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Everything You Need to Know About SLC, MLC, & TLC NAND Flash

Everything You Need to Know About SLC, MLC, & TLC NAND Flash
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Synopsis: This guide outlines the differences between SLC, MLC, and TLC NAND flash, explaining the pros and cons of each, to help readers choose the right SSD when upgrading.

Anyone who's tried one will attest, solid state drives (SSDs) sure are great! With faster load times for your favorite apps, higher overall efficiency, and added durability compared to traditional spinning hard drives, it's no wonder they're popping up in every new device that hits market.

But what makes certain SSDs more expensive than others? Like race cars, it's all about what's under the hood.


Quick Links


The Anatomy of an SSD

MyDigitalSSD BP4e mSATA SSD

MyDigitalSSD BP4e mSATA SSD with two enclosed NAND flash memory chips installed. The controller chip is designed by PHISON

  • A. NAND Flash: The part where your data is stored, in blocks of non-volatile (does not require power to maintain data) memory.
  • B. DDR Memory: Small amount of volatile memory (requires power to maintain data) used to cache information for future access. Not available on all SSDs.
  • C. Controller: Acts as the main connector between the NAND flash and your computer. The controller also contains the firmware that helps manage your SSD.

What is NAND Flash?

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. How those on/off cells are organized represents 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.

The reason behind SLC only being available at lower capacities is down to the physical real estate the NAND flash occupies on the Printed Circuit Board (PCB). Don't forget that the circuit board has to have the controller, DDR memory, and flash built to standard dimensions to fit inside your computer. MLC doubles the amount of bits per cell, whereas TLC triples, and this opens up for higher capacity SSDs.

There are particular reasons why manufactures build flash memory with a single bit per cell like SLC. SLC has the advantage of being the fastest, most durable but has the cons of being more expensive, and is not available in higher gigabyte storage capacity. That is why SLC is preferred for heavy enterprise usage.

MLC and TLC flash in comparison to SLC, is cheaper to produce, available in higher storage capacities, but at the tradeoff of relatively shorter life spans and slower read/write speeds. MLC and TLC are preferred for everyday consumer computer usage.

Understanding your own needs for computing and NAND flash basics will not only help you pick the right SSD, but will also help you figure out factors such as the price behind the product.


SLC (Single Level Cell)

The Single Level Cell flash is so called for it's single bit that can either be on or off when charged. This type of flash has the advantage of being the most accurate when reading and writing data, and also has the benefit of lasting the longest data read and write cycles. Program read/write life cycle is expected to be between 90,000 and 100,000. This type of flash has done exceptionally well in the enterprise market because of it's life span, accuracy and overall performance. You won't see too many home computers with this type of NAND due to its high cost and low storage capacities.

Pros:

  • Has the longest lifespan and charge cycles over any other type of flash.
  • More reliable smaller room for read/write error.
  • Can operate in a broader temperature range.

Cons:

  • The most expensive type of NAND flash on the market.
  • Often only available in smaller capacities.

Recommended for:

  • Industrial use and workloads that require heavy read/write cycles such as servers.

eMLC (Enterprise Multi Level Cell)

eMLC is MLC flash, but optimized for the enterprise sector and has better performance and lastability. Read/write data life cycles are expected between 20,000 and 30,000. eMLC provides a lower cost alternative to SLC, yet maintains some of the pros of SLC.

Pros:

  • Cheaper alternative than SLC for an enterprise SSD.
  • Has better performance and endurance over standard MLC.

Cons:

  • Does not match SLC NAND flash SSDs in performance.

Recommended for:

  • Industrial use and workloads that require heavy read/write cycles such as servers.

MLC (Multi Level Cell)

MLC flash as it's name suggests stores multi bits of data on one cell. The big advantage of this is the lower cost of manufacturing versus manufacturing SLC flash. The lower cost in flash production is generally passed onto you as the consumer, and for that reason is very popular among many brands. MLC flash is preferred for consumer SSDs for it's lower costs but the data read/write life is less in comparison to SLC at around 10,000 per cell.

Pros:

  • Lower production costs are passed onto you the consumer.
  • Is more reliable than TLC flash.

Cons:

  • Not as durable and reliable as SLC or enterprise SSDs.

Recommended for:

  • Everyday consumer use, gamers, and enthusiasts.

TLC (Triple Level Cell)

Storing 3 bits per cell, TLC flash is the cheapest form of flash to manufacture. The biggest disadvantage to this type of flash is that it is only suitable for consumer usage, and would 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:

  • Cheapest to manufacture which in turn leads to cheaper to market SSDs.

