Know Your NAND: Storage Types Explained

We throw a lot of terminologies around when we report on solid state drive storage and you probably noticed them all at some point. However, you might not know exactly what they are, what they mean, and what difference there is between it all. Today we’re taking a brief look at different NAND technology without going too much into the technical part of it.

The terms that we’ll talk about today will be SLC, MLC, and TLC along with both 2D planar and 3D NAND. One thing goes for all these terms, none is better than the rest in every aspect. All of them have their advantages and disadvantages. SLC, MLC, and TLC are the three types of NAND. In short, they stand for Single-Level Cell, Multi-Level Cell, and Triple-Level Cell NAND, and it refers to how many bits can be stored per cell.

SLC

Single-level cell NAND stores a single bit per cell and it offers the highest endurance of the three types. In return, it takes up more die space per capacity which decreases the possible capacities and increases the price. SLC is pretty much limited to the enterprise area where endurance is the most vital feature needed.

MLC

Multi-level cell NAND stores multiple bits per cell, but that name can be a bit misleading. While it technically could 2 or more bit per cell, it typically equates to 2 bits per cell. It provides a lower endurance than SLC but better than TLC. This is what you will find in most enthusiast drives where it delivers a great read and write performance

TLC

Triple-level cell NAND is the latest addition and it also stores multiple bits per cell, three to be exact. TLC has the lowest endurance of the three types, but it also offers the largest capacities for the smallest price. Manufacturers have also improved the endurance and reliability of TLC NAND a lot through refined manufacturing processes, error correction code, and wear levelling algorithms.

2D NAND vs 3D NAND

Planar NAND, also known as 2D NAND, is the traditional approach where 3D NAND is the newer one. 3D NAND was developed to address the challenges encountered in scaling 2D NAND to higher densities at a lower cost per bit. We all want faster solid state drives with more capacity for less money and that’s where 3D NAND comes into play. It is also the reason why we’re starting to see 2TB and even 4TB SSDs in 2.5-inch form factor for SOHO usage.

As NAND manufacturers worked to shrink the memory cells to do this in 2D NAND, they started to experience cell-to-cell interference caused which caused a reduction in the reliability. The obvious solution is to add another dimension and start to stack it – but that required rethinking and redesigns.

3D NAND offers a potential for higher capacity in a smaller physical space than 2D NAND. In comparison to planar NAND, 3D NAND can lower the cost per Gigabyte, improve electrical use to reduce power consumption, boost reliability, and provide higher data write performance. Where there are pros, there are cons too. 3D NAND has a higher manufacturing cost.

For the biggest part, 3D NAND is built with MLC NAND, but it works just as well with TLC. For the manufacturers, it is all about finding the balance between performance, capacity, and price in order to hit their target audience.

The first company to mass-produce 3D NAND was Samsung under the name Vertical NAND or V-NAND. The other companies have caught up since then and Micron, Intel, SK Hynix, Toshiba, and SanDisk all deal in it now.

Summary

In short, SLC, MLC and TLC define how many bits can be stored per cell and 2D and 3D define how those cells are put together; next to each other and stacked on top of each other too.

The various SSD form factors have no impact on which type of NAND is used. You can find them all in PCIe, M.2, and 2.5-inch form factor drives.