How do USB Flash Drives store information?


How do USB Flash Drives store information?

In: Technology

Each bit is stored in a MOSFET transistor. A transistor have three terminals. A source and drain for the current and a gate which controls if the transistor will allow current through or block the current. So be charging or discharging the gate we can controll if a signal is allowed to pass through the transistor. But in flash memory we do not want to accidentally have the charge leak out of the gate as we can not constantly be charging up the gate when you unplug it. So we make sure the gate is isoletad from all electrical connections. This does however pose the problem of how you can charge and discharge it to set its value. The solution is literally quantum physics. By manipulating the charges in the transistor and in an additional gate on the transistor using very high voltage you are able to quantum tunnel electrons through the insulating material to charge or discharge the gate.

Basically every cool thing is built around transistors which are little electronic switches

Your Flash drive has a chip with billions of these little switches

When we go to store data we ram electrons into the gate of these little switches which gets them stuck in an on or off state. The little electrons are trapped in an insulator and can’t go anywhere when power is removed

When you go to read your file back, the controller goes through and checks the state of the switches, on is 1 and off is 0, and then it reports all those bits to your computer.

We’ve made denser ones by having switches that we can turn kinda on to store more than one bit per switch and then check how on the switch is when you read from it

Imagine you have 3 dices and you want to remember a 3 digit number 156. You can leave the dice face in order to store that information and to store a different number you can simply change the face of the dice.

Inside the flash drives, we managed to squeeze billions of such dices, and hence flash drives can store much more information.

Switches, like all computers it’s down to switches, on an empty flash chip all the switches are off (in binary that’s 0) when you write data to it some of the switches turn on others turn off so to store the letter A 8 switches will be assigned values 01100001 8 switch commands is called a byte. large data may be in the mega or giga byte range and take up a large amount of allocated switches.

A flash drive only has a set amount of switches so it can only allocate a fixed amount, when all the switches are allocated the drive is full.

They have tiny bits of silicon surrounded by insulators called cells. When a flash drive writes information, it turns on the cell it wants to write to (by using electronic switches called transistors) and zaps the cell with electricity. Normally electricity can’t go through insulators, but with high enough voltage you can force it to quantum tunnel (a bit beyond ELI5 range). Think of it as lightning, normally air is an insulator but lightning is high enough voltage to go through it anyways.

To read the cell, it turns on that cell using the transistor switches and runs a current near the trapped silicon cell. If the cell contains electricity from having been previously zapped, it will affect the current, which your computer can measure and determine whether the data stored in that cell is a 1 or a 0.

To make it more complicated, we’ve gotten more precise with how we zap the cells so that we can store more than just a 1 or a 0 in it. We can store any value from 0-7 in a single cell, and the reading process will be able to tell exactly how much electricity is store inside the cell to figure out which value from 0-7 is stored in it.