If I saved 1 byte of data on a USB drive, theoretically, would you be able to take apart the USB drive and point to where the 2nd bit of my single byte is? And if it is 0 or 1?
In: Technology
Theoretically, yes but you’d need a pretty powerful microscope.
The conversation about memory on a USB drive however is less about transistors, and more about how flash memory works. A transistor is just a type of circuit that is capable of being in one of two states . Depending on the design of the transistor depends on how it’ll be able to retain that state without electricity. In a flash drive, this is likely a floating gate design which is quite complex. But yes you could see what state it was in, thats kinda the whole point, that it will retain memory even unpowered.
USB drives use a technology called NAND Flash.
Individual transistors are only useful for one thing which is representing a position of On or Off, 1 or 0. They are the digital version of a light switch.
In order to do anything practical with them you have to combine multiple transistors and micro circuits into circuits called Logic Gates.
The basic ones are called AND, OR, and NOT. With more advanced ones being NAND, XOR, NOR, and several others.
Basically each gate takes in certain inputs and creates outputs based on their logic. For example AND only returns a positive result if both of it’s inputs are positive. This is useful for performing math equations.
A USB drive uses NAND flash which function like NAND gates but are able to store electrical current even when the power is cut.
Each NAND gate is in a state of either 0 or 1
To answer you other question, yes you can theoretically open a USB drive and look at it with a microscope and be able to identify the specific memory cells that contain any given bit of information.
Depends on the type of memory, but in most cases you would need to test it electrically.
For Nonvolatile memory (that is, memory that stays even without power), the main options are burning it to a disk with a laser or flash memory. Flash is what is used in USB drives and SSD card, and that uses something called a floating gate.
In a normal MOSFET transistor like those found in computer memory, you have the gate, the oxide separating it from the body, and then the source and drain (i.e. the two terminals of a transistor). When you apply a big enough voltage (or low enough, depending on the type of transistor) you effectively connect the two terminals via the oxide. A floating gate is a second layer between the gate and the body, and completely isolated such that it’s floating. When you program it (write to it) you draw charges in/out of that gate, to make it a 1 or a 0. Because it’s almost completely isolated (super high resistance material, but not infinite resistance), the charges stay in place and the device is locked into conducting or non-conducting.
For Random-Access Memory (RAM), normally a pair of NAND or NOR gates are connected together such that each’s output goes into the other as an input. This locks one side to be always 1 (as long as there’s power to the system) and the other side to be always 0, but which side is which can change (they just always have to be opposite each other, and the side you’re reading from doesn’t change). Changing that saved bit is then just a matter of flipping which side is 1 and which is 0, which you can do if you get the capacitances correct.
> And if it is 0 or 1?
Nobody seems to have answered this one yet: no you cannot see it. The NAND memory cell will look the very same to you, even under a very strong light-based microscope, regardless if it is 0 or 1. It will look silvery either way. You could measure its state electrically, though. As such, an electron microscope can show you the state because it reacts to the different electric charges.
A USB flash drive typically uses NAND storage, which is an array of cells, where each cell holds one bit of data. These are usually organised in blocks in a certain way, so if you’re familiar with the layout, you could figure out which cell holds the bit you want, and then probe it to check whether electric current flows through that cell, which tells you if it’s a 1 or a 0.
A cell is made out of a transistor, which is a sort of switch that only stays on for as long as you hold it. It’s like those public-bathroom sinks with auto-shutoff valves where you can only wash one hand at a time.
In flash storage, we *jam* that switch open to keep it from turning off automatically. Even when the power’s off, the switch stays in whatever position we last jammed it into. Then we add another switch that controls the jammer. Unfortunately this eventually breaks the valve and it typically gets stuck wherever we last put it, which is how SSDs wear out over time.
The “jamming” is putting an oxide wall around the gate of the transistor, so electrons can’t escape, and charging it up or discharging it *through* that wall using huge voltages and quantum tunnelling. So, in the sink-valve analogy, it’s a bit less like a wrench and more like a magnetic wizard.
Can anybody link me a video that can help emphasize this better ? I’ve always had this same thought , and I’m extremely curious
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