Cons:

  • Cells will survive considerably less read/write cycles compared to MLC NAND. This means that TLC flash is good for consumer use only.

Recommended for:

  • Everyday consumer use, web/email machines, netbooks, and tablets.

The SSD Life Cycle

Like all good things, an SSD does not last forever. As noted above, a solid state drive's life cycle can be directly attributed to the NAND flash it comes with. SLC flash, for example, will last longer than MLC or TLC flash but that comes at a hefty price tag.

With MLC and TLC flash commonly used/found in consumer SSDs, the real question is how long will they last?

TechReport.com has tested several available consumer-grade SSDs, most of which were MLC NAND with one being TLC NAND, and the results are promising. All of the devices tested lasted at least 700 terabytes (TB) of writes before failing, and a couple even pushed passed a petabyte (PB).

This is a lot of data, but let's put that into perspective in writing 1 PB to an SSD.

1 petabyte (PB) = 1,000 terabytes (TB) / 1,000,000 gigabytes (GB) / 1,000,000,000 (MB)

That 1 PB could net you:

  • 222,222 movie DVDs at 4.5GB a DVD
  • 333,333,333 mp3 songs at 3MB a song
  • 500,000,000 jpg photos at 2MB an image
  • 15,384 installs of the game Grand Theft Auto V at 65GB an install

Looking at those numbers should really put to rest any doubts about your SSD failing in any short amount of time.

If you are considering an MLC or TLC SSD for everyday consumer use like; storing music, photos, software, personal documents or play games then you should feel assured that your SSD should last several years. This kind of usage is considered light compared to the ongoing heavy read/write usage of enterprise servers and computers as outlined in the next section below.

Note: For anyone worried about the lifespan of their SSD, features such as Self-Monitoring Analysis and Reporting Technology, or S.M.A.R.T. for short, can help you better keep track of your SSD's longevity.


Enterprise vs. Consumer SSDs

Enterprise SSDs are commonly found in database servers.

The difference and demands expected of enterprise SSDs set them a world a part from consumer SSDs. Enterprise SSDs are designed to meet a higher standard, and consistently perform in high-tech services, military, science and any area that would require a large amount of reading and writing data.

Database servers are an example of where you might see an enterprise SSDs, these servers are on 24/7 and that includes: longer read/write life cycle, faster read/write speeds, increased reliability and durability in harsh environments.

Consumer SSDs are less expensive, and are stripped down versions of enterprise SSDs. This may sound like you are missing out on certain features, but the benefits of a cheaper product with larger storage capacity are worth it. Besides manufactures are always increasing the performance of SSDs while bringing down the price.


In Conclusion

At this point, you probably have a good idea on the difference between SLC, MLC, and TLC NAND flash. The basics we discussed here, with insight into why some cost more than others, should clear up any confusion as to what type of flash best fits your needs.

Flash Type

SLC

Single Level Cell

eMLC

Enterprise
Multi-Level Cell

MLC

Multi-Level Cell

TLC

Triple-Level Cell

Read/Write Cycles 90,000-100,000 20,000-30,000 8,000-10,000 3,000-5,000
Bit Per Cell 1 2 2 3
Write Speed ★★★★★ ★★★★☆ ★★★☆☆ ★★☆☆☆
Endurance ★★★★★ ★★★★☆ ★★★☆☆ ★★☆☆☆
Cost ★★★★★ ★★★★☆ ★★★☆☆ ★★☆☆☆
Usage Industrial/Enterprise Industrial/Enterprise Consumer/Gaming Consumer

The important thing to take away from this guide is that modern SSDs are built to last a considerable amount of time. While their life-cycle should be taken into account, it should by no means prevent you from buying faster and more efficient storage.

Comments on Everything You Need to Know About SLC, MLC, & TLC NAND Flash

PJSplace Saturday, January 25, 2020 11:57:56 AM
I have an older gigabyte x58 usb3 with DDR3 24 gibs of Memory installed with the intel i7 cpu I am building, it was given to me with the cooler master fan and CM PS 600, I just need the case, and GPU and SSD's. I am have a hard time finding some to use. First if they fail I would like a manufacture that will work with me, unlike Samsung and Sandisk whom I have read is like pulling teeth, please advice, I would like an SLC but as you say not likely sooooo any suggestion, Prefer just one for the OS and another for games and another for everything else.
MyDigitalDiscount.com:
Your best bet is a 2.5-inch SATA but don't let this blog post scare you away from TLC flash. It's come a long way since we first published this article and that's a big reason why it's used in most consumer drives found on the market today.

