Specifications

Flash Memory Guide
5
4.0 Non-Volatile NOR and NAND Flash Technologies
Unlike Dynamic Random Access Memory (DRAM), Flash memory is non-volatile. Non-volatile memory retains data
even without being powered-on. For example, when a computer is turned o, all data that was in the computer’s
DRAM memory is lost; however, when a Flash storage device is removed from a digital camera, all data (and pictures)
remains saved on the Flash storage device. The ability to retain data is key for Flash memory applications such as
digital lm for digital cameras, mobile phones, tablets and other transportable devices.
There are two major technologies of Flash memory: NOR and NAND. Each technology has strengths that make it
ideal for dierent kinds of applications, as summarized in the following table:
NOR Flash NAND Flash
High-speed Access Yes Yes
Page-Mode Data Access No Yes
Random Byte Level Access Yes No
Typical Uses Networking Device Memory Industrial Storage
4.1 NOR Flash Memory
NOR, named after the specic data mapping (Not OR), is a high-speed Flash technology. NOR Flash memory provides
high-speed random-access capabilities, being able to read and write data in specic locations in the memory without
having to access the memory in sequential mode. Unlike NAND Flash, NOR Flash allows the retrieval of data as small
as a single byte. NOR Flash excels in applications where data is randomly retrieved or written. NOR is most often
found built into cellular phones (to store the phone’s operating system) and PDAs and is also used in computers to
store the BIOS program that runs to provide the start-up functionality.
4.2 NAND Flash Memory
NAND Flash was invented after NOR Flash, and is named after the specic mapping technology used for data (Not
AND). NAND Flash memory reads and writes in high-speed, sequential mode, handling data in small, block sizes
(“pages”). NAND Flash can retrieve or write data as single pages, but cannot retrieve individual bytes like NOR Flash.
NAND Flash memory is commonly found in solid-state hard drives, audio and video Flash media devices, television
set-top boxes, digital cameras, cell phones (for data storage) and other devices where data is generally written or
read sequentially.
For example, most digital cameras use NAND-Flash based digital lm, as pictures are usually taken and stored
sequentially. NAND-Flash is also more ecient when pictures are read back, as it transfers whole pages of data very
quickly. As a sequential storage medium, NAND Flash is ideal for data storage.
NAND Flash memory is less expensive than NOR Flash memory, and can accommodate more storage capacity in the
same die size.
Flash memory which stores a single bit per cell (e.g., a value of “0” or “1” per cell) is known as Single-Level Cell
(SLC) Flash.
5.0 Die-Stacking and Multi-Level Cell/Multi-Bit Cell Flash technologies
In order to economically increase the amount of bit-storage that a Flash memory chip can accommodate,
manufacturers utilize die-stacking and multi-level cell or multi-bit cell technologies. These technologies result in a
Flash memory chip having the capability to store more data in a single chip.