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A flash memory device typically consists of one or more flash memory chips (each holding many flash memory cells), along with a separate flash memory controller chip. The NAND type is found mainly in memory cards , USB flash drives , solid-state drives (those produced since 2009), feature phones , smartphones , and similar products, for general ...
The memory cells are laid out in rectangular arrays on the surface of the chip. The 1-bit memory cells are grouped in small units called words which are accessed together as a single memory address. Memory is manufactured in word length that is usually a power of two, typically N=1, 2, 4 or 8 bits.
This ensures the device is operating properly, it maps out bad flash memory cells, and it allocates spare cells to be substituted for future failed cells. Some part of the spare cells is also used to hold the firmware which operates the controller and other special features for a particular storage device. A directory structure is created to ...
Over the following five years many device designers found ways to push the cap structure to increasingly tighter process geometries, successfully producing NAND at the 30 nm node with this approach. Charge trapping is still viewed as a future technology for NAND flash, but it is being considered more for vertical structures than for planar cells.
Logic circuits without memory cells are called combinational, meaning the output depends only on the present input. But memory is a key element of digital systems. In computers, it allows to store both programs and data and memory cells are also used for temporary storage of the output of combinational circuits to be used later by digital systems.
If needed, contents of the computer memory can be transferred to storage; a common way of doing this is through a memory management technique called virtual memory. Modern computer memory is implemented as semiconductor memory, [5] [6] where data is stored within memory cells built from MOS transistors and other components on an integrated ...
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A memory device is built from a grid of such "cells". The simplest method of reading is accomplished by measuring the electrical resistance of the cell. A particular cell is (typically) selected by powering an associated transistor that switches current from a supply line through the cell to ground.