Flash Memory
If you have used a digital camera, then you know that even after switching off the camera, information about the photos you have taken is still available. Devices like mobiles, PDA, digital cameras, camcorders, digital audio recorders, smart pagers, GPS systems, etc. store information in a device called flash memory.
It works like a hard drive but is more compact and has fewer power requirements. Flash memory allows data to be written and erased from multiple locations. This ensures a much faster speed. Examples of flash memory devices are multimedia cards, secure digital cards, floppy disks, and flash cards.
Flash memory can be read or programmed one byte or word at a time in a random access pattern.
· Flash memory comprises cells or transistors made of a thin oxide layer.
· The cell has two transistors at its ends called the floating gate and the control gate. These operate on the 0 and 1 value concept.
· Applying an electric charge to the circuit runs Read/Write actions.
· Flash memory works using the tunneling principle to change the position of electrons in the floating gate.
· A charge of 10 to 13 volts is usually applied to the floating gate. Once charged, the electrons in the floating gate move to the other side of the oxide layer and change the charge to negative thus forming a barrier between the control and the floating gate.
· The threshold value of the charge regulates the functioning. When the flash memory is blank, then the value is one.
There are two basic forms of flash memory based on the logic gate: NOR flash and NAND flash. The NOR flash uses two gates and the NAND flash uses tunnel injection for writing and tunnel release for erasing.
Flash memory does not support random-access rewrite or erase operations. Blocks of memory must be erased all at the same time. Once a byte is programmed, it has to be erased before it can be changed. Compared to conventional hard disk drives, flash memory is much more expensive.
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