Ask Different is a question and answer site for power users of Apple hardware and software. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I just finished the huge download of Mac OS X Lion, started the installer, and now I have a problem. The installer says that I must have the GUID-Partitions Table Scheme.

The problem is that when I go into the disk utility, I can't change the format anymore, because I have Master Boot Record as type.

Can anyone help me, please?

share|improve this question
Which OS are you upgrading from? – Philip Regan Jul 20 '11 at 17:48
I have heard of tools to change things on the fly but can't recommend them. Do you have a spare HD to hold the contents of the drive while it is erased and changed to the correct format? It's normally quite a trick to get Snow Leopard installed on MBR drives. Well done! – bmike Jul 20 '11 at 17:53
Can one upgrade from anything other than Snow Leopard? – lkraav Jul 20 '11 at 17:56
@lkraav: No. Upgrading to Lion requires Snow Leopard. That is why I asked my question in the comments. – Philip Regan Jul 21 '11 at 0:19
up vote 3 down vote accepted

Ok thanks for your help, but I solved the problem on my way, here's what I've done:

  1. Backup everything important to an external Harddrive
  2. Inserted the Mac Installation Disc and ruined there the disc utility app.
  3. I removed everything from my HD and it was GUID-Partioned.
  4. Now I just installed Mac Os X 10.6.2 and updated to 10.6.8
  5. Now I could run the installer of Mac Os X Lion without any problems and as a benefit of the whole thing, I started with a brand new Mac Os X Installation, without any trash in the file system.
share|improve this answer

search: claims that is able to do MBR -> GPT conversion.

Then there's supposedly some not-for-faint-of-heart options mentioned in that thread, which IMHO judging from the tone of the original question, are not safe enough to use. At least make a whole disk backup first.

share|improve this answer
I have used iPartition a few times to change partition schemes without destroying data partitions. – Graham Perrin Mar 30 '13 at 15:20

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.