What are QLC flash and TLC flash? What is the difference between QLC flash memory and TLC flash memory?

Flash memory is one of the most commonly used devices, and flash memory exists in storage devices such as SSDs. But, do you really know enough about flash memory? In order to enhance your understanding and understanding of flash memory, this article will introduce QLC flash memory and TLC flash memory related content.

Flash memory is one of the most commonly used devices, and flash memory exists in storage devices such as SSDs. But, do you really know enough about flash memory? In order to enhance your understanding and understanding of flash memory, this article will introduce QLC flash memory and TLC flash memory related content.

What are QLC flash and TLC flash?  What is the difference between QLC flash memory and TLC flash memory?

I. Introduction

We are eager for a large-capacity SSD, but the price of a few thousand yuan for a large-capacity SSD that exceeds TB is practically meaningless for users with limited payment capabilities. The cost of SSD mainly comes from flash memory, and TB capacity can be achieved in TLC flash memory, but the price has not been lowered. Only by continuously developing new types of flash memory and solving the contradiction between capacity and price can SSD truly play its due role in the era of big data.

At this time, QLC flash memory came into being. At present, Toshiba and Western Digital have announced the successful development of 3D NAND flash memory chips based on four-bit cells, namely QLC flash memory, which also means that QLC SSD is coming. So, what is the difference between it and TLC flash memory, can it replace TLC as the mainstream flash memory of SSD choice?

2. QLC flash memory particles

Before talking about QLC, I think it will help everyone to understand it by talking about TLC first.

Friends who have bought SSDs should have heard of TLC flash memory particles. In 2017, the overall TLC SSD shipments accounted for nearly 75%, and the SSD market accounted for a larger proportion. That is to say, the solid state drives that everyone buys are basically It’s all from TLC.

QLC is a product that is expected to succeed him in the future!

There are several types of flash memory particles: SLC, MLC, TLC, QLC.

What are QLC flash and TLC flash?  What is the difference between QLC flash memory and TLC flash memory?

It will be clearer for everyone to refer to the above picture to explain

SLC single-bit cell (each Cell only stores 1 data, there are 21=2 states, that is, 0 and 1, that is, there are only two different voltage states), because it is stable, it has the best performance and the longest life. Long (theoretical rewritable 10W times), the cost is also the highest, the earliest top particle, but because of cost issues, it has disappeared from everyone’s field of vision.

MLC dual-bit cell (each Cell cell stores 2 data, 22=4 states, 00/01/10/11, so there are four different voltage states), that is, there are only two different voltage states) performance , Life (theoretical rewritable 1W times), cost is considered balanced among several types of particles, replacing SLC products, the absolute mainstream particles before TLC, and currently mainly used for high-end and enterprise-level products.

TLC three-bit cell (each Cell cell stores 3 data, 23=8 states, not detailed, as shown in the figure above, there are eight different voltage states), low cost, large capacity, but shorter and shorter lifespan (theoretically Erase and write 1500 times), but with the maturity of the technology, the current life problem has been solved, and it has become the most mainstream product in the current flash memory particles.

QLC four-bit cell (Each Cell cell stores 4 data, 24=16 states, not detailed, as shown above, there are 16 different voltage states), lower cost, larger capacity, but shorter lifespan (theory It can be erased and written 150 times), and there are still problems that need to be solved urgently if it wants to be a successor to TLC.

Note: The more data stored per Cell, the higher the capacity per unit area, but at the same time, the more different voltage states, the more difficult it is to control, which leads to poorer particle stability and lower lifespan. There are pros and cons.

What are QLC flash and TLC flash?  What is the difference between QLC flash memory and TLC flash memory?

I have to admit that the emergence of TLC flash memory has greatly increased the capacity of SSDs and reduced the price of SSDs to a certain extent. However, the problem of SSD prices has not been solved yet, and large-capacity SSDs are still expensive. The storage solution of small-capacity SSD + large-capacity HDD is not as good as a simple large-capacity SSD after all.

When QLC flash memory was born, perhaps cheap and super-capacity SSDs changed from ideal to reality.

Three, the difference between QLC and TLC

What are QLC flash and TLC flash?  What is the difference between QLC flash memory and TLC flash memory?

1. Life

Some time ago, Toshiba said that its QLC NAND has as many as 1,000 P/E programming erase and write cycles, breaking the curse of 100-150 times, which is comparable to the lifespan of TLC flash memory particles. If it really meets this standard, then QLC SSD will be able to enter the market with confidence.

The life span of 1,000 cycles is not so terrible for ordinary people. The average daily write volume rarely exceeds 10GB, so we assume that it is 10GB, 120GB QLC SSD, and the write life reaches 120 TB. Assuming that the write amplification factor is assumed to be 3 or even 5, it will be difficult to write it badly within three years. And the high capacity of QLC flash memory also means that it can be over-provisioned in the QLC drive to extend the effective life of the product itself.

At present, the warranty period of TLC SSD generally reaches 3 years, and some even reach 5 years. So what is there to worry about QLC lifespan issues?

2. Stability

QLC flash memory stores 4 bits of charge and has 16 states, while TLC stores 3 bits of charge and has 8 states. This means that the storage density of QLC flash memory units is greater, twice that of TLC, and a single chip can reach 256GB or even 512GB. However, because of this, the voltage of QLC flash memory is more difficult to control and interference is more complicated, and these problems will affect the performance, reliability and stability of QLC flash memory. But this living case of TLC is in the front, it will be easier to solve.

3. Cost

Although QLC only adds a bit in the Electronic unit of TLC, its required technical content is very high. This is because it is not only necessary to add a bit unit on the original basis, but also requires double the accuracy to maintain high enough stability and performance. However, once all the technical problems are solved, as the SSD capacity increases substantially, the required unit cost will be reduced accordingly.

4. Capacity

Toshiba’s QLC technology can already achieve a capacity of 768Gb (96GB) per flash memory particle, which is a greater improvement compared to the 512Gb of TLC particles. If 16-particle packaging is used, a single chip package can achieve a capacity of 1.5TB, which is the largest single chip currently. If an SSD uses eight of these new products, the total capacity can reach an astonishing 12TB.

Written at the end:

What are QLC flash and TLC flash?  What is the difference between QLC flash memory and TLC flash memory?

Although QLC flash memory has just formally appeared in people’s sight at present, it may be inferior to TLC in terms of speed, lifespan, and stability, but the advantages of cheaper cost and larger capacity cannot be ignored. With the continuous development and maturity of technology, it will be sooner or later that QLC is never accepted to be widely recognized just like TLC.

In fact, whether it is TLC or QLC, as long as the price is cheap enough, the capacity is large enough, the speed is fast enough, and the life span is guaranteed, it will always be liked by consumers and win their own market share.

For HDD, the emergence of QLC will bring a greater threat. Perhaps the time when QLC SSDs become popular is when HDDs say byebye to us.

The Links:   2DI75M-050 2SB1260T100R

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