Reading around they seem work in the same way and appear the same within Linux. I’m not well enough versed on the technology to know quite what the difference between eMMC and SD cards are, aside from the way SD cards are packaged of course – although that might be all there is to it. In that presentation was mention of vendor commands for a Samsung eMMC used as the built-in storage on an Android phone. If you’ve found this page by looking for help on this topic you’ve probably already seen Bunnie Huang’s SD card hacking presentation, unfortunately I wasn’t able to track down any APPO AX211 based cards, which I thought would be my best bet. However, there is probably some way to unlock them… All the cards I got seemed to honour that restriction. The spec includes a command (CMD26) for writing the CID, but it’s only supposed to work once in the factory when the card is first assigned an ID. There are rumours of cheap Chinese SD cards that don’t follow the official spec and allow you to change to them – I now have large pile of cheap Chinese SD cards on my desk, but unfortunately none of them did allow it. For example, if you want to change the supposedly read-only ID on various kinds of RFID tag you can simply buy a special version from China that allows it (often referred to as gold or magic cards). There is surprisingly little info out there about this, when it’s easy for other devices.

I’ve spent a while trying to work out how to change the ID on some cards. This can result in you being stuck with a smaller card than you’d like in a device or not being able to use a backup in case of damage.

(tl dr – skip to bottom for instructions, see also update post) The CID register on SD cards is supposed to be read-only, which means it can be used to lock devices to specific SD cards, preventing the user swapping them out, which is very annoying.

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