MyDigitalSSD offers a Super Boot 2 SATA III 6Gb/s 2.5-inch SSD series that features TLC flash with amazing endurance, backed by an MLC buffer for an outstanding value. MyDigitalSSD also has a personable support staff that can assist you in getting the most from your drive or recommend an external drive if you're still looking for more.

We currently have MyDigitalSSD Super Boot 2 stock on Amazon, here: https://amzn.to/30VeDKb
Andrew Sunday, December 15, 2019 04:30:30 AM
Further to my comments about retailer labeling, it seems to me it's all very well comparing, but unless you build your own it's very difficult to know what's actually in the computer and even if the OS tells you, this well known retailer insists all non drive storage are called SSD and all SSD are basically the same so wouldn't accept a return.

I guess you can fit a different drive in your laptop, but many retailers say this invalidates the warranty.
MyDigitalDiscount.com:
Adding a secondary SSD, or replacing the main solid-state/hard disk drive outright, may void the warranty of the product being upgraded. We urge all of our customers to double-check their warranty and be aware of those risks before modifying their device or PC.
Andrew Sunday, December 15, 2019 04:22:23 AM
Why is emmc not mentioned here? Unless I missed it. I am really confused about the semantics of the non disk storage vocabulary. I was discussing with a retailer who was labeling their laptop as having SSD, where as the manufacturer site said emmc and made a distinction between models as having SSD "OR" emmc, but the retailer insisted that emmc was a subcategory of SSD and SSD was a catch all for any non disk storage, but why does the manufacturer make use of the distinction differently and why are there so many technology articles that compare SSD and emmc if SSD is a catch all term? I thought the catch all term was SSS.

The well known retailer label also said the CPU was Pentium silver, but then said it was n3700 or something but every CPU listing or comparison site I went to there was no listing of what they said was in it under the silver family.

Additionally, this well known retailer also said they get same name models but with manufacturer exclusive internal spec.
MyDigitalDiscount.com:
eMMC is a type of onboard flash and any device or computer using it typically can not be upgraded using the kind of SLC, MLC, and TLC drives we sell.

How-To Geek has a great article about it, here: https://tinyurl.com/ydy5eltc

Without knowing the specifics, when it comes to buying a PC, trust your gut. If something doesn't add up, we generally advise customers to look elsewhere even if it's a great deal from a well-known retailer.
reader Wednesday, October 23, 2019 06:20:57 AM
re previous comment, sounds like you are going by the numbers only. I have a samsung 860 evo, MLC, trust me, it ain't slow and it [so far] works. don't just go by the chart you have in front of you. "only concentrate on slc" is, tbh, cr*p advice.
Michael Nielsen Saturday, October 19, 2019 04:21:42 AM
Slc is clearly the best, so only concentrate on that! And then when they can sell it with a 75 dollar per TB price tag, then go for it.
Jim Monday, October 14, 2019 02:44:48 PM
The information is very helpful. SLC flash is what we would need. The application is very data-intense and many read-writes are performed throughout the product duties.
I also assumed MLC was many-level instead of two-level.
Zach Wednesday, October 9, 2019 06:53:18 PM
Is there any way to test whether a drive is SLC or MLC? Maybe a piece of software that could confirm it one way or the other?
MyDigitalDiscount.com:
CrystalDiskInfo is free software that will tell you the model number of your drive. You can then use that number to search online to confirm if it has TLC, MLC, or SLC flash.

https://crystalmark.info/en/software/crystaldiskinfo/


Unfortunately, the best way to find out is to check the make/model number of your SSD online.
K Wednesday, September 11, 2019 05:39:01 AM
Thank you for the article! Very helpful.
Travis Sunday, July 21, 2019 09:38:15 PM
So, I am looking to buy this cheap entry level wd green ssd. On the website it says to be a SLC ssd but after reading your article I have a hard time believing that it's slc. Can you please confirm it for me. Link for the ssd is attached.

https://www.wd.com/products/internal-ssd/wd-green-ssd.html
MyDigitalDiscount.com:
The WD Green is a TLC drive. SLC caching, as featured on that drive, is not the same as SLC flash. It's a process that is often used to help speed up TLC flash by changing the I/O speed. Another giveaway is the 3-year warranty. SLC flash is commonly warrantied for 5-years.
Lejaune Tuesday, June 25, 2019 11:51:26 AM
I always though in order to store 1 bit, you need two levels, one level represents a '0' and the other level, '1'. I wonder how single level logic can work.


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