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I see microSD cards up to 400GB, as well as SSD up to 400GB.

My question is related to the size: If you can fit 400GB in a microSD card, why do we need the size of a SSD (more commonly, 2.5 in)? What other electronics or components are in a SSD that its size is so much bigger than a microSD, while having same storage?

Giacomo1968
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igorjrr
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    Cards can fail, more so, I think, than quality SSD drives. I use a big, fast SSD drive for my laptop so everything is on one drive. Better that way, for me. – John Aug 13 '20 at 14:49
  • 2.5" SSDs are 'old tech' these days, they are built to a form factor that made them simple to swap into existing 2.5" "laptop size" HD slots in existing computers.. Look at M2 NVMe drives for comparison. – Tetsujin Aug 13 '20 at 14:56
  • SSDs are also an order of magnitude faster than even the fastest SD cards these days. – Sam Forbis Aug 13 '20 at 16:08
  • @Tetsujin true, forgot about the NVMe drives. However they are still much larger than a microSD card with similar size. That was my question: why size matters? What do they have extra (other than storage) that they need to be bigger? – igorjrr Aug 13 '20 at 16:24
  • [This](https://www.maketecheasier.com/sd-card-vs-ssd/) is an awesome article that explains the differences. It is 2017 but nothing has changed. – Señor CMasMas Aug 13 '20 at 16:37
  • Small microSD cards — and even USB flash drives that have large capacity but the bulk of their physical presence is the case itself — are not built to last. They technically work, but they have no resiliency, are not built to fail or even operate consistently under varying conditions. In contrast SSD disks of all kinds are just far more stable and resilient and also contain better memory management firmware. The way to look at it is a 16 ounce paper cup has the same capacity as a 16 ounce ceramic mug. You can reuse that 16 ounce paper cup but only a few times. The ceramic mug is built to last. – Giacomo1968 Aug 13 '20 at 16:54
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    @Giacomo1968 Fun comparison using cup and mug! – igorjrr Aug 13 '20 at 17:42

1 Answers1

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The difference is speed.

NAND-based SSD's and flash USB drives use similar but differing technology. "One of the major differences between a modern SSD using NAND flash and a micro-SSD card that also uses NAND flash is in the way the flash is accessed. SSDs have high-speed controllers designed to read and write data... to multiple flash chips at the same time."

Now Non-Volatile Memory Express (NVMe) is yet another implementation of NAND technology that is becoming more common, with increased parallelism, enabling yet faster I/O.

There are two issues with high-speed parallel operation that cause these devices to be made larger:

  • More interconnects are needed to support simultaneous parallel operations, so more space is consumed by "wiring".
  • More heat is generated, because more operations are being performed per second, so more area is needed to remove that heat.

To accommodate these needs, currently, SSD's are in larger enclosures. As progress is made with existing devices, or as new technology is introduced (memristors? 3-D IC's? Black swans??), surely circuits will shrink, and be less power-hungry.

DrMoishe Pippik
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