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For Android devices, is internal storage memory typically faster, slower, or equal to microSD card storage?

For example, let's take the Samsung Galaxy S10 Android phone. It comes in 128GB, 512GB, and 1TB storage configurations. It also has a single microSD card slot.

The cost difference between the different tiers of integrated storage is slightly more than cost of a comparable microSD card, but not a big difference.

Which will result in better performance: An Android device with only integrated storage, or one with an equivalent amount of storage in the form of integrated storage + a quality microSD card?

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The internal flash is usually way faster than an SD-card. In your example, the Samsung Galaxy S10 uses UFS 2.1 storage for interfacing with the internal flash chip.

UFS 2.1 for the 1TB storage configuration you can expect in reality about (maximum values):

  • 1000 MB/sec sequential write speed
  • 260 MB/sec sequential write speed
  • 50000-58000 IOPS

If you try to get a micro SD-card, there are a few that are as fast as the internal storage, but they use the UHS-II standard or newer (max ~620 MB/sec). For UHS-II, the micro SD-card reader in the phone needs additional contact points, but only recent high-end phones have such a reader integrated (I have read that the Samsung Note 10 released 2019 was the first Samsung phone to have such a reader).

Another problem of micro SD-cards is their size. The faster cards require a lot of CPU speed of the CPU integrated in the card. Because of the small size the card is very limited regarding dispensing the created heat. If you for example use such a micro SD-card in a PC card reader the micro SD card is getting hot very fast and then starts throttling the read/write speed.

But development of UFS also does not stop. Just recently, UFS 4.0 has been announced which can reach transfer speeds that are common for NMVe SSDs in a PC (up to 5GB/sec).

Therefore, for most micro SD cards, I would expect that speed of a combined set-up of integrated storage + a quality microSD will not be faster that the internal flash chip alone. Because of the latency of the micro SD-card, it might be even slower (but that may depend on the used phone and the micro SD-card).

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  • Very helpful answer Robert. Thank you! If you will, please confirm that the edit I made to the first sentence is correct.
    – Amazon Dies In Darkness
    Commented May 11, 2022 at 16:18
  • Question regarding your answer: You mentioned a CPU in the 3rd paragraph from the end. Are you referring to a CPU on the microSD card?
    – Amazon Dies In Darkness
    Commented May 11, 2022 at 16:19
  • Based on your helpful answer, would a UFS 2.1 device with all internal storage be the fastest, followed by one with large capacity internal storage + small capacity microSD, followed by one with small capacity internal storage + large capacity microSD? To keep the comparison easy, let's assume the total storage capacity (internal + microSD) will always be 512GB.
    – Amazon Dies In Darkness
    Commented May 11, 2022 at 16:22
  • @RockPaperLz-MaskitorCasket UFS is the standard for the integrated flash chip not the SD card, I have corrected that. THE CPU is indeed the CPU of the microSD card. Often this is also an ARM processor but a much smaller one.
    – Robert
    Commented May 11, 2022 at 16:41
  • @RockPaperLz-MaskitorCasket And for the combinations: a larger internal storage should be faster. As internal and micro SD-card are not building something like a RAID where both storage systems are used at the same time for each request, instead it should be more like JBOD, some requests are processed by internal and some by external but never both (not sure how Android distributes them). Hence speed can be as fast as internal storage but I would expect them not to be faster. And how much slower depends on the used micro SD card (the capacity is not really important).
    – Robert
    Commented May 11, 2022 at 16:44

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