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Old Apr 12, 2009, 02:23 PM   #1
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Join Date: Apr 2009
Delete EFI system partition. Convert GPT back to MBR

Hello All,

I need some help to convert a GPT (GUID Volumes) hard drive back to an MBR format so I can again use it with windows.

I converted a 500G External USB SATA hard drive from MBR to GPT no problem. It could be done using either Vista 32bit or WinXP 64bit the conversion under XP Pro SP3 32bit was not possible maybe because diskpart was still an older version and not updated to a newer version.

My work on the Mac is done now and I want to convert my drive back to MBR so I can use it with windows. I've erased and then deleted all the partitions I had created on the drive. Using WinXP 32bit and Disk Management I see only one big partition (465.76 GB Healthy (GPT Protective Partition))
Using WinXP 64bit and Disk Management I can see there is a 200Mb EFI Systems Partition followed by 464.44 Gb of Unallocated space.
How do I get rid of this EFI Systems Partition that is stopping me when using diskpart to convert to MBR?

My sister bought a second hand Mac Book Pro. According to Mac Book Pro specs. this unit should have had a 250G - 320G Hard Drive but someone had replaced with a 120G before she got her hands on it. My assumption then is that they\whoever it was that switched the drive must have also replaced the DVD drive at the same time as well.

The DVD drive that this second hand Mac Book Pro came with cannot fully install from a Dual Layer DVD. It crashes half way through.
I did a bit of searching and found that other people were also posting remarks about this same drive with the same firmware revision on it. Which leads me to believe that even though the firmware states the drive is compatible with DL discs, in actual fact it is not.

I was able to find a friend that somehow converted the install DVD into a .dmg image file that I could use as my install media off a 8G USB external (flash) drive.

I copied this .dmg file onto the ext. SATA hd. I used Disk Utilty and created 4 partitons 1 - 30G to do a trial test installation of the Mac OSX too; a 2nd small 8G partition I could restore the install media too; and 2 other larger partition 1 - 120G to clone her original internal drive too with a previous version of Mac OS X installed on (used SuperDuper to do the clonning) and the last drive was for any other install programs that she needed reinstalling after the Installation of OS X to the internal drive was complete.

With Disk Utility running, I then went to 'Image' on the file menu and choose 'Scan image for Restore' (the .dmg file). The image was then comfirmed to be good and could be used to restore or install Mac OS X.
I restored the image onto this 8G partiion when finished I had Mac OS X Install DVD now on that drive. When I rebooted (holding down the Options key) I and was able to boot and install OSX 10.5.6... First as a test I installed it to the ext. hd on the 30G Extended (journaled) partition I previously created and everthing went smoothly. So I installed it to her internal hd.

Now my work is done. This is an External SATA Hard Drive connected through the USB port. Not an internal hd.

I don't have a DVD Drive capable of reading the Dual Layer DVD.
I've read somewhere that I could try booting from the OS X install DVD and use Disk Utility before the setup process and choose to make the drive Generic instead of GUID? But chances are this is only going to reflect on the internal drive. Then external drive might not even exist in the options.

I don't have a usable DVD because it is a Dual-Layer DVD that my drive will not work with.

I have the Mac OS X Install DVD as an image Only on an 8G OCZ2 USB flash drive now. I tested the install of OSX with it and all was good. I then cleaned the Mac stuff off the external USB connected SATA drive as best I could.

When I run the install of OSX off the flash drive, I don't see any options as to where I can select to run Disk Utility. I come to a page where it asks me where to install it too. I'm afraid that if I choose the external drive, it will just start installing the OS because there is still an EFI systems partition on the hard drive. If it does install it again then I will have to erase it again and still be no closer to getting this drive back to an MBR format.

Any help in this matter would be greatly appreciated.

Last edited by leogets; Apr 12, 2009 at 02:31 PM.
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Old Apr 12, 2009, 02:46 PM   #2
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Join Date: Jun 2007
You should look in the menu bar up top for disk utility. I forgot which menu its under but just explore and if you want to have the drive partition table as GUID.

As for your external drive, to get from GUID back to MBR go to disk utility in os x and select the drive (not the partition)... then go to the partition tab and under teh volume scheme menu select "1 partition". After that click on the "options..." button at the bottom and choose master boot record.
I own everything

Last edited by milk242; Apr 12, 2009 at 02:52 PM.
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Old Apr 12, 2009, 05:56 PM   #3
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Thanks milk242 for your reply and it worked perfectly....

Thanks again.
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