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Summary

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.


Anyone who has tried the great performance of SSD will tell you how impressive the SSD will be. With faster system and software loading speed and high efficiency, SSD are with greater durability and performance when comparing with traditional HDD. There is no doubt that  SSD will become the main part in any new devices.

Some users may confuse about that why SSD with same capacity but are expensive than others? Similar to race cars, it is all about what is under the hood.

Latest news in 2019: In the past SLC, MLC and TLC especially TLC have been widely used in SSD. But with the rapid development of technology and users’ demand, a new type of flash memory QLC has been released. QLC (Quad-level Cell) takes the advantages of larger capacity and lower price. If you want to know more about QLC, please follow us on “Details of QLC (Quad-level Cell)”.

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 newer and better storage media when comparing with traditional HDD. It is adapted with the non-volatile memory which can still save data even power off.
NAND flash memory is built up of many cells that holds bits and those bits are either turned on or off through an electric charge. The organization of the cells represents how the data stored on the SSD. The number of bits in those cells also determine the naming of the flash, for example Single Level Cell (SLC) flash contains a single bit in each cell.
Because the circuit board of the SSD has to fulfill the industrial standard, MLC doubles the  amount of bits per cell whereas TLC triples. And this opens up a trendy of high capacity SSD. And now, the manufactures are trying to minimize the production cost of storage of each bits of NAND flash and improve the capacity at the same time. As a result, QLC – Quad Level Cell which provide 4 bits in each cell is released recently.
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.

Single Level Cell - SLC

Single Level Cell - SLC

Single level cell, also called SLC, has the advantage of being the most accurate when reading or writing data. Besides, it has the longest life span over any other type of flash memory.
The read/write life cycle of SLC is expected to be between 90,000 and 100,000. This type of flash memory has done exceptionally well in the enterprise because of it’s life span, accuracy and overall performance. It is not so common in home computers with this type of NAND due to its high cost and low storage capacities.

Pros:

  • 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.

Cons:

  • 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

Multiple Level Cell, short for MLC, stores 2 bits of data on one cell. The advantage is to lower the cost of manufacturing. As we all know, the cost in flash memory production is generally passed onto conumer in the end.
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.

Pros:

  • Lower production cost and provides larger SSD capacities.
  • More stable than TLC flash.
Cons:
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 flash stores 3 bits of data per cell and it is the cheapest form of flash to manufacture. The biggest disadvantage of TLC is that it is only suitable for consumer usage and not be able to meet the standards for industrial use. Read/write life cycles are considerably shorter at 3,000 to 5,000 cycles per cell.

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

Cons:
  • 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

Comparing with TLC, the storage density of QLC increase 33% with each cell can save 4 bit data. Besides, the write cycle of QLC could reach 1000 times, which is equal even better than TLC. And the price of QLC is lower than that of TLC at the same time.
Advantages:
  • 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.

Conclusion

Conclusion

So far, you probably have some ideas on the difference among QLC, SLC, MLC and TLC NAND flash. And we can get a direct comparison from the following chart.

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★★★★★★★★☆☆★★☆☆☆★★☆☆☆
Endurance★★★★★★★★☆☆★★☆☆☆★★☆☆☆
Cost★★★★★★★★☆☆★★☆☆☆★☆☆☆☆
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.

Part 8: Price of Hard Disk with 4 Different NAND Flash Memory

Part 8: 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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