NAND is a cost-effective type of memory that remains viable even without a power source. It’s non-volatile, and you’ll find NAND in mass storage devices like USB flash drives and MP3 players. NAND memory is a form of electronically erasable programmable read-only memory (EEPROM), and it takes its name from the NAND logic gate.
NAND Flash Memory
NAND memory uses floating-gate transistors to store information without a power supply. All electrical circuits depend on some sort of power to create a difference in charges across the cell, and this power forces electrons to move through the gate.
With this return to the off state, volatile types of memory like random access memory (RAM) lose their data. The floating gate system solves this problem by using the second gate to collect and trap some electrons as they move across the cell. Electrons stuck to the floating gate remain in place without voltage and continue to store a value regardless of whether the chip has a power connection.
NAND Block Memory: Improving Speed
Each block of NAND memory contains a set number of pages. Within those pages are bytes for storing data and bytes that add more memory to each page and store error-correcting code.
A 512 KB block, for example, would be arranged in 128 pages, each containing 4,096 bytes, plus 128 additional error-correcting bytes per page.
Along with its physical construction, block organization helps gives flash memory its speed, but the feature does not apply to every function. You can write and access NAND memory in page units, but you can only erase entire blocks at a time.
Nand vs Nor
The two types of flash memory, NOR and NAND, differ in the way they read and arrange their data.
-Accessing NOR flash memory works similarly to accessing random-access memory (RAM). You can execute in place (XIP) programs stored in NOR without having to copy the programs to RAM first.
-In contrast, NAND does not have XIP capabilities, and thus requires the use of RAM to execute any program it stores. You can read data stored on NOR flash slightly faster than data on NAND because there’s no option to use random access. You can only read NAND data one page at a time.
However, NAND memory is much faster in every other way. You can only edit either type of flash memory once you erase an entire block, but NOR flash erasure requires a much more complicated procedure. This process slows down all functions significantly; in fact, you can erase NAND at 1,250 times the speed of NOR.
Unfortunately, this speed and NAND memory architecture’s unique features make NAND slightly less reliable than NOR.
Advantages and Disadvantages of NAND
-Cost: NAND is cost-effective per byte and has a high storage capacity for its physical size.
-Endurance: NAND cells eventually wear out as their transistors degrade. A NAND chip lasts until it reaches its write-cycle limit, after which it will no longer be able to store new data. A NAND chip can withstand anywhere from 1,000 to 100,000 erasures, depending on the brand, model, and design. NAND chips are physically sturdy and more durable than magnetic forms of storage.
-Replaceability: When NAND flash memory wears out, you can replace the chip with a compatible component.
-NAND shortage: A combination of high demand and a trend toward manufacturing denser 3D NAND technology (also known as vertical NAND) resulted in a NAND shortage that began in 2016. Two-dimensional, or planar, NAND is still the more cost-effective type as of 2018.
NAND memory is especially useful in devices that need to be able to store and frequently erase and replace large files, such as tablets, USB drives, and digital cameras.