Flash Memory (sometimes called "Flash RAM") is a type of RAM that, like a ROM, retains its contents when the power supply is removed, but whose contents can be easily erased by applying a short pulse of higher voltage. This is called flash erasure, hence the name. Flash memory is currently both too expensive and too slow to serve as MAIN MEMORY, but is used as removable storage cards for digital cameras and pocket computers.
It is a variation of electrically erasable programmable read-only memory (EEPROM) which, unlike flash memory, is erased and rewritten at the byte level, which is slower than flash memory updating. Flash memory is often used to hold control code such as the basic input/output system (BIOS) in a personal computer. When BIOS needs to be changed (rewritten), the flash memory can be written to in block (rather than byte) sizes, making it easy to update. On the other hand, flash memory is not useful as random access memory (RAM) because RAM needs to be addressable at the byte (not the block) level.
Flash Memory gets its name because the microchip is so organized that a section of memory cells are erased in a single action or "flash." The erasure is caused by tunneling in which electrons pierce through a thin dielectric material to remove an electronic charge from a floating gate associated with each memory cell. Intel offers a form of flash memory that holds two bits (rather than one) in each memory cell, thus doubling the capacity of memory without a corresponding increase in price. Flash memory is used in digital cellular phones, digital cameras, LAN switches, PC Cards for notebook computers, digital set-up boxes, embedded controllers, and other devices.