A TLC Refresher

Back in February, we published an article called Understanding TLC NAND, where we went in-depth about how NAND works and the differences between various kinds of NAND (SLC, MLC, and TLC). Back then we didn't know when TLC SSDs would be publicly available or who would be the first manufacturer. Supposedly, OCZ had interest in releasing TLC based SSDs but the supply of TLC NAND wasn't good enough for their needs. Samsung has the benefit of being a tier one manufacturer that makes its own NAND, which gives it an advantage when dealing with new technologies as it can control the output of NAND. In this case, Samsung was able to ramp up the production of TLC NAND when it wanted to, whereas OCZ must live with whatever the NAND manufacturers are ready to sell them.

While we have covered TLC in detail already, we have some new details to add:

  SLC MLC TLC
Bits per Cell 1 2 3
P/E Cycles 100,000 3,000 1,000
Read Time 25us 50us ~75us
Program Time 200-300us 600-900us ~900-1350us
Erase Time 1.5-2ms 3ms ~4.5ms

Samsung would not tell us the exact read, program, and erase latencies but they told us that their TLC is around 50% slower than their MLC NAND. We don't know the latencies for Samsung's MLC NAND either, hence we have to go by general MLC NAND latencies, which varies a lot depending on process. However, we were able to get the P/E cycle count for TLC, which is 1,000. Samsung did not specify the process node but given that they listed MLC at 3,000 cycles, we are most likely talking about 27nm or 21nm. I wouldn't find it unlikely that Samsung is rating their 21nm MLC NAND at 3,000 P/E cycles as well because IMFT was able to keep the endurance at the same level with their 20nm MLC NAND.

Physically, TLC is similar to SLC and MLC. All three consist of similar transistors, the only difference is that they store a different amount of bits per cell. SLC only stores one, whereas MLC stores two and TLC stores three. This actually creates a minor problem, as there is no multiple of three that is a power of two. Unlike with hard drives, SSD capacities typically go in powers of two, such as 64GB, 128GB, and 256GB.

NAND is actually built based on binary prefixes (Mebi, Gibi...) but is almost always referred to using metric prefixes (Mega, Giga...). For example a 128GB SSD has ~137.4GB of storage (128GiB) due to Gibi to Giga translation, but the remaining space is used as spare area.

If the raw NAND array has 17.2 billion transistors, you would get 16Gibibits (17.2Gbits) of storage with SLC NAND because each cell can store one bit of data. MLC yields 32Gib, which is still a nice power of two because all you're doing is adding one level. However, with TLC you get 48Gib, which is not a power of two. Technically nothing is stopping manufacturers from making a 48Gib die, but from the marketing and engineering standpoint it's much easier to stick with powers of two. A TLC die in this case should be 32Gib just like MLC. To achieve that, the die is simply reduced in size to around 11.5 billion transistors. 32Gib isn't exactly divisible by three, but thanks to spare bits it doesn't have to be. The trick here is that the same capacity TLC die is smaller than an MLC die, which results in more dies per wafer and hence lower production costs.

Introduction Lower Endurance - Why?
POST A COMMENT

85 Comments

View All Comments

  • Impulses - Monday, October 08, 2012 - link

    At one point in the article you mention 830 users would at least wanna upgrade to the 840 Pro if they aren't gonna wait for next gen drives... I kinda thought the Pro qualified as next gen, with the vanilla 840 being more of a side grade from current gen drives. So what would you consider or expect from a next gen drive? Reply
  • KAlmquist - Tuesday, October 09, 2012 - link

    One thing I've been wondering is what voltage the controller uses. I can't identify every component on the board, but I don't see anything that looks like a voltage regulator. It seems kind of crazy to run a chip with three processor cores at 5 volts, but I guess it's possible. Reply
  • Death666Angel - Tuesday, October 09, 2012 - link

    Loved the review. I'm really looking forward to more data on the DSP usefulness inside SSDs, could be a huge advantage (though I don't worry about going through my P/E cycles at home).

