Author Topic: Partition information on the MBR of an SDCard...  (Read 20551 times)


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Partition information on the MBR of an SDCard...
« on: December 16, 2011, 12:40:48 pm »
Was wondering if any here know the how's and why's of the partition table information on a SDCard.

Here's a problem I have been having:

1. I ask the tech to bulk erase a batch of SDCards. He does this on a SDCard programmer.  So it will be difficult to tell exactly what the programming is doing.  Let's assume the cards are totally wiped clean.

2. He formats the newly cleaned SDCards on a Windows7 box.  I assume Windows 7 defaults to FAT 16 for such media.  

3. That SDCard will now auto mount under Windows 7.  It will even auto mount on a Linux / Fedora 13 box!  Everything looks fine.

4. But that same SDCard will not mount on our embedded Linux target!!

I checked that SDCard with the fdisk utility on the Fedora 13 box.  What do you know!  The partition table entries appear to be completely random.  They make no sense!  

A similar fdisk utility on our embedded Linux target concurs with these findings.

Here's where it gets even better (I think).  Using either our Linux target or the Fedora 13 fdisk utility I can delete these (seemingly) randomly created partitions from the SDCard's partition table and  write back out a table describing 1 FAT 16 partition.  Now, if I format that newly partitioned SDCard in the same Windows 7 box...  I can mount that card on our embedded Linux target. What's up with that?  ???

What am I not understanding about partition tables?

How can the SDCard driver on Windows 7 and on Fedora 13 mount an SDCard that fdisk thinks is full of random partition information?

Am I using an old / obsolete fdisk?  Did the rest of the world move on to something other then fdisk and not tell me?  (How could they do that to me!)

-thanks for any help.

« Last Edit: December 16, 2011, 12:42:44 pm by st2000 »

Jan Axelson

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Re: Partition information on the MBR of an SDCard...
« Reply #1 on: December 19, 2011, 11:08:42 pm »
I don't know if this is what you're seeing, but some mass-storage devices with single volumes don't have a master book record (MBR) sector or partition table. And some hosts may have trouble accessing these devices.