flash memory

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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 memory

(1) See also Flash (multimedia authoring and playback system).

(2) The most popular non-volatile, rewritable memory chip. Extremely durable, flash memory is used in just about every electronic device, including USB drives, cameras, iPods, smartphones, tablets, computers and servers.

Erase in a Flash!
Evolving from the EEPROM chip, flash was invented by Toshiba in the mid-1980s and named after its ability to erase a block of a data "in a flash." Ironically, this block erasing is its least desired feature and one the industry would dearly love to eliminate (see future memory chips). For more about the flash cell architecture, see EEPROM.

NOR flash is like RAM, while NAND is like a hard drive. For example, in a digital camera, an internal NOR chip holds the software, while the removable memory cards are composed of NAND chips. Before any writing can take place, both NOR and NAND cells must be erased in large blocks, typically 128KB in size. See logic gate.

NOR for Software
First delivered by Intel in 1988, the NOR "linear flash" interface supports one-byte random access, which means a program's instructions stored in NOR flash are copied out and executed the same way computers have fetched instructions from main memory for decades. See memory.

NAND for Storage
One year after the first NOR chips, Toshiba developed the less costly NAND flash, which has denser cells and faster erasing and writing than NOR. A "flash translation layer" makes NAND flash look like a disk drive to the operating system (see FTL). All flash memory eventually wears out, but in practice, most users will have many years of service (see SSD write cycle). See MLC, charge trap flash, USB drive, memory card, solid state drive, flash BIOS and early memories.

From Spinning Platters to Flash
Slowly but surely, flash-based solid state drives (SSDs) are replacing the computer's hard disks for storage. Not only are SSDs faster, there is no read/write head to accidentally scratch a platter's surface (see head crash). See solid state drive.

USB Drives "Are" Flash Memory
The ubiquitous USB drives are not much more than a NAND flash memory chip.

Memory Cards Are the Camera's "Film"
Flash-based memory cards are used in all modern cameras and camcorders. This is an SD Card, which is the most popular (see memory card).

Disk Pack Storage - 1970s
The 16GB SD Card in the camera photo above holds eight times more storage than all the disk drives combined in this room full of ICL computers (SD Cards can hold 512GB and more these days). See disk pack. (Images courtesy of The National Museum of Computing, Milton Keynes, U.K., www.tnmoc.org)

Flash For Sale
This 2014 Micro Center ad highlighted the flash memory products people use every day. Class 10 SD Cards means a minimum of 10 MBytes/sec write speed for HD video recording. See SD Card classes. (Image courtesy of Micro Center, www.microcenter.com)
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