How can a flash drive store information without power?



How can a flash drive store information without power?

In: Technology

From a very very simple standpoint, a flash drive stores data by flipping switches inside of the device. Off equals zero, on equals 1. Since all data is stored in zeros and ones, we don’t need any thing more complicated. Once the switches are set, the flash drive can be removed from whatever device, and put on the counter and the switches never move.

Same thing happens in your house. Lets say you are sitting at home and you have the light switch on in the kitchen, living room, and one of the bedrooms. The power goes out in your house. A few hours later, the power comes back on, and those lights turn back on. Why? it’s because those switches are still in the on position. They didn’t automatically turn off because the power went off.

Flash drives store data in tiny capacitors. If the capacitor is charged up, it’s a one and if not, it’s a zero. These tiny capacitors are not connected to a circuit to drain them, when the device is turned off, so they can hold their charge. Electrons are a physical thing, and if you squeeze a bunch of them into a tiny place and there is no way for them to get out, they have no choice but to just sit there.

A semiconductor memory chip is basically a tiny switchboard with many (several billion/trillions of) switches. Each switch stores one bit of data (1 or 0, on or off). Depending on how the switches are made, they can be stable in the on, off, or either position.

Bistable switches (like a light switch in your house) only need energy to change states (e.g. on to off), but not to remain in the same state. These are the type used in flash memory. Energy is only required to flip the switches, they remember what they were flipped to. We call this behavior non-volatile.

I’m contrast, semiconductor memory used in things like RAM use switches that are only stable in the off position. They need energy to remain on (similar to a doorbell switch). This is called volatile memory.

Because we don’t let the electrons move

RAM stores charge in capacitors, but capacitors leak charge over time. Its like a big grid of leaky cups on scales, heavy cups are 1’s and light cups are 0’s. There’s a task that goes around once in a while and tops up the mostly full cups and empties the mostly empty cups. If you lose power then that task doesn’t run and the charge (water) leaks out of the cups and you no longer have clear 1’s and 0’s

Flash memory used in flash drives and SSDs don’t store charge in capacitors, they instead ram electrons through insulators and onto “floating gates” of transistors to force those transistors on/off. Its like your cups of water were instead jello shots and if you wanted a 1 you rammed a bunch of steel ball bearings into it to make it heavier. The ball bearings have no way to drift out of the jello, they’re stuck in there so you don’t need a task going around to correct each cup on a regular basis

Basically we did a better job sticking electrons into a place where they can’t easily escape from so we lose data over years rather than seconds.