Installing Leopard to an external firewire drive

Earlier, we published a tutorial explaining how to clone the Tiger installer DVD to an external FireWire drive. In that tutorial, we suggested that while you're doing this you should also have a second partition on the external drive on which you can actually install the system. Well, now the truth can be told; in that tutorial, we were just preparing you for a valuable Leopard installation technique.

You see, Leopard is the first Mac OS X system that comes on a Universal Binary DVD. The very same DVD can be used to install Leopard either on a PowerPC Mac or on an Intel Mac. This means that the very same system can be used to start up either a PowerPC Mac or an Intel Mac. With Leopard, you can make a universal boot disk.

Since Leopard is very new, and since not every application has been updated to work with it, an external firewire boot disk can be a very good way to get started. Think of the advantages:

• You don't have to repartition or change anything on your computer's internal hard drive.

• You can switch back to Tiger instantly at any time.

• The very same firewire disk can be used to boot different computers into Leopard (though not, of course, simultaneously).

This, in fact, is how we worked with Leopard seeds all during the (very long) beta testing period leading up to Leopard's release. And it worked great! There is a disadvantage to this approach: if you have a portable computer, then Leopard will not be part of that portability (unless you want to carry the external firewire drive around with you along with the computer). But this, we found, was a small price to pay, since even a portable computer is used sitting in just one place most of the time.

The secret behind the universality of the Leopard boot disk is that, although a PowerPC Mac will not boot from a GUID-partitioned disk (the "native" partitioning for an Intel Mac boot disk), an Intel Mac will boot from an APM-partitioned disk (the "native" partitioning for a PPC boot disk). So, the trick is: if you have both a PPC machine and an Intel machine that you'd like to be able to boot with a Leopard external firewire disk, use the PPC machine to perform this procedure. (If you don't have a PPC machine, then just use the Intel machine; your Leopard external firewire disk won't be able to boot a PPC machine, but you won't care.)

Okay, to sum up the procedure, here's what we suggest:

• Get yourself a nice big external firewire hard drive. You're going to want one to use with Leopard anyway, so you can use Time Machine. (Time Machine will probably not back up to a partition on an internal drive; it's looking for an external drive.)

• Use Disk Utility (you can do this with Tiger) to repartition the drive. As you do the repartitioning, take great care to specify the correct partition scheme! If you're using a PPC machine, you want the Apple Partition Map (the default). If you're using an Intel machine (because you have no PPC machines), you want the GUID partition scheme; it is easy to neglect this step, and if you do, and you accidentally use APM, you won't be able to make a Leopard bootable disk. We suggest three partitions:

  • A 10 GB partition to hold the clone of the Leopard DVD.
  • A 30 GB partition to hold the Leopard system.
  • All the rest to hold Time Machine backups.

• As described in the earlier tutorial, insert your Leopard installer DVD into the computer and make an image file from it. Now "restore" (clone) the image file to the first partition on the external firewire drive.

• The first partition on the external firewire drive is now bootable: it is a clone of the installer DVD. So boot from it! The effect is just as if you had booted from the installer DVD: the installer will offer to install Leopard. Do an erase-and-install onto the second partition of the external firewire drive.

At the end of the installation process, the installer will automatically reboot the computer from the Leopard system it just installed on the second partition of the external drive. You will have to go through the usual kerfuffle about creating an initial admin user, declining the opportunity to subscribe to .Mac, etc. When you're all done, you'll be running Leopard from an external drive.

You should probably immediately use the Spotlight and Time Machine system preferences to set things up correctly. Your goal here is to prevent the computer from bogging down (and the fans from spinning up) by immediately indexing and backing up a bunch of unnecessary stuff.

You now have an external firewire drive that can boot your computer into Leopard. Remember to "put away" this drive properly before turning it off or unhooking it from the computer! To revert to Tiger, for example, you would use System Preferences to select the computer's internal drive as your startup drive, then restart the computer (booting into Tiger), and then, when the Finder has come up and you can see the external drive, you can "eject" the external drive. Then, and only then, you may disconnect it or shut it down.

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