The Boot0 Issue:

Upon successful installation, boot from hard drive results in a boot0 error:


Loading Operating System …
 boot0: GPT
 boot0: test
 boot0: test
 boot0: GPT
 boot0: test
 boot0: test
 boot0: error

The Actual Problem:
Due to the storage size of large drive, manufacturers had to change the default block size from 512 bytes to 4,096 bytes. The large drives are known as “Advanced Format” or 4K drives. Initially this was only seen on drives larger than 1 TB, but this change will be standardized and on all drives to lower manufacturing costs.  Windows and Linux resolved their boot loaders quickly, but OSX was a little slow to catch-up because Apple didn’t ship systems with drives larger than 1TB until a couple of years ago.  As part of this change there is an issue with OS X writing the boot code to the MBR sector.  Thankfully, you can write to the MBR manually (Yay!) in order for the OS to boot.  So, yes – you can purchase and replace that old Apple 1TB drive with a nice shiny 2TB drive.

Be mindful – your mileage may vary.   If you’re not a geek or a genius – you should just accept Apple’s configuration and/or buy a new machine.


  1. Install Mountain Lion from a USB drive.  (if you don’t have one, google it)
  2. Boot new installation using the same USB drive.
  3. Run install scripts as normal – network, sound, etc.
  4. Reboot system back into Mountain Lion installer from the USB.
  5. At the second prompt (after welcome), run the Disk Utility and unmount the Mountain Lion drive you just installed.  The drive has to be “unmounted” and not in use when you write to the MBR.
  6. Launch Terminal from the utilities menu and execute the following command:


dd if=/usr/standalone/i386/boot1h of=/dev/disk0s2
  1. Exit Terminal
  2. Reboot Normally
  3. Laugh at the Sky
NOTE: The above instructions are based on OS X being installed to a hard drive connected to SATA port 0. If you are using a different port you will need to get the drive device name from Disk Utility by selecting the volume and clicking Info.  This post is intended as a personal note for my own use (had to do this on my box), but you may find it useful. You can find other guides on the internet that are similar if you don’t like this one.