How does computer store everything which is saved even after switching off?
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I have a better understanding of solid state memory than hard drives, but hard drives act a lot like CDs and you already know, even if you dont necessarily understand that CDs dont lose their data when not powered. Solid state (Also called no volatile memory or NVM) storage what sits in an SSD, USD, or SD card, works with specially made transistors.
A transistor normally works because if you apply a voltage on the middle pin, it allows current to flow between the two outer pins. In more technical terms, the voltage at the collector is applied to the emitter, but only if the base is also powered. Waaaay long ago, they used a relay instead. The coil is literally a coil of wire that acts as an electromagnet, pulling two contacts together which allows current to flow through the contacts.
What can be done in transistors is isolate the base from the test of the circuitry. Normally, insulators don’t allow current to flow between two points. Air is a good insulator. But if the voltage is high enough, like between cloud and ground, the electrons will have enough energy to jump the gap and conduct. This happens on a nearly microscopic scale in modern NVM. The electrons jump the gap to the base and remain trapped there, permanently turning on the transistor. The state of the transistor is read by putting voltage at the collector and measuring whether it comes out of the emitter.
Clearing the memory cell works roughly in reverse, apply the opposite voltage, and let the electrons jump out. Very simplified, but enough for an ELI5 answer. The only thing I didn’t cover is the two main types of transistors are NPN and PNP. One of them turns on with a high voltage at the base and the other requires a low (or negative) voltage. Electrons being negatively charged require the latter to work in NVM.
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