History

Flash memory (both NOR and NAND types) was invented by Dr. Fujio Masuoka while working for Toshiba circa 1980.^[1][2] According to Toshiba, the name "flash" was suggested by Dr. Masuoka's colleague, Mr. Shoji Ariizumi, because the erasure process of the memory contents reminded him of the flash of a camera. Dr. Masuoka presented the invention at the IEEE 1984 International Electron Devices Meeting(IEDM) held in San Francisco, California.

Intel Corporation saw the massive potential of the invention and introduced the first commercial NOR type flash chip in 1988.^[3] NOR-based flash has long erase and write times, but provides full address and data buses, allowing random access to any memory location. This makes it a suitable replacement for older Read-only memory (ROM) chips, which are used to store program code that rarely needs to be updated, such as a computer's BIOS or the firmware of set-top boxes. Its endurance is 10,000 to 1,000,000 erase cycles.^[4] NOR-based flash was the basis of early flash-based removable media; CompactFlash was originally based on it, though later cards moved to less expensive NAND flash.

Toshiba announced NAND flash at the 1987 International Electron Devices Meeting. It has faster erase and write times, and requires a smaller chip area per cell, thus allowing greater storage densities and lower costs per bit than NOR flash; it also has up to ten times the endurance of NOR flash. However, the I/O interface of NAND flash does not provide a random-access external address bus. Rather, data must be read on a block-wise basis, with typical block sizes of hundreds to thousands of bits. This made NAND flash unsuitable as a drop-in replacement for program ROM since most microprocessors and microcontrollers required byte-level random access. In this regard NAND flash is similar to other secondary storage devices such as hard disks and optical media, and is thus very suitable for use in mass-storage devices such asmemory cards. The first NAND-based removable media format was SmartMedia in 1995, and many others have followed, includingMultiMediaCard, Secure Digital, Memory Stick and xD-Picture Card. A new generation of memory card formats, including RS-MMC, miniSDand microSD, and Intelligent Stick, feature extremely small form factors. For example, the microSD card has an area of just over 1.5 cm², with a thickness of less than 1 mm; microSD capacities range from 64 MB to 16 GB, as of August 2009.^[5]