flash memory
(1) See also Flash.(2) A very popular non-volatile, rewritable memory chip used for storage. Extremely durable, flash memory is used in myriad portable devices, including digital cameras, digital music players, smartphones and tablet computers. USB drives "are" flash memory chips, and the solid state drives (SSDs), which are increasingly replacing hard disks in laptops, are also flash memory chips.
Years ago, flash replaced the permanent read-only-memory (ROM) chip on a PC motherboard that held the BIOS. Instead of having to open the case and physically replace the ROM BIOS chip, updated BIOS code could be downloaded into the flash chip (see BIOS). See firmware.
Evolving from the EEPROM, flash was invented by Toshiba and named after its ability to erase a block of a data "in a flash." Ironically, this block erasing is one of its least desired features and one the industry is trying to eliminate through the development of newer technologies (see charge trap flash and future memory chips). For more about the architecture of the flash cell, see EEPROM.
NOR and NAND
Flash chips are constructed of either NOR or NAND gates (see logic gate). NOR works like a computer's memory, while NAND is like a hard disk. For example, in a digital camera, an internal NOR chip holds the software, while NAND chips are in the removable memory cards. Before any writing can take place, both NOR and NAND flash cells must be erased in large blocks, typically 128KB in size.
NOR Flash for Software
Developed by Intel in 1988, the NOR "linear flash" interface supports one-byte random access, which means machine instructions can be fetched and executed directly from the flash chip (executed in place) just like computers fetch instructions from main memory. NOR flash has a lifespan of about 10,000 write cycles.
NAND Flash for Data Storage
Developed by Toshiba a year after Intel's NOR flash, NAND is more durable and less expensive. The cells are denser, and erasing and writing are faster. NAND-based flash memory is used for storage, and a "flash translation layer" (FTL) makes NAND flash look like a disk drive to the operating system (see FTL).
NAND cells can be rewritten about 100,000 times, and "wear leveling" distributes the writing across all the cells to improve longevity. In practice, most users will not wear out the flash memory in their devices. In 2008, Japanese scientists prototyped ferroelectric-based NAND flash (FNF) memory, which is said to be denser, use less power and be capable of tens of millions of writes. See USB drive, memory card and solid state drive.
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| USB Drives "Are" Flash Memory |
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| The ubiquitous USB drives are nothing more than a NAND flash memory chip. |
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| Memory Cards |
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| Memory cards are used in all digital still cameras and most camcorders. This is an SD Card, which is very popular (see memory card). |
flash memory [¦flash ′mem·rē]
(computer science)
A type of electrically erasable programmable read-only memory (EEPROM). While EPROM is reprogrammed bit-by-bit, flash memory is reprogrammed in blocks, making it faster. It is nonvolatile.
| flash memory - Flash Erasable Programmable Read-Only Memory |
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