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I've ordered micro SD cards multiple times from china, I always check them with H2testw to make sure they are real. However I've noticed something strange about the micro SD XC cards (only beyond 64GB), they have an empty unpartitioned space which is few megabytes, so for example in case of a 256GB micro SD card there are a 32MB empty unpartitioned space and a 235GB partition. If I delete the partition and re-partition the card in Disk Manager this 32MB unpartitioned space disappears and I would assume that the capacity of the new partition would be 32MB larger but no, if I repartition the card, the total size of the card becomes smaller than the original main partition, unfortunately I haven't checked how much, but its capacity will be smaller by a few megabytes or kilobytes, so it's not significant. So my questions are:

Why there is a small empty unpartitioned space on my brand new micro SD card?

Why the capacity of the card shrinks if I repartition the card?

Screenshot

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  • Can you describe in more detail how you figured out that "the capacity shrinks"? That is, exactly how did you repartition, and at which size did you look (the device size, the partition size, the filesystem size)?
    – u1686_grawity
    Sep 18, 2021 at 12:45
  • @user1686 I viewed the size in the windows file explorer / properties, there it shows byte accurate the size, as brand new it only shows the main partition's size and after repartitioning I think it shows the device's size since there is only one partition after I repartitioned it. I've repartitioned it in the windows disk manager.
    – Hatibovics
    Sep 18, 2021 at 17:33
  • @Ramhound "It should be smaller by no more than 32 MB." Shouldn't it be bigger by 32MB after I delete both partitions and create only one new?
    – Hatibovics
    Sep 18, 2021 at 17:36

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There are not two partitions. There is 32MB of empty space and a single partition taking up the rest of the space.

Typically space is left unallocated on drives in general cards due to partition alignment and SD cards and SSD in particular to allow the system to align partitions with erase blocks.

In the grand scheme of things having 32MB of unallocated space on a 256GB card is trivial, though Disk Management is showing it in a way that makes it look far more significant than it really is.

In real terms that "big" 32MB area should be a small fraction of a pixel wide compared to the size of the rest of the disk. It is shown large so that you can select and do meaningful things with it if you need to, which you don't really.

enter image description here

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  • "There are not two partitions." How stupid I am, yeah, it's really only one partition and an empty space. I know that disk management doesn't shows proportionally these areas, so I know that 32MB is absolutely not significant. However to align 512 byte blocks to 4 KB blocks 32MB seems too much space for that, but partition alignment would explain the size change after repatitioning. But why I haven't seen an empty space next to the partition before on brand new cards?
    – Hatibovics
    Sep 18, 2021 at 18:56
  • I've seen gaps like that on many memory sticks and many without as well. It's down to what the manufacturer bothered to set up in their tools, whether they thought it was necessary or if someone else formatted and changed it in between.
    – Mokubai ♦
    Sep 18, 2021 at 19:21
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    Wear-Leveling is another reason for the unallocated or unpartitioned space. Some SD cards use wear-leveling algorithms to spread out the writes and erases across the entire card, which can help prolong the life of the card by allowing the controller to move data around more easily. Some SD cards also use error correction codes (ECC) to detect and correct errors that occur during the read or write operations. It can provide extra space for the controller to store ECC information and improve the reliability of the card.
    – goetz
    Mar 3, 2023 at 18:10

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