-depth reviews, straight to your inbox. Contact me with news and offers from other Future brands Receive email from us on behalf of our trusted partners or sponsors By submitting your information you agree to the Terms & Conditions and Privacy Policy and are aged 16 or over. You are now subscribed Your newsletter sign-up was successful An account already exists for this email address, please log in. Subscribe to our newsletter Maker Will Whang has designed and open sourced an MK4001MTD USB Bridge . This is a USB mass storage compatible device which facilitates the use of the world’s smallest mechanical hard drives (obsolete for many years) with modern tech. MK4001MTD reading test - Windows XP and macOS - YouTube Watch On Toshiba launched its 0.85-inch MK4001MTD hard drives in 2004, offering an attractive-at-the -time balance of capacity and pricing. However, 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. Whang explains that several prior attempts had been made at accessing the obsolete MK4001MTD drives, but they had fallen at various hurdles. So, the maker decided to start collecting working (and non-working) units to see if they could crack this particular old storage nut. Article continues below You may like ATABoy bridges old IDE drives to the 21st century with Open Source USB host bridge Open source IDE-ATAPI drive emulator launches for vintage computers Researcher builds bizarre 128-byte USB drive the size of a dinner plate using ancient pre-semiconductor magnetic core memory technology Starting with the basics, Whang compared drives and reader interface pads that looked similar to the MK4001MTD. Yes, it looks 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. Eventually, Whang decided to build their own reader based around the USB2240 flash media controller chip. It thus became possible to use a logic analyzer to see what signals were going where. (Image credit: Will Whang ) Unfortunately, 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. For this next stage of the project, Whang acquired a beaten-up but usable Nokia N91. This mobile device was one of the rare MK4001MTD adopters back in the mid-noughties. (Image credit: Will Whang ) After getting the old phone to boot, so they could capture the traces, the purpose of each pad became much clearer. “The traces confirms this is a 4-bit SD/MMC interface and N91 service manual pin connection is indeed correct. The bus activity showed CMD52 traffic, which immediately pointed toward SDIO rather than a normal memory-card mode,” says Whang. “Looking further into the command contents, it also appeared that ATA-style commands such as IDENTIFY DEVICE were being transported over that interface.” Stay On the Cutting Edge: Get the Tom's Hardware Newsletter Get Tom's Hardware's best news and in-depth reviews, straight to your inbox. Contact me with news and offers from other Future brands Receive email from us on behalf of our trusted partners or sponsors With the rough idea about what was going on, the maker decided to leverage OpenClaw to look after the software side of a USB reader solution. The AI agent was broadly successful, notes Whang, as it “successfully reverse-engineered the logic traces by building its own SDIO decoder, then wrote firmware for the Pico that exposes the drive as USB mass storage.” Encouraged by the OpenClaw success, Whang decided to turn to Oups 4.6 and later GPT-5.4 for an improved result, which worked with their breadboarded Pico and a hand-wired drive. (Image credit: Will Whang ) Hardware design stage Now happy with the software, firmware, and interface design, Whang decided to fire up KiCad and design a custom PCB for a neat, professional-looking solution. It shares the design language of the maker’s prior 1-inch MicroDrive project. (Image credit: Will Whang ) The result is that USB access to the MK4001MTD works reliably but is a pedestrian 0.42 MB per second read/write speed, at best, with the SDIO clock set to 10 MHz. This Toshiba drive was a measly 4GB (less than a DVD capacity), 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. Whang concludes that they are happy with the collaborative work with a reasoning-focused LLM, and future projects might follow a similar structure. All the source code, hardware design files, and more have been shared on GitHub under the most liberal “I don’t care” license. Follow Tom's Hardware on Google News , or add us as a preferred source , to get our latest news, analysis, & reviews in your feeds. TOPICS See all comments (0) Mark Tyson News Editor Mark Tyson is a news editor at Tom's Hardware. He enjoys covering the full breadth of PC tech; from business and semiconductor design to products approaching the edge of reason. 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