Ssd disks with tlc vs mlc memories

The great flash memory boom occurred between 2004 and 2005, when a combination of two factors caused prices per megabyte to drop rapidly. Where smartphone and SSD disks began to notice a reduction, but only the passage of time has made us have more attractive prices, although lately it seems that they are not because of the work and they raise prices again. Do you want to know the difference between TLC vs MLC memories? We explain everything you need to know!

Index of contents

SSD drives with TLC vs MLC memories

The first was the brutal increase in production and competition among manufacturers, which have pushed prices down. In addition to giants like Samsung and Toshiba, even Intel and AMD have invested large amounts of money in the manufacture of flash memory.

The second was the introduction of MLC (Multi-Level Cell) technology, where each cell went on to store two bits instead of just one. This was possible thanks to the use of intermediate voltages. MLC technology has been implemented more or less simultaneously by various manufacturers, and has reduced the cost per megabyte by half, but instead it has resulted in flash memory chips with lower performance and degrading more quickly..

Today, MLC chips are the ones used in the vast majority of USB sticks, memory cards, and SSDs. Traditional chips, which store one bit per cell, came to be called “SLC” (Single-Level Cell), and are produced with the aim of serving the market for high-performance solid state drives (especially models intended for the server market). Although much more expensive, they offer better performance and are more durable.

At the other extreme, we have units equipped with TLC chips, which store three bits per cell, rather than two like MLCs, and therefore reduce manufacturing cost per gigabyte by more than 33%. On the other hand, the use of more intermediate voltages results in chips that degrade faster than MLCs.

Differences between MLC and TLC

In truth, there are no physical differences between the cells on an MLC and TLC chip. In both cases, the production technique is almost the same but there are differences in them… but also the way the chip is programmed. What makes MLC and TLC chips cheaper than SLCs is a simple matter of arithmetic: A 16 gigabyte NAND chip can give rise to a 16 gigabyte SLC chip, a 32 gigabyte MLC chip, or a TLC chip of 48 gigabytes.

Assuming the total cost of the chip is $ 24, we would have a cost per gigabyte of $ 0.75 on the MLC and only $ 0.50 on the FTA. If you are a manufacturer interested in selling large capacity SSDs for a low price, it would be obvious which of the two options would be more attractive to you.

The big problem is not only durability, but also the performance of the chips themselves, which declines with the use of more bits. A read operation that takes 50 µs on an MLC chip will take 100 µs or more on a TLC chip.

At the same time, a write operation that takes 900 µs or more on an MLC chip takes more than 2000 µs on the TLC, resulting in drops proportional to the read and write speeds of the drives.

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The biggest problem, however, is durability. The lifespan of MLC chips is only 10, 000 cycles in the 50nm, while in TLC chips the lifespan is 2, 500 operations in the 50nm.

Even with the use of sectors and other techniques employed by current drivers to extend the life of the drives, a 128GB SSD based on the 25nm TLC chips will carry only 96TB of recordings throughout its lifetime, limiting its use very much. For comparison, a 128GB disk based on 34nm MLC chips will carry 640TB on disk.

An MLC disk would have a relatively low lifespan, but still acceptable if we consider the great advantages that flash memory offers in other areas. The TLC drive, however, would have limited use and in many use situations could be depleted after several years. I mean, they're not bad, okay? But they are of poorer quality.

An SSD with TLC memory is totally suitable for a normal user. But an MLC has higher quality, and they are present in the manufacturers' top of the range.

Many manufacturers have been able to compensate for this drop in flash memory performance and reliability with better drivers and the use of a higher percentage of the SSD, but that does not negate the central question that manufacturers are producing worse flash memory chips. with each new generation, making progress only in relation to cost.

Multi-Level Cell (MLC)

MLC is the standard used by most solid state drives today. The acronym stands for Multi-Level Cell, and is used to describe NAND flash memories that have the ability to store 2 bits of data per cell.

TLC is an evolution of this technology, and allows to store 3 bits of data per cell, while the Single-Level Cell (SLC) stores only one bit of data for each cell. Each one has advantages and disadvantages, which we will see next.

The MLC type is quite common today, and consists of a process that uses differentiated voltages to make a memory cell store two bits (in theory, it is possible to make it store more) instead of just one, as in the SLC.

Thanks to MLC technology, the costs of flash storage devices have decreased, even increasing the offer of products such as USB sticks and smartphones with more affordable prices.

Triple-Level Cell (TLC)

The name itself indicates it: the TLC type stores three bits per cell, therefore, the volume of data that can be stored in the unit increases considerably. It is the most recent standard we have on the market.

