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Difference Between NAND Flash and NOR Flash

NAND Flash vs NOR Flash

Flash memory is one of the most commonly used nonvolatile semiconductor memory types in the modern computing systems and in a wide range of mobile devices and consumer devices. NAND flash and NOR flash are the predominant forms of flash technology. Flash memory technology is an extension from EEPROM and NAND/ NOR stands for the gate architecture used in constructing the memory devices.

What is NAND Flash?

The flash chips are divided into erase segments called blocks, and data is stored into these erase blocks. In NAND flash architecture, these blocks are connected sequentially. The sizes of the erase blocks are 8kB to 32kB, which are smaller, allowing increased read, write, and erase speeds. Also, NAND devices are connected using a complicated serially connected interface and the interface can vary from manufacturer to manufacturer. In general, eight pins are used to convey, control, and retrieve data information. At a single instant, all the eight pins are employed, typically transferring data in 512kB bursts.

Structurally NAND architecture is designed for optimized high density lithography as a tradeoff of the random access capability to smaller block size. This makes NAND flash memory cheaper in terms of cost per volume. In theory, the density of the NAND flash is twice that of NOR flash.

NAND flash is suitable for data storage purposes. PC cards, compact flash, SD cards, and MP3 players use NAND flash drives as the memory.

What is NOR Flash?

NOR flash memory is the older of the two flash memory types. In the internal circuit configuration of NOR flash, the individual memory cells are connected in parallel; therefore, data can be accessed at random order. Because of this random access capability NOR has very short read times when retrieving information for execution. The NOR type flash is reliable and causes less bit flipping issues.

The density of erase blocks in NOR flash is lower than the NAND architecture. Therefore, the cost per volume is higher. It also consumes higher level of energy at standby though, during operation, it consumes relatively lower level of energy compared to NAND flash. Also, the write speed and erase speed are low. But the code execution with NOR flash is much higher because of the build in random access architecture.

The NOR flash is used for code storage in devices, such as the code storage unit of digital cameras and other embedded applications.

What is the difference between NAND Flash and NOR Flash?

• NOR flash is older than the NAND flash architecture.

• NAND flash has a much higher density of erase blocks than the NOR flash.

• In NAND flash architecture, the erase blocks are connected sequentially while, in NOR flash, those are connected in parallel.

• Access type of NAND is sequential while NOR has random access.

• Therefore, the read speed of NOR is faster than the NAND.

• The NOR flash has very slow erase speed compared to NAND flash, and the write speed of the NOR is also slow.

• NAND can go through 100,000-1,000,000 erase cycles while NOR can sustain only about 10,000-100,000 cycles.

• NOR flash is more reliable and has less percentage of bit flipping, while NAND flashes require an addition bit for error management.

• NAND flashes are suitable for data storage while NOR flashes are suitable for code storage.

• NAND flash memory is cheaper compared to NOR flash memories in terms of cost per volume.

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