How QLC and TLC are supercharging your SSDs

There are plenty of different terms you will encounter when looking to add a new drive to your PC or laptop. Whether that’s additional storage to what you’ve already have or to replace your machine’s main OS drive. We’re focusing on SSDs here as that’s the most recent technology, and beyond a few niches, spinning platter hard drives aren’t particularly relevant to modern PCs.

In this article we will run through the different NAND flash memory chip types you’ll find at the heart of SSDs, covering the technologies that have appeared over the years, but also focusing on those that are still relevant today.

It’s worth starting off by stating that SSD stands for Solid State Drive, and as the name suggests this storage technology is based non-volatile flash memory. This form of storage is much faster than hard disk drives (HDDs), providing access and throughput on a completely different level of HDDs. For instance, HDDs top out at between 100–200MB/s whereas the latest PCIe 5.0 SSDs can achieve over 10,000MB/s. SSDs are just faster than the HDD equivalents.

To understand how an SSD works, you need to dig down to their fundamental building blocks: the NAND flash cell that holds the information you wish to retain. SSD technology has quickly evolved from storing a single bit per cell (as used in SLC), to two bits per cell (MLC), then to three bits per cell (TLC), and then most recently to four bits per cell (QLC) all in a matter of a few years.

Why did the transition happen so quickly? Three reasons:

• SSD technology improved very quickly
• Industry flash production quickly shifted to the latest technology
• The cost benefits of newer technologies meant more gigabytes per dollar

Moving from SLC to MLC doubles the cell density. Moving to TLC gave an additional 50% density and then the latest jump to QLC provided an additional 33% Density. As an example: a normal M.2 SSD (using the M.2 2280 form factor) could be limited to just 128GB of capacity using SLC technology (a typical capacity when SSDs first launched) can now be replaced by a drive of the same physical size but offering up to 8TB of storage using QLC flash technology.

This huge increase in capacity isn’t outlandishly expensive either, because each improvement to the underlying technology equates to a reduction in NAND cost per GB. Endurance and latencies are impacted by storing more data in each cell, but overall, this is a net positive.

It does take more time to write multiple bits to a single cell, which means that SLC SSDs are the fastest option out there, but they’re significantly more expensive because of it. By multiple factors. They’re also not remotely needed for normal PC gaming or even workstation applications. About the only place you’ll see SLC SSDs today is in some servers.

The most-recent technology to hit the market has been the development of 3D NAND, which allows manufacturers to stack the cell layers on top of each other. This not only helps with SSD density, but performance and power-efficiency also benefit. 3D NAND has quickly become the standard and you’d be hard pushed to find a modern drive that is built using it.

As operating systems, games, and other applications grow, it shouldn’t come as a surprise to learn that CORSAIR uses 3D NAND to offer larger storage options in all its M.2 SSDs. Up to 8TB is available using the M.2 2280 form factor, while tiny SSDs, such as the M.2 2230 MP600 MINI are available in meaningful capacities.

Let’s dive into the details of the four different types of chips:

• Pro: Highest endurance, fastest performance
• Con: Very expensive and low capacities

Single-level cell (SLC) NAND stores only 1 bit of information per cell. It is typically used for servers and other industrial applications that require endurance over everything else. These drives cost around 30x more than QLC NAND and when looking at the popular M.2 format are limited to just 128GB.

• Pro: Cheaper than SLC
• Con: Slower and offers less endurance than SLC

Multi-level cell (MLC) NAND stores multiple bits per cell. In practice this equates to 2 bits per cell.

MLC is usually found in industrial products where endurance is not quite so important as would require SLC NAND and in customer drives where better endurance is needed than is available from TLC/QLC options.

CORSAIR launched its first MLC SSD back in 2009. The CORSAIR MP500 is still available to buy and still uses MLC NAND flash. More recent offerings have moved away from this technology though, as TLC and QLC drives are simply better for most users.

• Pro: Cheapest and high capacities
• Con: Low endurance

Triple-level cell (TLC) NAND can store 3 bits per cell, while Quad-Level Cell (QLC) NAND can store 4 bits per cell. Most consumer SSDs in the market today use TLC or QLC NAND Flash.

CORSAIR use TLC NAND on its fastest SSDs available today. Drives such as the PCIe 5.0 MP700 and the PCIe 4.0 MP600 PRO LPX both use TLC NAND. These drives are designed for high-performance systems and are built to house your main operating system and your most used applications.

There are a few QLC drives in our line up as well, and these are designed with high storage capacities in mind, or where value for money is paramount. The MP600 Core XT range offers the best cost-per-gigabyte of any of our offerings and is a great go to for anyone on a tight budget.