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Flash drives are small devices that allow people to store information. These external “memory” tools for our computers are much more complex than they appear. In this article, we’ll try to answer some of the questions that are usually associated with flash drives.
How do flash drives store information?
Flash drives store information in ones and zeros. They use an electrical process, known as flash memory, to store the data in bytes. If you aren’t familiar with flash memory, let me try to explain it. In simple terms, flash memory consists of a source, a drain, a floating gate, and a control gate. The floating gate is capable of storing electrons. In fact, when no information is stored, the cell is holding electrons. Before I further describe the process, it might be helpful to visualize the organization of these components.
When trying to store a ‘0’ in place of a ‘1’, a positive charge can be added to the worldline and bitline. This will cause the electrons to rush to drain even though it is separated by an electron-deficient material. Some electrons will also make their way through the oxide layer (in blue below the floating gate) and be trapped in the floating gate. Once trapped there, the electrons will remain in the floating gate for many years to come, even if there is a current flow between the source and the drain. To erase the information and restore the transistor, a negative charge can be added to the worldline to repel the electrons stored in the floating gate. Doing so would store a ‘1’. When a flash drive is empty, the flash memory cells all store a '0'.
When will my USB drive no longer work?
The USB drive wears out every time you write and rewrite information. Basically, every time you trap electrons and repel electrons from the floating gate, you make it harder to switch between the two options in the future. Eventually, changing the information is no longer possible because the flash cell has completely worn out.
How does a USB drive read the information it has stored?
When trying to access the information, a low voltage is applied to the worldline and bitline. If the cell is storing a logic ‘1’, a current will be created and measured exiting the bitline. However, if it is storing a ‘0’ and electrons are present in the floating cell, the voltage threshold of the flash cell is higher than the voltage applied. This means that no current will be measured leaving the bitline. A current sensor is placed after the bitline to determine whether or not there is a current flow and share that information with the computer so that it may interpret it as ‘1’s and ‘0’s.
How are these flash cells positioned?
Flash memory cells can be single-layered, as explained above, or multi-layered. A single-layered cell stores one Bit of information, while multiple layered cells store more information. Interestingly enough, the size of the multilayered cells is approximately the same as the single-layered cells. This means that having multiple layers allows for more storage space and decreases the price per Bit. Unfortunately, the more layers present, the longer it takes to read the information. Then, the flash memory cells are juxtaposed into pages. Pages are juxtaposed into blocks, which are juxtaposed into planes. In a die, there are usually one or more planes. The die is then placed on a circuit board and voila, the USB flash drive’s main component is created.
What does USB stand for?
USB stands for universal serial bus. The fact that it is bus-powered means that it does not require an external power source because it takes the power from the connection and doesn’t need power when it is not connected.
Can I leave my USB drive plugged in?
It is better to avoid leaving it plugged in because leaving the low voltage current all the time wears it out more rapidly.
Sources
This resource explains how flash memory works and who invented it. It also explains the future of flash memory. I must warn you that they accidentally confused the presence of electrons in the floating gate as the storing of information representing a ‘1’ rather than a ‘0’.
The website’s introduction is: “USB, which stands for Universal Serial Bus, is an industry-standard that was adopted in the 1990s. The USB flash drive, since it first went on the market in the early 2000s, has become ubiquitous due to its affordability. But how does it work and what do they mean for data recovery?”
This informational blog is packed with information. If you are looking for the uses of flash drives in the industry and the risks, visit this site first to determine if you need to keep researching.
This video tries to explain the full process of flash memory, starting with its creator. It not only covers how information is stored on a flash drive but also how it can be transferred to the computer.
“We've all been guilty of ripping our USB Drive out of our computers instead of ejecting them properly, only to receive the judgemental pop-up telling us we really shouldn't have done that. But when everything on the USB works fine next time you plug it in, you can't help but wonder: does it actually do anything when you safely eject your disk before removing it?” ~website
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