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This guidance will introduce the NAND flash of SSD. We will list the differences among QLC, SLC, MLC and TLC as well as pros and cons of each NAND flash to help you choose a suitable SSD.

Solid State Drives (SSDs) are increasingly favored for their speed, durability, and reliability, with NAND Flash SSDs being particularly prevalent due to their non-volatile memory, which retains data without power. Originating in the early 2000s, NAND Flash technology first appeared in USB drives and memory cards before the advent of SSDs in 2007. Offering faster read and write speeds than traditional hard drives, NAND Flash SSDs excel in high-performance computing and are inherently more durable due to the absence of moving parts. With ongoing technological advancements, their use has expanded from consumer gadgets to enterprise storage systems. Notable NAND Flash SSDs are available from Samsung, Intel, and Western Digital, varying in size and capacity, and are characterized by low power usage, rapid data transfer rates, and robust reliability.
SLC (Single Level Cell), MLC (Multi Level Cell), TLC (Triple Level Cell), and QLC (Quadruple Level Cell) are types of flash memory, each with varying performance and reliability.

SLC offers the highest performance and reliability, storing one bit per cell, making it ideal for high-demand applications like servers and military technology.

MLC, storing more than one bit per cell, provides good performance and is common in consumer devices like cameras and smartphones.

TLC, with three bits per cell, has lower performance but increased storage capacity, used in external drives and budget smartphones.

QLC, storing four bits per cell, has the highest capacity but lowest performance, suitable for long-term storage and archiving.

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The Anatomy of an SSD

The Anatomy of an SSD

Before analyzing SSD, we need to figure out the anatomy of an SSD:
A. NAND Flash: This part is the location save your data, in blocks of non-volatile (does not require power to maintain data).

B. DDR Memory: Small amount of volatile memory (requires power to maintain data) used to save cache information for future access. Not available on all SSD.

C. Controller: The main connector between the NAND flash and your computer.

ssd component2

What is NAND Flash Memory?

What is NAND Flash Memory?

NAND flash memory is a type of non-volatile storage technology that is commonly used in modern electronic devices. It was first proposed in 1987 by Toshiba and involves storing data in a series of memory cells that are organized into blocks or groups. These blocks can be quickly erased and rewritten, allowing for flexible and efficient storage.

NAND flash memory is made up of a series of transistors, each of which can store a single bit of information. These transistors are organized into pages, and multiple pages are combined to create a block of storage. When data is written to NAND flash memory, it is stored in these blocks and can be quickly accessed when needed.

One of the key advantages of NAND flash memory is its non-volatile nature, which means that it can retain data even when the power is turned off. This makes it well-suited for use in portable devices like smartphones and tablets, as well as in enterprise-class solid-state drives (SSDs).

However, NAND flash memory also has some limitations and challenges that can impact performance and reliability. One of the biggest challenges is wear, as NAND flash memory has a finite number of program/erase (P/E) cycles before the storage cell integrity begins to fail. Most basic flash products are rated for 100,000 P/E cycles before this happens, though some types of NAND flash chips are rated for 1 million P/E cycles or more.

Another challenge is erasure, as NAND flash memory requires entire blocks to be erased at once. This can lead to slow write speeds and reduced overall performance. Additionally, cross talk and sensitivity can also impact the reliability of NAND flash memory.

Despite these challenges, NAND flash memory remains a critical component in many modern electronic devices. Advances in memory cell technology have allowed for increased density, performance, and reliability, and the development of techniques like multi-level cell (MLC), triple-level cell (TLC), and quad-level cell (QLC) have allowed for even greater flash storage capacity. As technology continues to evolve, NAND flash memory is likely to remain an important storage technology for years to come.

different ssd
However, different NAND flash basics have their own characteristics. Here we are going to introduce more about the different flash memory (QLC, SLC, MLC and TLC). Understanding your own need and choose the suitable SSD.
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Single Level Cell - SLC

Single Level Cell - SLC

Single-level cell (SLC) is a type of flash memory that has been widely used in commercial and industrial applications where high performance and long-term reliability are essential. SLC is the simplest form of flash storage as it stores only one cell per bit, which makes it the longest-lasting flash storage available in the market. The firmware in SLC flash does not need to go through several levels of data in the cells during read and write operations, which reduces the likelihood of errors and makes it a suitable option for performance-critical applications.

SLC flash is designed for applications that require high performance and low latency. It is commonly used in embedded systems, high-performance servers, and other applications that demand high-speed data transfer. SLC flash storage devices are rated at 100,000 write cycles per cell, which is significantly higher than the 10,000 write cycles per cell for multi-level flash storage devices.


  • The fastest NAND flash memory in reading/writing.
  • Has the longest lifespan and charge cycles over any other type of flash.
  • Being most accurate when reading/writing.


  • The most expensive type of NAND flash.
  • Often provided in smaller capacities.

