system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How exactly is data electronically stored on tiny devices like Micro SD cards?
gpt
Flash memory is stored in little devices called floating gate transistors. 


Transistors are the little electrical switches that computers use to process things and amplifiers use to amplify signals. They have three terminals, a source, drain, and gate. The voltage applied to the gate controls whether current can flow from the source to drain, the gate is the switch. A high voltage opens or turns on the transistor, this is what computers use as binary "1". No voltage closes or turns off the transistor, this is a binary "0". All digital data is stored as 1s amd 0s, and computers process it as 1s and 0s using these transistor switches. As you can tell here, the switches work great for running a computer or even sitting data in the computers RAM, but to stay on or open they need a voltage, so the second you remove the power the voltage disappears and any data is lost. 


A floating gate transistors works the same way, but the gate is highly insulated. Electrons that get into it get stuck, and hence the voltage can be held when the power is removed. Any transistors trapping electrons are left open holding a 1, while any without trapped electrons are left closed holding a 0. This allows flash memory to store data without power. To get the electrons through the insulation and get trapped in the first place, a really high voltage (computer high, not powerline high) is "flashed" to groups of transistors, hence **flash** memory. 


A microSD card has billions of these transistors, and their sizes range in the nanometres (nm). A piece of paper has a  thickness of 0.1mm, that's thin but still 100,000 nm. Transistors have measurements on the order of about 100-10nm. When a microSD card has 64 GB, that means it has somewhere around 500 billion transistors in it.