SSDs have revolutionized the desktop and laptop industry — retiring old mechanical disks thanks to its lightning speed, ease of installation, and resistance to shock and strain.
The SSDs are now very popular. Without having to focus on mechanical disks (now usable exclusively as data disks for network-attached storage (NAS) or as backup disks, it is now possible to buy new SSDs of 1TB and more at competitive prices.
During the purchase of an SSD, you will surely have come across some strange acronyms, which apparently mean nothing but which in reality can indicate the quality of the chosen drive, regardless of the model or capacity.
In this guide, we will show you what do SLC, MLC, TLC, QLC, and PLC really mean, ie the abbreviations next to the SSD name or in its description.
How to choose the best SSD?
In order to choose the best SSD, we will have to pay attention to the abbreviations SLC, MLC, TLC, QLC, and PLC, which are often not indicated in the titles of the products sold online or on the technical datasheets of the SSDs sold in a computer store.
To obtain this information, we will have to access the detailed technical data sheet of the drive available at the manufacturer’s website.
So let’s understand in detail what these acronyms mean, and why they are so important in choosing a new SSD.
Terabytes Written (TBWs)
Normally speaking, SSD durability is expressed as TBW. This is the number of terabytes that can be written to the drive before it fails, which means that the TBW is kinda like the lifespan of SSD.
An example from Samsung SSDs, they state that their Samsung SSD 850 PRO SATA, with a capacity of 128 GB, 256 GB, 512 or 1 TB, can handle 150 terabytes written (TBW), which is equal to a 40GB daily read/write workload over a period of ten-years.
Samsung even promises that this product will be able to “withstand up to 600 terabytes written (TBW).” A normal office user writes approximately between 10 and 35GB on a normal day.
TBWs are also “safe level” estimates — well, SSDs commonly exceed these limits.
NAND memory indications
The strange acronyms we talked about in the introduction represent different types of NAND cells, that is, the cells that function as a “data warehouse” within SSDs.
Compared to mechanical disks — which used a magnetic disk and a head, in SSD, NAND flash storage is the building blocks of the memory cell. These are the base units onto which the data is written in an SSD.
Each memory cell will be able to accept a certain amount of bits, which will be registered on the storage device as 1 or 0. These cells are arranged in a particular way or functioning with precise characteristics.
The strange acronyms — SLC, MLC, TLC, QLC, and PLC — that are explained below provide you with a valuable indication of the type of NAND cells that we can find inside the drive, each with different performance characteristics.
SSDs: SLC vs MLC vs TLC vs QLC vs PLC
SLC: Single-Level Cell
The simplest cell type is SLC. SLCs accept one bit per memory cell, offering considerable advantages in terms of speed and reliability since they are less error-prone, so they are considered very reliable and durable.
SLC SSDs are very fast and last much longer than other types of cells. For this reason, they have a very high price and are usually offered only for SSDs in the business environment where data loss is less tolerable, and durability is needed. And not for the consumer environment — ie disks reserved for domestic use — they are used only to provide a fast cache to the entire disk.
MLC: Multi-Level Cell
MLC SSDs allow you to write two bits to a cell — yeah, the name multi doesn’t really suit it. MLC SSDs retain much of the single-cell benefits but increasing the total capacity of the cell.
They tend to be slower than SLCs, also these take hit on durability and reliability because data is written to the NAND flash more often than with an SLC, but they make up for this small flaw with greater capacity and better value for money.
TLC: Triple-Level Cell
The cheapest SSDs are indicated with the abbreviation TLC. They allow you to save three bits in a single cell but sacrifice something pretty important factors — which is speed and duration. Although they don’t break immediately but last less than the models seen previously.
The TLC cell is currently the most popular in the consumer environment, since they still offer a good compromise between duration, capacity and speed, even if they are not recommended for use as data discs. Don’t get me wrong, TLCs last several years.
QLC and PLC: Quad-Level Cell and Penta-Level Cell
Similarly, QLC drives can write four bits per cell, and PLC SSDs can write 5 bits per cell.
You can see modern SSDs like QLC and PLC are moving towards an even greater compression of the amount of bits that can be recorded in a single cell. However, such a high number of bits saved in a single cell has a downside — they do not last long, at least when compared with the types of cells seen previously.
Even if the minimum duration values go far beyond the real capacities with which SSDs are used, this disadvantage is kind of major and taken into consideration — there is a possibility of having to change the SSD within 5 years of purchase.
From a performance point of view, QLC and PLC SSDs are very good, even if they do not reach the speeds seen with single cells (SLC), but still, they are good.
When choosing a new SSD disk, it is advisable to inquire about the type of cell immediately it has to know precisely its estimated duration, the performance it can achieve, and the maximum capacity for that particular type of cell.
If we do not know which SSD to choose between two apparently identical models, we advise you to focus on MLC or TLC SSDs, leaving the SLC only to gaming PCs or PCs on which the SSD must operate as a data disk. And don’t forget to look at there TBWs too.