Install Snow Leopard from External Firewire or USB Hard Drive: How to Upgrade to Mac OS X 10.6 Without a DVD Drive
If you have a Mac without a functioning DVD drive (or a MacBook Air), you’ll need to find another way to upgrade to Snow Leopard, thankfully this is very easy, all you’ll need is an external firewire or USB hard drive. You’ll need access to a DVD drive *somewhere* so that you can make a disk image of the Snow Leopard install disk with the Disk Utility tool, but once you have the disc image you won’t need the DVD drive again. What you WILL need the entire time though is an external Firewire or USB drive that you don’t mind formatting, so that you can make the device bootable and upgrade to Snow Leopard from it.
As some readers pointed out, this step isn’t required. If you do need to, you can create a DMG file of the Snow Leopard disk, this is very easy.
* Launch Disk Utility
* Select the Snow Leopard DVD within Disk Utility
* Click the “New Image” button at the top
* Name the image and put it somewhere you can find it easily (Desktop)
* Click OK and wait for the image to be created
Easy enough right? Ok so here’s how you create a bootable Snow Leopard installation drive out of your external firewire or USB hard disk.
Install Mac OS X 10.6 Snow Leopard from an external Firewire or USB drive
* Launch Disk Utility
* Select the External Firewire/USB device that you want to use as the boot drive for the upgrade
* Click “Partition” from the menu options
* Select 1 Partition, then click “Options” below the partition scheme
* Select the top option for “GUID Partition Table” – it MUST be GUID to be bootable!
* Click OK to create the GUID partition (this will reformat the drive, ie: all data is lost)
* Next, click the “Restore” tab within Disk Utility
* Select your newly made Snow Leopard 10.6 Install DVD image and restore this image to the GUID partition you just created OR…
* Alternatively, you can select the Snow Leopard Install DVD and restore directly from the DVD to the GUID partition
* After the restoration is complete, your GUID partition will now be bootable by Mac OS X!
* Reboot the Mac holding down the “Option” key to pull up the boot loader, select the Snow Leopard install drive you just created rather than your default Mac OS hard drive
* Install Snow Leopard as usual!