How does a USB stick work? Easily explained

Data in the form of electrons are stored on a USB stick in so-called flash memory cells. In this article, we explain how a USB stick works in a simple and understandable way.

Building a USB stick

The structure of the memory is important in order to understand how data can be stored and called up on the USB stick:

• Each USB stick contains so-called flash memory cells that work like transistors. For the most part, they consist of a semiconductor material, for example silicon. There are two smaller areas made of much more conductive material, source and drain.
• Separated from the rest by an isolator, the floating gate is located between the source and drain. This component is the actual storage location of the flash cell. A positive or negative voltage can be applied via the control gate, which is connected to the floating gate.
• If a positive voltage is now applied to the control gate (about 3.3 volts), a channel is created between the source and drain, and current flows. This state is called the 0 state.
• Each of the cells can be either in the 0 or in the 1 state. A computer can then read out stored data from a large number of these cells.

Save data on the USB-Sick

The normal state of a flash memory cell is the 0 state, there is no information in the floating gate.

• To store information in a cell, the 1 state must be established.
• In order to reach the 1 state, a very high positive voltage must be applied (about 10 volts). Electrons jump from source and drain into the floating gate, it is charged negatively.
• Due to the isolation of the floating gate, the electrons cannot escape, the information is stored.

Read data on the USB stick

In order to read information, the computer must know whether the 1 or 0 state is present.

• A small positive voltage (3.3 volts) is applied and the current flow between source and drain is measured.
• In the 0 state, current flows through the channel between source and drain as described above.
• In the 1 state, the channel between source and drain remains closed because the negatively charged floating gate counteracts the voltage. There is no electricity.

Delete data from the USB stick

In order to delete information from the memory cell, the negative charge in the floating gate must be removed, the 0 state must be restored.

• To restore the 0 state again, a high negative voltage must be applied to the control gate. The charge in the floating gate is removed and the channel between source and drain opens again.

How do 1-states become readable data?

• There are billions of individual flash memory cells in a USB stick. Each memory cell represents a bit. One bit is the smallest storage unit, eight bits form a byte. A 4 GB USB stick has about 32 billion individual flash memory cells.
• Each memory cell has the 0 or 1 state, which creates a so-called binary code, which the computer reads out and outputs as text, audio file, image or other.
• For illustration, you can convert text online into a binary code.

Latest USB standard: USB 3.1 Type-C

Flash memory is also built into the fast SSD hard drives. Intel's new 3D Xpoint memories are even faster than the flash memories.