Solid State Removable Storage

Flash memory: An EPROM, or erasable programmable read-only memory, is a type of computer memory chip that retains its data when its power supply is switched off. From this technology we have the modern solid state storage devices known as flash memory or memory cards, including thumb drives and flash drives.

Removable solid state storage devices "Flash Memory" offer an incredible number of options at present and are popular for mall devices, such as digital cameras and PDAs. Flash memory is a type of solid-state technology, which basically means that there are no moving parts. Inside the chip is a grid of columns and rows, with a two-transistor cell at each intersecting point on the grid. The two transistors are separated by a thin oxide layer. One of the transistors is known as the floating gate, and the other one is the control gate. The floating gate's only link to the row, or wordline, is through the control gate. As long as this link is in place, the cell has a value of "1." To change the cell value to a "0" requires a curious process called Fowler-Nordheim tunneling. Tunneling is used to alter the placement of electrons in the floating gate. An electrical charge, usually between 10 and 13 volts, is applied to the floating gate. The charge comes from the column, or bitline, enters the floating gate and flows to a "ground". This charge causes the floating-gate transistor to act like an electron gun. The excited, negatively charged electrons are pushed through and trapped on the other side of the oxide layer, which acquires a negative charge. The electrons act as a barrier between the control gate and the floating gate. A device called a cell sensor monitors the level of the charge passing through the floating gate. If the flow through the gate is greater than fifty percent of the charge, it has a value of "1." If the charge passing through drops below the fifty-percent threshold, the value changes to "0."