I have a 500 GB Toshiba USB external hard drive, and what I want to do is have it formatted in a way that all of my machines can both read and write to it. The machines are as follows: 1. Early 2011 MacBook Pro running 10.11.6 2. eMac running 10.4.11 3. PowerBook G4 running 10.5.8 4. HP EliteBook running Windows 7 64-bit Is there such a format, or am I plain out of luck?