MacOSX ate my pics
August 6th 2008

OK, so the 2GB SD card I use in my camera has its problems. Apparently, only 1GB of it are recognized by the OS (Linux) and/or the card readers I own. The problem seems to be common, as you can see by googling about it. More info, from the Wikipedia article for SD cards:

Devices that use SD cards identify the card by requesting a 128-bit identification string from the card. For standard-capacity SD cards, 12 of the bits are used to identify the number of memory clusters (ranging from 1 to 4096) and 3 of the bits are used to identify the number of blocks per cluster (which decode to 4, 8, 16, 32, 64, 128, 256 or 512 blocks per cluster).

In older 1.x implementations the standard capacity block was exactly 512 bytes. This gives 4096 x 512 x 512 = 1 gigabyte of storage memory. A later revision of the 1.x standard allowed a 4-bit field to indicate 1024 or 2048 bytes per block instead, yielding more than 1 gigabyte of memory storage. Devices designed before this change may incorrectly identify such cards. Usually by misidentify a card with lower capacity than is the case by assuming 512 bytes per block rather than 1024 or 2048.

For the new SDHC high capacity card (2.0) implementation, 22 bits of the identification string are used to indicate the memory size in increments of 512 KBytes. Currently 16 of the 22 bits are allowed to be used, giving a maximum size of 32 GB. All SDHC 4-GB and larger cards must be 2.0 implementations. Two bits that were previously reserved and fixed at 0 are now used for identifying the type of card, 0=standard, 1=HC, 2=reserved, 3=reserved. Non-HC devices are not programmed to read this code and therefore cannot correctly read the identification of the card.

All SDHC readers work with standard SD cards.[ref]

Many older devices will not accept the 2 or 4 GB size even though it is in the revised standard. The following statement is from the SD association specification:

"To make 2 GByte card, the Maximum Block Length (READ_BL_LEN=WRITE_BL_LEN) shall be set to 1024 bytes. However, the Block Length, set by CMD16, shall be up to 512 bytes to keep consistency with 512 bytes Maximum Block Length cards (Less than and equal 2 Gbyte cards[ref]."

I have had problems in the past with this issue, and could only retrieve the photos exceeding the "first GB" of the card with a tedious operation: copy some photos from the card to the internal memory of the camera (28MB), remove the card from camera, connect camera to computer, download the photos in the internal memory (and empty it), unplug and repeat. 1GB/28MB = boring as hell.

However yesterday I realized that I had a shinny MacBook with its MacOSX intact. I read somewhere that Windows would sometimes read 2GB cards that Linux couldn't, by the simple method of happily ignoring the f*cked up file system in them. Maybe MacOSX could, too.

Well, it turns out it couldn't. When I attached the card in the card reader (I didn't try with the camera directly), MacOSX found the device and mounted it, giving me a nice icon in the Mac version of "My PC". However, the directory the icon led to was empty. I thought "Tough luck, Mac reads nothing in the card", unmounted it and unplug it. Then I placed it in the camera again, turned it on and... there was no photo in the darned thing! MacOSX had erased them!

There is still the (likely) possibility that I made some deep mistake, but the explanation for now seems that MacOSX ate my pics. Sad.

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One Response to “MacOSX ate my pics”

  1. 2 GB SD cards properly read under Linux | handyfloss on 02 Jan 2009 at 13:03 pm #

    [...] how MacOS X ate my pics? In that post I explained that Linux had problems with >1 GB Secure Digital [...]

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