    With SSDs, we are at a point similar to GPUs and CPUs where I don't understand upgrading from generation to generation. Unless you have a very specific usage case and can make great use of the better speed (video/picture editing or something equally I/O intensive), I don't think a 840 Pro will feel that much faster than a 830.
    I'm still rocking a first gen Agility 60GB in my (ULV) notebook and a Vertex2 120GB in my desktop and they feel plenty fast, especially those times when I'm at a friends PC with only mechanical storage.
    I might upgrade to a 830 or 840 (non Pro) when the prices have dropped for the 830 or stabilized for the 840 (I don't like paying for launch pricing). :D

    And I finally got my brother to go to SSD storage, too! He'll either get a 512GB 830 or 2x256. Does anyone know why 256GB usually has the best price/GB instead of the 512GB drives? Considering the cost for casing, PCB, controller etc. stays the same, I would expect the 512GB to have better pricing/GB. Do they need to go with more dense packages which are more expensive?
    Reply
  • name99 - Tuesday, October 09, 2012 - link

    I agree completely.

    I've said before that the current emphasis on performance over everything else is as stupid as Intel's Pentium4 philosophy. Devices have to become more balanced if they want to sell better.

    In particular the current atrocious write power draws for these devices mean that they will not sell in the external drive market --- they can't be fully powered by USB2 and
    - no-one wants a drive that needs two USB connections because it's clumsy and it uses up limited USB slots
    - saying it can be fully powered by USB3 is not good enough because, for the near-term future, people want to share drives between USB2 and USB3 computers.

    Of course MOST, but not all, the external drive market is about capacity, not speed. However each time SSD capacity doubles, a larger portion of the external drive market makes sense; AND power is not only an issue for the external market. The higher you set your peak power draw, the less your flash appeals to Ultrabook manufacturers.

    Just remember Pentium 4 and its power draw, and compare to Intel trying to get Haskell to run at <10W nowadays. Balance matters, and current flash manufacturers seem to be far too unbalanced compared to the requirements of most users.

    (It would be fascinating, for example, if we learn that the flash in the next round of iOS devices, or even MacBooks, was designed in-house by Apple because they were not satisfied with the power vs performance choices that were being made by the major flash manufacturers. Remember --- Apple bought Anobit...)
    Reply
  • moadip - Tuesday, October 09, 2012 - link

    does the 830/840 family support AES encryption? Want to buy one of those but there is no official word on any support for this. Is anyone of you guys/girls using them in that way? Reply
  • Kristian Vättö - Tuesday, October 09, 2012 - link

    840 and 840 Pro both support 256-bit AES encryption Reply
  • moadip - Tuesday, October 09, 2012 - link

    what about the 830? Reply
  • Kristian Vättö - Tuesday, October 09, 2012 - link

    I'm not 100% sure but as far as I know, only the OEM/enterprise version (i.e. PM830) supports encryption, the consumer 830 doesn't. Reply
  • MrSpadge - Tuesday, October 09, 2012 - link

    What an amazingly well balanced drive! Currently it's more expensive than the 830 at similar capacities, but as soon as 21 nm yield ramps up (and prices are adjusted) this will probably be one of the best or maybe the best consumer SSD on the market. Reply
  • iCrunch - Tuesday, October 09, 2012 - link

    Thanks for another tremendous AnandTech review! You guys are insane! ;-)

    I own a 256GB Samsung 830 as part of my Retina MBP and I must say, I'm blown away! My first SSD was an Intel X25-M G1 80GB and through the years, I've had the fortune to own several solid state drives, including the OWC Mercury Extreme Pro 6Gbps, a couple of Intel 520's in RAID 0, the Samsung 470 as well as pre-470 Samsung OEM models. Thanks to this review, I'll be going for the 840 Pro as soon as soon as I can justify getting another desktop or laptop. Decision made!

    I'm used to high SSD pricing, so if the 840 Pro 256GB will be going for $250 or less, count me in. If the downward trend of SSD prices really does continue, or, even better, if a breakthrough drive like the 840 series with its less expensive TLC NAND appears to be, I'd love to start getting 512GB drives. Black Friday, here we come...
    Reply

Log in

Don't have an account? Sign up now