Recommended for:
Industrial use and workloads that require heavy reading/writing cycles such as servers.

Multi Level Cell - MLC

Multi Level Cell - MLC

Multi-Level Cell (MLC) technology is widely used in the flash memory industry due to its high data density and cost-effectiveness. MLC flash memory stores multiple bits of information in a single cell, typically 2 bits per cell, using 4 charge values or levels. This is achieved by modulating the voltage supplied to the cell, which can vary the amount of charge stored in it.

The benefits of MLC flash memory are primarily cost-related, as it offers a lower cost per unit of storage due to the higher data density. However, MLC flash memory also has certain drawbacks that must be taken into account. These include lower write speeds, lower endurance (i.e. a lower number of program/erase cycles), higher power consumption, and a higher bit error rate compared to other flash memory types like SLC.

For consumer SSD, using MLC flash memory will be preferred for its lower costs. Although the read/write life is about 10 thousand time per cell, it is enough for normal use.


  • Lower production cost and provides larger SSD capacities.
  • More stable than TLC flash.
Not so durable and reliable as SLC or enterprise SSDS.

Recommended for:
Everyday consumer use, gamers, etc.

Triple Level Cell - TLC

Triple Level Cell – TLC

TLC, or Triple Level Cell, is a type of NAND flash memory that is capable of storing three bits of information per cell. Initially introduced by Toshiba in 2009, this technology was adopted and mass-produced by Samsung Electronics in 2010. TLC NAND flash is known for its high storage density and low cost per bit, making it an attractive option for manufacturers.

One of the key advantages of TLC NAND flash is its high storage density. By storing three bits of information per cell, TLC flash can triple the capacity of SLC (Single Level Cell) and offer 1.5 times more storage than MLC (Multi Level Cell). This means that NAND manufacturers can achieve the same capacity with a TLC die as they do with a 32 Gb MLC die by reducing the die size from 16 billion cells to 10.667 billion cells, resulting in significant cost savings.

However, TLC NAND flash also has several drawbacks when compared to SLC and MLC flash. One of the main drawbacks is its slower performance, which is due to its eight voltage levels. In contrast, SLC has only two levels of charge and MLC has four levels. This means that TLC flash programs data more slowly because it requires more time to store the additional voltage levels.

TLC NAND flash also has a higher bit error rate than SLC and MLC flash, which makes the read process more sensitive to noise. This is because the small difference between its eight voltage levels can lead to values shifting as the flash cell wears out, resulting in errors.

Lower production cost leads to a cheaper SSD choice in SSD market.


  • The life span of TLC is much shorter than that of SLC and MLC.
  • The read/write speed is the slowest among all flash types.

Recommended for:
Everyday consumer use, web/email machines, netbooks, and tablets.

Quad Level Cell – QLC

Quad Level Cell – QLC

QLC (Quad Level Cell) is the latest evolution in NAND flash memory technology. As the name suggests, QLC flash is capable of storing four bits of data per cell, which translates to 16 possible voltage states. With this increase in density, QLC flash offers much higher storage capacity than its predecessors. QLC flash is primarily designed for read-centric loads, where large amounts of data are read frequently but not necessarily written often.

While QLC flash offers significant advantages in terms of capacity and cost, it does come with trade offs. The biggest drawback of QLC flash is its low writing durability, which is the number of times a storage cell can be written to before it starts to fail. QLC flash has a limited number of program/erase (P/E) cycles, at around 1,000, compared to SLC flash’s 100,000 P/E cycles.

QLC flash is best suited for applications where data is frequently read but not written as frequently, such as content storage or backup repositories. QLC flash can also be used in applications where data is written in large chunks at a time, like video streaming services or cloud storage.

To address the durability issue, manufacturers have developed techniques to mitigate the impact of repeated writes on QLC flash. One approach is to use SLC or MLC flash as a cache for QLC drives. This technique can significantly enhance QLC flash’s effective lifespan.


  • Writing and accessing can be processed by fewer driver software than the other 3 types of NAND flash memory.
  • More storage capacity, higher storage density and lower price.
Disadvantages: The performance and life span of QLC is so good as SLC or MLC, but is nearly equal to TLC.
Recommended for: Want to make SSD with QLC flash memory to be the data storage disk. If you have a heavy demand for data storage and do not save much data in computer, or you do not have enough budget on SSD, it is recommended to try SSD with QLC flash memory.
If you are worrying about the life span or transmission speed of QLC, information provided below could help you.

