How a MicroSD Card Can Store Up to 400GB of Data

On 31 August 2017 SanDisk announced a massive storage capacity microSD card, capable of fitting 400 GB of data onto it. That’s right! A memory card the size of a penny can cram an incredible 40 hours of raw 1080p video, something that was absolutely incomprehensible to technology experts a mere decade ago. But is this really the upper limit? Have we reached peak memory? Or can we fit even more into this tiny 5-square-millimeter space?

A Theoretical Problem


A half a centimeter doesn’t give you a whole lot of space, and devices that are manufactured for microSD cards cannot be repurposed to fit something else. This means that you’ll have to work within these constraints. Usually, card manufacturers like SanDisk would shrink the size of their transistors so more of them fit into the tiny space. In 2013 this size was roughly 19 nm. One sheet of these transistors within a half-centimeter space would yield 8 GB of storage space, which was plentiful for most small-scale consumer devices.

To make more memory fit into the same amount of space, you would need to stack the transistors on top of each other, creating transistor layers that would double or quadruple the amount of storage space available to you. That is how microSD cards with 32 GB capacities began to appear. There comes a point in time, though, where things get a little too cozy and you have to start eating at the frame to fit more layers.

At the 19 nm level, you would need eight layers of transistors to fit 64 GB of memory. To fit 400 GB, you’d need exactly fifty layers. While this is theoretically possible, it’s extraordinarily difficult to do in such a confined space.

When There’s No Choice But to Double Down


We already discussed the fact that it’s just not feasible to change the dimensions of every slot on every device to fit a bigger card. The only option left is to dive even deeper into microtransistor manufacturing technology. We have to make them smaller!

Theoretically, a transistor could be as small as a single molecule. On the 14th of August, we’ve actually managed to make single-molecule transistors that operated sustainably at room temperature. Because the process of making these is so convoluted, we can’t expect them to go mainstream anytime soon, but it presents a window into what the future looks like. We may soon see transistors measuring as little as 5 nm.

Remember, transistors fit in a three-dimensional space, meaning that as you make them smaller, you also get more space to stack them. This is what must have happened for SanDisk to be capable of creating a 400 GB microSD card. Under the 10nm transistor specification available to manufacturers as of 2017, you can fit 400 GB of memory using 25 layers of transistors that can now fit roughly 16 GB per layer.

With 5nm transistors, we could end up creating microSD cards that fit a terabyte of memory, which is roughly where I see the limit. We might not be able to surpass that level and probably won’t even need to for the foreseeable future.

Do you see any need for more than 1 TB of memory (let alone 400 GB) in a microSD format? Tell us your thoughts in a comment!

Miguel Leiva-Gomez Miguel Leiva-Gomez

Miguel has been a business growth and technology expert for more than a decade and has written software for even longer. From his little castle in Romania, he presents cold and analytical perspectives to things that affect the tech world.


  1. I don’t see the need to go beyond 1TB of space, but as long as you can get a device – smartphone, tablet or laptop – to address that on a microSD card, what a wonderful and easy way to upgrade the storage of that device!

    I anticipate, however, that cards at those high capacities will be very expensive for at least a year or two. When they start to come down in price, I think you’ll see a lot of consumers purchase cards at those high levels.

    1. “I don’t see the need to go beyond 1TB of space”
      That sounds very much like the statement blamed on Bill Gates – “640K Ought to be Enough for Anyone” /grin

      1. Interesting, though, isn’t it? That we are exceeding general storage requirements for most of the market with regards to microSD cards. 20 years down the line, if this format still exists, we will have to figure out a way to go beyond the limits we see, perhaps using new materials. But the problem is that there is a physical limit to how far we can push transistor size: Molecular/atomic level. So, we will have to either learn how to store things in less space or we will have to change formats for larger volumes.

  2. I already have difficulty with most devices being able to read a 128GB card. Which devices will read these?

    1. I expect that can be fixed with a firmware update, if not now – soon. Either that or a well coded memory management application. Those are a few of the ways they got past the 4 mb RAM limits back in the day.

      1. Firmware updates cannot solve hard-coded bit widths. Some devices will simply not be able to read the entire address space on these cards, no matter what you do.

  3. I can only imagine how expensive these cards will be. Wouldn’t it be easier and morw cost-effective just to swap out the card when it is full?

  4. I doubt about the reliability and the accessing time being too long problem! Cheers

  5. I don’t see the need 1TB of space, when our smartphone not smart enough to install application from phone memory to microSD card.

  6. Yey. This would make my Raspberry Pi the full equal to many laptops. It is also great news for photographers and small portable video cameras. Much more storage before my car cam loops, weeks instead of hours, or perfect for storage on remote game cameras. I can think of many many uses just off the top of my head. And yes I actually remember my desktop that had a whole 8 megabytes and I had to change 8 inch hard drives to change applications.

  7. It’s mind-boggling stuff. What then is the difference between such a 400 GB micro SD card and an SSD of similar capacity?

    1. The main difference, in short, is that they have different controllers. SSDs are more intelligent. I will get to this soon!

  8. What about the reliability of such cards ? Correct me if I’m wrong but the smaller the size of each cell, the more it can be corrupted by small changes (electrical, magnetic or phusical shock, for instance)

    1. Absolutely! The write-cycle lifetime ultimately dictates how many times you can add to/remove information from an SD card before it goes kaput, but the reliability of said card will be about the same as a smaller one, to be completely sincere. Transistor size should not really affect its reliability since it operates under the same concept and uses the same enclosure. So any sensitivity a larger transistor has would be reflected 1:1 on a smaller one.

  9. The larger cards seem to be electrically more fragile in my experience. My 128GB lasted less than a year with an abrupt failure causing it to get red hot and lost most of its data, reading abnormally low resistance on the longer power pins.

    Had the same syndrome on a 64GB possibly related to a dodgy card reader but never proved this conclusively.
    They seem to do this if the internal regulator goes bad which is handy for data recovery (run at lower voltage)

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