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I have a macbook pro running Snow Leopard. I have Tuxera NTFS drivers.

I have a microSD card, in an adapter, in the slot. The "lock" slider is in the "unlocked" position.

'Get Info' tells me the drive is formatted to FAT16. The permissions panel tells me that I can only read.

Disk utility tells me it's not writable. (It does this for the volume and also for the higher level Apple SD Card Reader Media)

What do I need to do to change permissions to turn this card writable?

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format it as Fat32 –  Jason Dec 4 '12 at 23:47
@Jason - I can't format it. Disk Utility can't write to it, thus can't format it. –  DanBeale Dec 4 '12 at 23:59
Is it a microSD card sold as rewritable media? This is expected behavior for read-only cards that might only be used for specialized purposes. Corollary: can you write to the card from a Windows computer? NTFS drivers shouldn't be necessary -- FAT16 can be natively written to in Mac OS X. –  NReilingh Dec 5 '12 at 0:25
It is a card sold as re-writeable media. It has, previously, been written on. FAT16 can be natively written to by OS X - but nothing is allowing me to write anything to this card, even though it is currently FAT16. –  DanBeale Dec 10 '12 at 13:32

2 Answers 2

up vote 2 down vote accepted

I've encountered the same. Ended up doing this:

  1. Backup the SD Contents
  2. Format the SD as FAT16 using Disk Utility and Terminal

following these steps:

  1. Unmount (not eject) the SD from Disk Utility and copy the id (doing CMD+I on the SD and then selecting the Disk Identifier value (e.g. disk2s1))
  2. Format to FAT16: sudo newfs_msdos -F 16 /DEV_PATH/TO_SDK so in my case: sudo newfs_msdos -F 16 /dev/disk2s1


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I had a PNY 32gb SD Card. Spent hours trying to find out how to make it re-writeable. Well the answer is simple. The slider on the left side of the card must be "up" (the read-writable position) BUT ALSO the tiny "notch" opposite the slider must be covered with a piece of tape. It's really the opposite of the old video tapes, which we had to break the tab if we did not want anything recorded over it. But I can guarantee you I've bought a lot of SD cards and have NEVER had a card that was write-protected out of the package that required me to do anything but raise the slider on the left side.

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