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

84 Comments

View All Comments

  • Death666Angel - Tuesday, October 09, 2012 - link

    The Samsung 830 is the 7th cheapest SSD (based on €/GB) I can find on my go-to price comparison website. 3 of the six before it are much slower Kingston/OCZ drives and the other 3 have SF controllers. Considering the kind of inconsistent performance that delivers and the track record, I would go with the Samsung all the time.

    Now, the 840 just launched and the pricing here is 25% above the 830. But it isn't even available for shipping anywhere. So I don't think that your comparison based on the Vertex4 ship has been shipping for months has any relevance. Also, aren't the Vertex4 numbers with their turbo-mode enabled which stops working after filling the drive to 50%? The Vertex4 256GB model costs 175€, the Samsung 830 256GB model costs 148€. Do you really think the 840 will be more expensive than the 830 in a couple of months? And even so, do you think the Vertex4 if that much better for consumers than the 830? I just don't see it.
    Reply
  • Blazorthon - Monday, October 29, 2012 - link

    Actually, the slowing down after 50% and such for Vertex 4 was fixed in firmware 1.5. The current numbers don't rely on Turbo, they're all the time.

    Also, to all of you, Vertex 4, unlike its predecessors, uses a Marvell-designed controller. Anyone who's used a Crucial or Plextor SSD probably knows that Marvell based SSDs are about as reliability as you can get, up there with Samsung and Intel. Vertex 4 is OCZ's most reliable SSD to date by huge margins, especially with current firmware where it rivals even Samsung and the others in reliability unlike the original firmware (which was specifically stated to be in beta, so anyone who bought Vertex 4 around launch time without doing their research and finding that out probably isn't someone who should be allowed to buy their own SSDs without expert help).

    Also, IDK about UK prices, but in the USA, the Vertex 4, Samsung 830, Samsung 840, and occasionally also the Crucial M4 and Plextor M5S are all at about the same price points for 64GB, 128GB, and 256GB capacities right now. As someone who has experience with Vertex 4, I'd definitely recommend it over Samsung 830 and Samsung 840 so long as it's not more expensive.
    Reply
  • Assimilator87 - Monday, October 08, 2012 - link

    How come the OCZ 4 series just suddenly disappear when the review gets to the power consumption tests? Reply
  • JarredWalton - Monday, October 08, 2012 - link

    Because Kristian imported the results from SSD Bench for the "1.4 Firmware" for the OCZ drives, and when those were retested Anand didn't add in power use figures. I've added them to the graphs using the original power figures at release. Thanks for the heads up! Reply
  • Coup27 - Monday, October 08, 2012 - link

    Excellent article Kristian, enjoyed it.

    Some constructive criticism, although I appreciate that English is not your native language. Sentences aren't that clear when you use a double negative, such as "I wouldn't find it unlikely...". It would be much clearer if you had wrote "It would be likely..."
    Reply
  • Kristian Vättö - Monday, October 08, 2012 - link

    Point taken, thanks for the feedback :-)

    Some things sound logical in my ears but they may not make much sense for a native speaker. I guess this is partially because in English exams and stuff, using more difficult sentence structures (like double negative) will yield higher scores, even though they are not commonly used by natives. Will try to pay more attention to this in the future.
    Reply
  • Sufo - Tuesday, October 09, 2012 - link

    I don't know if I agree with this. While double negatives are certainly inappropriate in some situations, the example you give is nit picking. Add to that, there is a subtle (albeit not technical) difference between "I wouldn't find it unlikely" and "I would find it likely". I accept that had Kristian made a legitimate grammatical error, then correcting it (while a little pedantic) may have been justified, but simply editing for style seems unnecessary.

    I guess my point is Kristian was not objectively wrong, or even unclear (although admittedly, complexity for complexity's sake benefits no one) and so he shouldn't pay too much heed to comments like this simply because OP is an English speaking native and he is not. I am, however, confident that he's more than capable of coming to his own conclusions on the matter :P
    Reply
  • smartthanyou - Monday, October 08, 2012 - link

    I am probably in the minority on this, but as a matter of policy, I don't think you should call anything a review without pricing and a approximate release date.

    Particularly the price. If I don't see a price, I don't bother to read the article.
    Reply
  • sean.crees - Monday, October 08, 2012 - link

    Price is on the 5th page labeled "The Samsung SSD 840" about half way down.

    Although i noticed the price for the 840 250GB is the same as the 840 Pro's 256GB? Is this a typo? Why would anyone buy the non pro with 6 less GB and slower speeds for the same price?
    Reply
  • JarredWalton - Monday, October 08, 2012 - link

    What price are you looking at? The table shows $199.99 for the 250GB Samsung 840 (MSRP) and $249.99 for the 256GB Samsung 840 Pro. Reply

Log in

Don't have an account? Sign up now