A Definition of Flash Memory
Flash memory is a persistent memory chip that is used for data storage and, due to its portability, for transferring data between devices, such as a computer and digital camera.
Flash memory has the ability to repeatedly store and delete data making it usable within USB flash drives, SD cards and Compactflash cards as well as inbuilt within digital cameras, mobile phones, solid state drives and MP3 players.
There are 2 main types of flash memory used within devices, being NAND and NOR. The type of memory within a device is depending upon the type of data that is required to be stored as well as the use of that data.
NAND Flash Memory
NAND type memory was first produced by Fujio Masuoka of Toshiba, who sought to create a memory chip that could retain the data stored to it even without a source of power. It was named Flash Memory due to its ability to quickly erase blocks of data.
NAND flash memory uses floating gate transistors connected in a NAND gate with several transistors connected in a series.
NAND memory suits bit-serial applications including hard drive emulation where access if made one bit at a time.
NAND memory is most often used within devices where large files are uploaded and replaced, including USB flash drives, digital cameras etc. It has a shelf life of approximately 100,000 write/erase cycles.
NAND chips allow denser layout and greater storage capacity per chip and they are able to contain faults within them and still be usable, in order to increase the amount of storage available, manufacturers reduce the size of the transistors that form them.
NOR Flash Memory
In 1988 Intel produced the NOR flash memory chip which became used on computer mainboards as the permanent read-only memory (ROM) that contains the BIOS allowing the computer to boot into the operating system.
NOR memory contains a ground for each cell with the other end connected to a bit line, making it appear like a NOR gate which gives it its name.
The NOR memory has a shelf life of 10,000 to 1,000,000 write/erase cycles and is most often used within mobile phones.
Flash memory is persistent and much cheaper that EEPROM and does not require power to retain the data stored to it. It also has a fast access time as well as a greater level of shock and temperature protection when compared to a standard hard drive.
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