1. The Life Span of QLC has been Expended

A few years ago, people predicted that the write cycles of QLC just have 100-150 times. And many users worried about its life span as well. However, Crucial and Toshiba said that test of the life span of 3D QLC flash memory proved that it have 1000 write cycles which is 10 times of the prediction. Actually, the expend of life span mainly dues to 3D NAND.
Generally, SSD which is applied with advanced technology will get a larger storage capacity but with a shorter lifespan. In order to get a larger capacity and keep the life span. Crucial and Toshiba launch the joint development of 3D NAND technology. Different from traditional NAND memory, 3D NAND stacks memory cells vertically which could reach 32 layers maximum. As a result, single MLC memory chip could provide a storage capacity of 32GB while single TLC memory chip could add 48GB.
2D 3D NAND comparison
However, the life span of QLC SSD is still shorter than that of SLC and MLC. It is recommended user do not make QLC SSD to be the system disk.

2. The Transmission Speed of QLC SSD is not so Poor

Parts of main manufacturers of hard disk have released the transmission speed of own-produced QLC SSD. From the released report, the performance of QLC SSD is not so bad.
SSD Brand & ModelContinuous Reading SpeedContinuous Writing Speed
Intel 660p 542GB QLC SSD1500 MB/s1000 MB/s
Crucial P1 500GB QLC SSD1900 MB/s950 MB/s
It is so common that the performance of SSD degrade. More and more SSD will adapt the QLC flash memory after its release. But similar situation could not be avoided as well. Even if the performance of QLC SSD would degrade, its performance is still better than that of traditional HDD. In conclusion, QLC SSD is not so bad as we believed. When we want to purchase the QLC SSD, please pay more attention to factors like manufacturers, quality, warranty and price.



In conclusion, the selection of the type of NAND flash memory that is most suitable for a particular application depends on various factors such as cost, performance, endurance, and density. For low-cost and low-density applications, QLC NAND flash memory is a popular choice, while MLC NAND flash memory is commonly used in high-performance applications. SLC NAND flash memory is ideal for applications that require high levels of endurance, and TLC NAND flash memory provides a balance between cost and performance. Understanding the differences between these types of NAND flash memory is essential when choosing the right memory for a particular application.

NAND Flash

SLC - Single Level Cell

MLC - Multi-Level Cell

TLC - Triple Level Cell

QLC – Quad Level Cell

Read/Write Cycles90,000-100,0008,000-10,000500-10001000
Bit Per Cell1234
Writing Speed★★★★★★★★☆☆★★☆☆☆★★☆☆☆
UsageIndustrial/EnterpriseConsumer/GamerConsumerUsers has a huge demand on data storage
Besides, people believe that SSD has a low power consumption. Whether the power consumption will be different among SSD with different NAND flash memory? Here, comparison will be make below.
SSD Brand & ModelNAND Flash Memory TypeReading Power ConsumptionReading Power Consumption/hourWriting Power ConsumptionWriting Power Consumption/hour
Western Digital S240G1G0A 240GBSLC2.000 W0.002000 kW·h2.5 W0.002500 kW·h
Samsung 970 PRO 512GBMLC5.200 W0.005200 kW·h5.2 W0.005200 kW·h
Kingston A1000 480GBTLC0.458 W0.000458 kW·h0.908 W0.000908 kW·h
Intel SSD 660p 542GBQLC0.100 W0.000100 kW·h0.1 W0.000100 kW·h
In fact,factors like brands, model, types of NAND Flash, reading and writing power consumption will influence the power consumption of SSD. From the chart above, we can find that the reading and writing power consumption of TLC and QLC SSD is lower than that of SLC and MLC SSD. But, the power consumption of SSD is low, which could be ignored.

Price of Hard Disk with 4 Different NAND Flash Memory

Price of Hard Disk with 4 Different NAND Flash Memory

Here, we will introduce the price of SSD with 4 different NAND flash memory. Hope it can help you find the desired SSD with the introduction above. The price of SSD will be influenced by factors like brand, model, capacity and type of NAND flash memory.
SSD Manufacturer and ModelNAND Flash MemoryPrice on Amazon ($)Dollars/GB
Western Digital S240G1G0A 240GBSLC$42$0.18
Silicon SP240GBSS3S56B25AZ 240GBSLC$89.99$0.37
Samsung 970 PRO 512GBMLC$167.99$0.33
Kingston KC1000 480GBMLC$204.99$0.43
Intel DC S3520 480GBMLC$320$0.67
Kingston KC400 512GBTLC$99.99$0.2
Intel 600P M.2 2280 512GBTLC$100$0.2
Lexar NS100 480GBTLC$85.99$0.18
Intel SSD 660p 542GBQLC$89.99$0.17
Crucial P1 500GBQLC$89.99$0.18
ADATA SU630 480GBQLC$57.99$0.12

Source: Amazon, Jan, 2019/1/7

In conclusion, most SSD now adapts MLC and TLC NAND flash memory. Although SLC can provide a stable performance, it is not so popular in common SSD. And the new-born QLC NAND flash memory will be widely used in SSD in the future as it has a reasonable price. And the QLC SSD we have mentioned in the chart are new products released by Intel, Crucial and ADATA recently. It is recommended to keep focus on QLC SSD.

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