To USB or Not to USB


Does my NAND need USB 3.0? – Types of NAND by Application – Part 3

NAND flash is the basic component in USB Flash Drives, SD Cards, SSDs as discussed in the first blog.

As discussed in the second blog, NAND flash is only one compenent that affects overall USB throughput.

Based on feedback from readers, I’m going to go back to the basics on NAND.  For even seasoned Semiconductor professionals, this might be useful.


Basics Review

  • NAND is non-volatile (permanent) storage. 
  • NAND is a chip (no moving parts like a Hard Drive)
  • NAND chips can be of different quality, speed, or capacity
  • Multiple NAND chips can be used together to make a larger storage product
  • NAND chips go into USB flash drives, SD Cards, SSDs …


NAND chips used in USB Flash Drives, SD Cards, and SSDs are  different

Why are they different?

  • Each type of product has different requirements.
    • Cost
    • Performance
    • Capacity
    • Read/Write Frequency and Durability

The characteristics required by each market segment are summarized below:

Memory Slide


Please note the $ per GB data is my estimate based on a review of prices at


Let’s talk about this based on Market Segments starting with USB Flash Drives


USB Flash Drives

Users use USB Flash Drives

  • for temporary storage, for example for file transfers
    • Power point presentations in a meeting or
    • Photos handed to a friend
  • Typically Flash Drives are not used for long term storage
  • Consumers expect low prices

What isn’t written about much is USB Flash Drives tend to have few read and write cycles.  This means the USB Flash drive does not need to be able to handle 10,000 plus cycles of read and write.  So the NAND used in a USB Flash drive can be cheaper.


Looking at the table above, there are 2 market segments for USB Flash Drives:  Low Cost or High Performance

I would expect that the Low Cost drives have slow NAND flash and only be rated for 100s of read/write cycles.  This means it will fail sooner than a more expensive drive.  I suspect that you have either

a) Already experienced a data lost or a corrupted USB Flash Drive or

b) Lost the Flash drive before this could happen

I would expect High Performance USB Flash drives

1) have faster NAND chips to actually read and write faster.

2) Have read/write cycles up to 1000 times.


If you are using a USB 3.0 Flash Drive like the Lexar Triton 32GB unit I tested and recommended, I would expect this to have a much higher read/write cycle endurance but I don’t have data to support this.  You might use this to transfer video data between work stations and multiple people work on the same data.

Also, it would be handy for moving around certain debug info fast between work stations, rather than going through a network.


Conclusion 1 for USB Flash: If you build USB 3.0 for High Performance, you use USB 3.0.  If you use USB 3.0 you use faster NAND.   Since you are building products that will ship in mass production in 2014, you should plan to build your USB 3.0 Flash Drives with fast NAND, or it just won’t be competitive.  

Conclusion 2 for USB Flash: Within 2 years USB 3.0 will become ubiquitous, if you are in the low cost market the only questions to ask are:

  • Where are you going to compete? 
  • Will your product still be able to sell in 2 years if it uses slow NAND with USB 2.0?
  • Can you maintain even a few pennies of profit if you ship cheaper, slower NAND, if no one buys it?
  • If yes, what volumes can you ship?
  • What can you ship when competing against other low-cost providers?
  • Do you want to play in this market of slow, cut-throat USB Flash drives?

SD Cards

I’m sure you use SD cards in your digital camera. 

There are 3 major classifications of SD including

  1. SD
  2. SDHC or (Secure Digital High Capacity)
  3. SDXC or (Secure Digital eXtended Capacity)

Usually, the cheapest o these cards will only be labeled SD

SD Speed Classes

    • There are No Class (like me) cards that have no class designation.  You won’t know what speed these cards are until you actually try them.
    • Then there are Class 2, 4, 6 and 10.
    • Class 10 memory must operate at 10 MB/s or more
    • Class 2 memory operates at 2 MB/s or more
    • You get the idea.

You can expect that all SDXC cards will be Class 10 cards.

Most SDHC cards will have a rating.  A faster Class 10 card will cost more than a slower Class 2 card (for the same memory capacity).

Sidenote: There are 3 different form factors, the largest one (the blue one below) is used in most cameras, the microSD you might use in your Blackberry to increase the storage space for photos or music.

File:MicroSD MemoryCard 002.jpg

Different SD Card sizes – From Wikipedia


Back to pricing, as you can see from the table SDHC is the cheapest in terms of cost per GB of data.

Here’s 2 examples of SDXC cards from


This is interesting because many consumers:

  1. Remove the SD card from their camera
  2. Insert it into their laptop SD card reader
  3. and read the data directly.

These cards are 45 MBps and 95MBps read speeds but

“…many SDHC readers are connected internally through a USB 2.0 bus, which does not have enough bandwidth to support SDXC.” from this article on SDXC.


This means that USB 2.0 can’t keep up with the speed of the SDXC.  You need to upgrade you SD Card Reader to support SDXC and therefore you need to upgrade to USB 3.0 to read these cards.

Another good reason to adopt USB 3.0 and USB 3.0 Card Readers.


If you buy a lot of SD memory, you probably know that SDHC is sweet spot for buying memory.  The cost per GB of data is the most attractive.  Most cameras do not need anything faster than Class 10 for recording pictures when you take pictures.   You want faster read speeds when transferring them to your PC because you’ve taken about 8 GB of photos each time you go to an event.

Conclusion 1 for SD: SD Cards need NAND only rated for 100s of read/write cycles.  But SDXC cards come closer to being additional, semi-permanent additional memory.  (Plug it into your PC to expand the memory available on your laptop.)  This means SDXC NAND must not only be faster, but handle 1000s of read/write cycles.

Interestingly, this may also explain one reason NOT to put an SD Card Reader into a Tablet PC until SDXC memory is proven to be reliable for continuous use for data reading writing.   If your SDXC card failed and your last 3 years of photos were on that card, you might get angry at the tablet maker.

Conclusion 2 for SD: You need to have a USB 3.0 Host in your system to support USB 3.0 to SDXC card readers.  Although SDHC is the sweet spot now, in 2 years the sweet spot will continue to more to faster SDHC, and SDXC which REQUIRES USB 3.0.  If you want your product to appeal to the high-end customers who have the most disposable income to spend, you must build your product with faster NAND, or with products that can read the faster NAND in this case SDXC.




Next Time



Blogger Comment and My Comment

I received a comment on a blog that read “What will my 2014 Lunch be?”

I didn’t understand this.  However, I am sure that you don’t adopt USB 3.0, someone else will be eating your lunch.


I am all out of Funny this week.
Send me something funny.

  • Please.
  • Pretty please.
  • I need help.
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