Why are USB memory sticks also called flash drives?
Because the storage technology behind it is called flash memory. If you’re wondering what that means I can’t promise that you will be smarter at the end of this article. But what I can do is give you some textual and visual ideas. Latter is what I always find to be most helpful.
So at first a brief text definition. Flash memory is a type of EEPROM which stands for Electrically Erasable Programmable Read-Only Memory. It’s a non-volatile memory that can store little data chunks especially when there’s no power. When the chunks need to be larger the specific flash kind is used. In other words, usual EEPROM is only byte-erasable whereas Flash is block-erasable. I’m sure you already feel smarter or lost.
Ok, then let’s have a picture that shows the typical interior of a USB flash drive.
What you see on the left is the chip that holds the actual flash memory and the chip on the right is called a microcontroller. The last part is just for your information and shall be of no interest regarding flash technology. So keeping focused on the left chip, inside it is an array of memory cells which themselves contain floating gate transistors. You can see one in the next image:
Source: ZDNet defintion for EEPROM
To quote above source, “The storage part of an EEPROM cell acts like a permanently-open or closed transistor. Charging is accomplished by grounding the source and drain terminals and placing a voltage on the control gate. When the “floating gate” is charged, it impedes the flow of electrons from the control gate to the silicon, and the 0 or 1 is determined by whether the voltage on the control gate is blocked or not.”
Uhm, ok. Now, 0 means a transistor is off and 1 means it’s on because the gate is open and electricity can flow. With a regular transistor the data would be lost once the power is turned off because that shuts down the whole thing and it stays in the 0 position even when power is back on. A flash memory cell however saves the data because it’s basically in a permanent 1 position. That’s due to its second gate, the floating gate, which enables electricity to stay trapped between it and the first gate. The data can still be erased though by draining the electricity out, that’s what the drain to the right is for.
I guess I could try to get into more detail now but to be honest, I really don’t understand most of this stuff. I just use these sticks and think they’re cool. What I’m left wondering is: Why is it actually called Flash? Is it just some fancy marketing phrase? Either way, if you want to get deeper and feel this urge to also know what a microcontroller is for I advise you to join a geek forum or sift through the tons of articles out there on the net. Then please come back and post an explanation.
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