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Posted by Damien Biddulph on Tue 10th Jul 2012

Recently, I had to reinstall OS X from scratch. I was trying to install windows 7, and boot camp would not give me more than 5GB due to “unmovable files”. Anyway, after many attempts around this (google doesn’t have much in terms of solutions that work), I decided to do what most people say: Do what Apple / Boot Camp is asking you to do… reinstall the OS. So, that’s what I’m doing…

I boot off the snow leopard DVD, start up Disk Utility, and repartition my drive to one large partition (as strongly recommended when using GPT), and try to start the installation. The install button is grayed out! The message right above it states: “Mac OS X cannot startup from this disk”. Some google searches suggested this is because the MBR is somehow messed up (or the installer thinks it is). Several suggestions later (like, resize the partition so something smaller, then save, and immediately resize back to full) don’t seem to work (still getting the same error). So, I figured, since the MBR was messed up, maybe changing the partition type would wipe it out completely. For me, the solution was just that! I changed the partition to MBR via the Options button on the Partition tab. Of course OS X won’t install on MBR, if you don’t believe me try going back to the install screen after creating the new partition. Once the partition is saved, try the installer again (you will see a message that OS X can’t be installed on an MBR partition and it must be repartitioned as GPT in Disk Utility). So, then, change it back to GPT and Apply! Note: Once you create an MBR partition, everything will be grayed out (even the – (minus) and + (plus) buttons.) Don’t panic, just select 1 Partition from the pre-configured configurations pull-down (right above the partition display). Then, go into Options, select GPT, OK, and apply. Now, when you go to the install screen, it won’t complain.

Have fun installing OS X!

Source: mac os x cannot startup from this disk



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