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SD-Cards Comparison

As you can see above, Some contacts seem to be longer than the rest. Also, on the SD card (2nd from top) the last one seems to be thinner and also closer to the seventh pin.

Why not just uniformly place all contacts of same sizes at uniform distances??

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  • 15
    Not an exact duplicate, but the reason is the same as in superuser.com/questions/1020234/…
    – André Borie
    Jan 1, 2016 at 18:26
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    @AndréBorie incidentally, that was the question which inspired me to ask this one... :)
    – undo
    Jan 2, 2016 at 6:23
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    @RahulBasu: Then you already know the answer...?
    – BlueRaja - Danny Pflughoeft
    Jan 2, 2016 at 8:36
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    @BlueRaja-DannyPflughoeft Actually, I wasn't sure if the answer was the same... Plus there were the 7th and 8th pins on the SD...
    – undo
    Jan 2, 2016 at 8:37
  • REPOSTED howtogeek.com/238195/…
    – undo
    Jan 9, 2016 at 12:03

1 Answer 1

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The power and ground pins stick out further, so that power is applied/removed before/after the data pins are connected/disconnected.

Pins 8 & 9 were added to the MMC format in making the full-size SD format. So there was not room for a full-sized 8 (maintaing backward compatibility), and perhaps they learned a thing or two about applying/removing power first between MMC and SD (or about making it cheaper without an extra switch if they extended the pins).

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    @RahulBasu You'll notice this design on a lot of new technology-- anything that's designed to be hot-swappable will have ground/power sticking out further. USB, SATA, PCI(e), and so on all typically have ground and power connected first so that the device will always have power before it has data, and will always have power while it has data (assuming the connection's not bad).
    – phyrfox
    Jan 1, 2016 at 21:02
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    MMC cards don't support hotplugging. Mobile phones and digital cameras that used MMC had a Reject option somewhere in the menu. Choosing it unmounted the card and disabled power so that you could swap the card safely.
    – gronostaj
    Jan 2, 2016 at 12:50

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