Jun 13, 2018 How to find CID of SD card windows. By Nikhil V S 4 replies Jun 11, 2018. Post New Reply. My pc has a built-in SD card reader, so I opened Computer and then inserted the SD card. (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. 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.