Mac OS X 10.5: Creating and maintaining a bootable "universal" external disk

You can make a "universally bootable" external hard disk that will work with both Mac OS X 10.5-compatible PowerPC-based Macs and Intel-based Macs.

This article has been archived and is no longer updated by Apple.

Creating the external bootable disk

Note: To initially set up the external disk, use a PowerPC-based Mac. These instructions are intended for an external disk that will be used with both PowerPC- and Intel-based Macs. If you're not sure what processor types your Macs have, see this article.

  1. On a Mac OS X 10.5-compatible PowerPC-based Mac, make sure the external hard disk has a Partition Map Scheme of "Apple Partition Map (APM)".

    This can be verified in Disk Utility. APM is the default Partition Map Scheme of PowerPC-based Macs.  In Disk Utility, select the external Hard Disk on the left side of the window and click Info.

    If the Partition Map Scheme is not APM, you will need to reformat the disk with Disk Utility with a Partition Map Scheme of "Apple Partition Map (APM)".  Important: Partitioning the disk will erase all data on it; back up important files that are on the external disk first.
  2. With the external hard disk connected to your Mac OS X 10.5-compatible PowerPC Mac, insert your Mac OS X 10.5 installation DVD and double-click Install Mac OS X.
  3. Go through the Mac OS X 10.5 Installer but select the external hard disk as the destination with whatever installation options that you want.

Once installation is complete, you will have an external hard disk that can start up ("boot") both PowerPC-based Macs (that are Mac OS X 10.5-compatible) and Intel-based Macs that were available when Mac OS X Leopard 10.5 was released.

Keeping Mac OS X 10.5 up-to-date for Intel-based Macs

Keep Mac OS X 10.5 on the external hard disk up-to-date so that it can start up future Intel-based Macs which may be released after your Mac OS X 10.5 Installer DVD was produced.

Simply connect the external disk to a compatible Intel-based Mac, select the disk in Startup Disk preferences, and restart. Once booted from the disk, choose Software Update from the Apple menu. Download and install any available updates.

Note: Support for the very latest shipping Intel-based Macs may not immediately become available via Software Update, but may be picked up in the next Mac OS X 10.5.x update. Your external disk may not be able to start an Intel-based Mac that shipped with a version of Mac OS X later than what is on the external disk.

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