Quote from a Western Digital FAQ (last copied March 22, 2011) and may need updating):
Mac computers can use WD external drives to boot into the Mac OS; however, not all WD drives can boot both Intel and PowerPC Mac computers. Below is a listing of drives that have been tested with a Mac. The tables separate drives based on their interface (USB/FireWire) and capability to boot Intel or PowerPC Mac computers.
Note: While it may be possible to boot your computer to an external hard drive,
Western Digital does not provide technical support for booting your computer using an external hard drive.
The following external hard drives should be bootable on Intel-based Mac computers systems through USB:
My Book Essential Edition
My Book Essential Edition 2.0
My Book Home Edition
My Book Mirror Edition
My Book Office Edition
My Book Premium Edition
My Book Premium Edition II
My Book Premium ES Edition
My Book Pro Edition
My Book Pro Edition II
My Book Studio Edition
My Book Studio Edition II
My Passport Studio
The following external hard drives should be bootable on Intel-based Mac computers systems through FireWire (1394a/b):
My Book Home Edition
My Book Mirror Edition
My Book Office Edition
My Book Premium Edition
My Book Premium Edition II
My Book Pro Edition
My Book Pro Edition II
My Book Studio Edition
My Book Studio Edition II
My Passport Studio
The following external hard drives should be bootable on Power PC based Mac computers systems through FireWire (1394a/b):
WD My Book Premium Edition
WD My Book Pro Edition
The following external hard drives should not be bootable on Power PC based Mac computers systems through USB/FireWire 1394(a/b):
All My Book (+SmartWare)
All My Passport (+SmartWare)
My Book Essential Edition
My Book Essential Edition 2.0
My Book Home Edition
My Book Mirror Edition
My Book Office Edition
My Book Premium Edition II
My Book Pro Edition II
My Book Studio Edition
My Book Studio Edition II
My Passport Studio
My Passport Elite
My Passport Essential
WD Passport
WD Passport (Silver)
The following external hard drives should not be bootable on Intel-based Mac computers systems through FireWire (1394a/b):
All My Book (+SmartWare)
All My Passport (+SmartWare)
The external hard drive must contain a Mac OS Extended (HFS+) partition with GUID for Intel-based computers or Apple Partition Map on PowerPC-based computers. For directions on how to partition and format an external hard drive, please follow the directions below:
. Ensure that the external hard drive is connected to the computer and powered on. Open the main drive (the drive that contains the operating system).
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. Open the Applications folder.
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. Open the Utilities folder.
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. Open the Disk Utility application.
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. The drives are displayed on the left side of the window. Click on the drive (the upper listing with the numerical capacity) that you wish to partition.
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. Once the drive is selected click on Partition tab.
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. Click on the Options button to select the partitioning scheme.
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. Click on GUID for Intel-based computers or Apple Partition Map for PowerPC-based ones and then click on the OK button.
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. You will see several options for setting up the drive. Once you have selected the number of partitions, the format type you want (Mac OS Extended), and a volume label, click the Apply button. Click the Partition button to confirm your selection and begin the partition operation.
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. Following the completion of this process, the drive will appear on the desktop. It is now ready for installing a bootable operating system on it.
Source:
http://wdc.custhelp.com/cgi-bin/wdc.cfg/php/enduser/stdadp.php?p_faqid=1787&p_created=1203707437&p_sid=dO9DFidk&p_accessibility=0&p_red irect=&p_srch=1&p_lva=&p_sp=cF9zcmNoPTEmcF9zb3J0X2J5PSZwX2dyaWRzb3J0PSZwX3Jvd19j bnQ9MjQ4LDI0OCZwX3Byb2RzPSZwX2NhdHM9JnBfcHY9JnBfY3Y9JnBfcGFnZT0xJnBfc2VhcmNoX3Rl eHQ9Ym9vdGFibGUgb24gbWFj&p_li=&ptopview=1
A few basic facts to consider when buying a hard drive:
http://macs.about.com/od/peripherals/bb/exthd.htm
