7 Replies Latest reply: Jan 2, 2008 1:07 AM by Wan Chai Man
Wan Chai Man Level 2 (395 points)
I have two (and a half) questions:

I have an WD 250GB IDE Hard Disk I want to use for Time Machine.

1. Does it matter if I choose GUID or Apple Partition Map for an IDE drive?

2. If I don't intend to use this drive as a start up disc can I just use Apple Partition map anyway?

2.5 Whats the advantage of GUID anyway?

iMac 2.0, iBook G4, Mini G4, Mac OS X (10.5.1)
  • Mr.Lobotomy Level 4 (1,290 points)
    1. My understanding is that Time Machine will not recognize a drive that is not GUID. Period.

    2. Extrapolating from http://en.wikipedia.org/wiki/Applepartitionmap and some experiences of other users who were having trouble with Boot Camp because their drives were not formatted GUID, it sounds like if you wanted your external disk to be bootable for both your Intel iMac and your PPC iBook and mini, then you would want the Apple Partition Map. I won't claim that my extrapolation is accurate, but it's derived from the idea that an intel mac can boot from an APM partition, but I don't know if the PPC will boot from GUID. So because you don't intend to use the drive as a startup disk, you can use GUID anyway.

    2.5 See http://en.wikipedia.org/wiki/GUIDPartitionTable GUID is for Intel machines and is an improvement over MBR (Master Boot Record).
  • Kappy Level 10 (263,335 points)
    As long as you do not plan to use it to install a fresh version of OS X then it doesn't make a real difference. Intel Macs can boot from both APM and GUID partitioned drives. You just cannot install an Intel version of OS X on an APM partitioned drive.

    GUID provides for on the fly altering of existing partitions non-destructively. It also permits the creation of both HFS and MSDOS partitions on the same drive.
  • howwow Level 4 (3,500 points)
    Well, I would recommend go GUID if you are using an Intel Mac, and using the drives for Time Machine backup.

    But *Mr. Lobotomy*, here's an interesting thing you might want to know - when I first connect my Maxtor One Touch 1TB FW 800 drive to my iMac for Time Machine backup, I formatted it as a normal Journaled disk (that was before I read about the GUID partitioning), the back up actually went well. i.e. Time Machine "sees" the drive and performed the back up as usual.

    But after I read about GUID, I just reformat/repartition it and re-run Time Machine again, so far so good.

  • imac007 Level 3 (845 points)
    And the answer is use GUID for Intel macs and use APM for PPC computers.
    Use Mac OS X extended journalled.
    The other thing you should know is about the proper computer name.
    Mac OS X 10.5: Time Machine backups are not visible
  • Wan Chai Man Level 2 (395 points)
    Thanks for your help guys!

    I have a mixture of Intel and PPC Macs & don't intend to use this for booting OSX and so I chose to use Apple Partition Map.
  • imac007 Level 3 (845 points)
    "Use "Apple Partition Map" partition scheme if the disk will be used with Time Machine and a PowerPC-based Mac.
    Use "GUID" partition scheme if the disk will be used with Time Machine and a Intel-based Mac."

    quoted from the Apple support site.

    APM does not work for both so you need to partition if the drive is big enough or get another drive.
  • Wan Chai Man Level 2 (395 points)
    I originally just plugged in my old backup disk that was formatted for APM & everything worked fine with my intel mac.

    Then I read that you are supposed to use GUID with an intel mac...so I reformatted it to GUID.

    After this but I had problems with Time Machine stopping during the first backup i.e. *WITH* GUID so..

    I finally formatted the disk as Apple Partition Map - even though its attached to an Intel Mac and everything works wonderfully again.

    Seems very temperamental!

    Thanks for all your help though:) I will buy a new disk later on in the spring.