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However, the performance is also lower compared to MLC technology, after all, we get eight possible values ​​with three bits, which is why there are more variety of voltages: 000, 001, 010, 011, 100, 101, 110 and 111.

Here, the main benefit is the increase in storage space, since TLC memories are usually slower than MLC chips, which, in turn, have less performance than SLC technology.

Even so, TLC and MLC memories are faster than hard drives, which is why their use is viable in most applications: in many situations, it does not compensate to have a fast SSD, but it does not offer a capacity of enough storage.

What are the advantages and disadvantages?

The great advantage of solid state drives with TLC technology is in their lowest price. This is because the drives with the technology are denser, storing more data with the same amount of space. In other words, they end up having a higher cost efficiency. But this, like everything in life, comes at a price.

Solid state drives with TLC technology end up not being as fast or as durable as MLC models. Therefore, they are not indicated for professional use.

Indeed, TLC solid state drives are better suited for home users. For these types of users, there is no noticeable performance difference, at least in the vast majority of cases.

How many recording cycles do you support without losing your ability to store data?

It is clear that the number of write cycles supported by a cell affects its useful life. But fortunately, it is not the only factor. There are two others of great importance: the frequency with which the value contained in the cell is modified (the frequency with which it is read has no influence on the useful life) and the capacity of the mass storage unit (in our case, from the SSD or solid state device) in which it is installed.

The importance of the frequency of recording operations is obvious: the frequency of writing operations in a cell that supports ten thousand write cycles of a little used unit or that stores static data is small. This cell, therefore, will last much longer than the other, installed in a drive that is used to store dynamic data whose values ​​change often and must be rewritten at all times.

As important as the memory bank where the data is stored on an SSD is the controller contained within it, which functions as an interface between the SSD disk and the computer. This is the controller that decides in which cells the data will be stored.

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During these last years in which SSDs have been spreading, the algorithms that determine what these cells will be have been perfected. Newer controllers seek to distribute the read operations of the cells available on the SSDs as homogeneously as possible, preventing some cells from receiving much more write operations than others.

In the early days of using SSDs, drives were relatively small in capacity. 1TB drives are readily available today. Well, if the total number of cells into which write operations can be distributed is greatly increased, the frequency with which each cell is overwritten is reduced in direct proportion to this increase.

Hence the importance of the capacity of the SSD as regards its longevity. But still, MLC-based devices have a much shorter lifespan than SLC-based ones.

Another important difference is the speed with which write operations are performed. Although this time, the read operations do not interfere. After all, to measure a voltage it is enough to apply a sensor to the points where there is a difference in electrical potential. But in the case of writing, the thing is different.

This type of memory cell, as can be seen, can store eight different values ​​(000 ₂ = 010 to 1112 = 710). The simple observation is sufficient to show that "writing" a value (adjusting the voltage level) is much more complicated (and therefore slower) when the number of possible values ​​increases. And, by increasing the voltage range, energy consumption increases.

Temperature issue

Until recently, memory modules dissipated heat, but this was never a concern. However, when it comes to multi-level flash memory, it is different.

After all, they operate at high frequencies and use relatively high voltages, two important factors when it comes to heat dissipation, and therefore increased chip temperature.

This is especially delicate when it comes to MLC memories, where the number of thresholds of internal voltages that identify the stored value is greater.

This is because too high temperatures can interfere with these thresholds, which modifies the stored value and completely compromises the reliability of the memory.

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The result is that it is definitely not advisable for the bases of this type of memory to be kept at very high operating temperatures. For this reason some devices (for example, some Samsung SSDs) have temperature sensors that simply slow down the writes (the readings, as always, have little effect on heat dissipation) in cases where temperatures above 70 degrees Celsius and only return to normal operation when banks cool to below this limit value.

Single-level memories (SLC) are much more tolerant of high temperatures. This is because because it can take only one of two states, the tolerance is much greater than the temperature changing the voltage threshold slightly, so the stored value does not change.

Thus, single-cell SSDs, more expensive but withstanding higher temperatures, are classified as "industrial", while MLCs, which must operate in a lower temperature range, are classified as "commercial".

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conclusion

The MLC has a longer useful life than the TLC, because it is easier to distinguish the 4 possible voltage states than the 8 that have a smaller margin of error. This is also why a TLC SSD is cheaper and we find it in low and medium range SSDs.

We now know that MLC memory-based SSDs are more expensive than TLCs, withstand lower data density, are faster, and can withstand higher temperatures, with a longer lifespan and consume less power. What do you think of everything? You already tell us your impressions, after reading the article!