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Windows MBR installed over Apple MBR  


I got a driver for recovery that was originally an Apple drive, but was hooked up to a Windows machine. The client inadvertently told the Windows machine to write a new MBR to it and it looks like it has been formatted. I'm a little stumped as to how to 1) get the data back, and 2) get the drive back into working order.

Posted : 06/04/2012 11:24 pm
Active Member

Apple uses GPT to format disks. All start with a protective MBR which has a record of OS type 0xEE. LBA 0 is the location for this protective MBR. When OSX or any other GPT compatible OS reads the drive, it checks if LBA 0 has a protective MBR. If MBR not OS type 0xEE or has more than one partition entry, it stops there. If protective MBR is OK, OS goes to check for LBA 1 and the last LBA on the disk.

LBA1 and the last LBA are GPT headers, the last LBA is a backup copy of the GPT header located at LBA1. So, you basically have to restore protective MBR and see if it helps. Then you have a backup GPT header followed by backup GPT partition entires at the back of the drive. Recreate the protective MBR to have its 64-byte area to contain a single 0xEE type Primary partition entry defined over the entire size of the disk and go from there. I think I saw some tools on the net (gdisk or similar) that can fix it automatically if you are not comfortable with a hexeditor. I would make a bit by bit copy of the drive before playing with the disk though.

Posted : 29/04/2012 5:09 pm
Senior Member

Work '1' first Get the data first BEFORE you try and get the drive back to working order. If nothing else, as ecophobia says, make a disk image.

If it is just the MBR, then any decent data recovery program should cope and will find the relevant start of the Mac partition - often at sector 0x64028. Some Mac disks do start with a FAT partition first though

Posted : 29/04/2012 9:02 pm