Compact Flash Memory and Data Recovery ( Part1)

Flash memory gets its name due to its microchip arrangement in such a way, that its section of memory cells gets erased in a single action or "Flash".

Both NOR and NAND Flash memory were invented by Dr. Fujio Masuoka from Toshiba in 1984.The name 'Flash' was suggested because the erasure process of the memory contents reminds a flash of a camera, and it's name was coined to express how much faster it could be erased "in a flash". Dr. Masuoka presented the invention at the International Electron Devices Meeting (IEDM) held in San Jose, California in1984 and Intel recognizes the potentiality of the invention and introduced the first commercial NOR type flash chip in 1988, with long erase and write times.

Flash memory is a form of non-volatile memory that can be electrically erased and rewrite, which means that it does not need power to maintain the data stored in the chip. In addition, flash memory offers fast read access times and better shock resistance than hard disks. These characteristics explain the popularity of flash memory for applications such as storage on battery-powered devices.

Flash memory is advance from of EEPROM (Electrically-Erasable Programmable Read-Only Memory)that allows multiple memory locations to be erased or written in one programming operation. Unlike an EPROM (Electrically Programmable Read-Only Memory) an EEPROM can be programmed and erased multiple times electrically.

Normal EEPROM only allows one location at a time to be erased or written, meaning that flash can operate at higher effective speeds when the systems using; it read and write to different locations at the same time.

Referring to the type of logic gate used in each storage cell, Flash memory is built in two varieties and named as, NOR flash and NAND flash.

Flash memory stores one bit of information in an array of transistors, called "cells", however recent flash memory devices referred as multi-level cell devices, can store more than 1 bit per cell depending on amount of electrons placed on the Floating Gate of a cell. NOR flash cell looks similar to semiconductor device like transistors, but it has two gates. First one is the control gate (CG) and the second one is a floating gate (FG) that is shield or insulated all around by an oxide layer. Because the FG is secluded by its shield oxide layer, electrons placed on it get trapped and data is stored within. On the other hand NAND Flash uses tunnel injection for writing and tunnel release for erasing.