2 different iMacs, which OS should I format my Passport?

Hi newbie here. I have a new 1TB Passport USB 3. I would like to use it to back up two computers;

  1. iMac  3.06 Ghz Intel Core 2 Duo OS 10.6.6 with an ancient WD 250 GB external Model WD2500B011

  2. iMac 800 Mhz PowerPC G4 768 Mb, OS 10.4.11


The instruction sheet stated the Passport is pre-formatted for Windows and to to go to support.wdc.com and download instructions how to reformat the Passport for Mac, but there are several choices for OS 10.4 and 10.6, which should I use?

Is there a way for me to also back up the older WD 250 GB external as well?

Many Thanks!


Hi there… If I were you, I’d format it GUID HFS+ for 10.6, since the APM HFS+ for 10.4 can be a pain on newer Macs… But GUID may not work properly for the older Mac since they do not have the same way to process the data…