I have a Mac G4 with a 20 GB hard drive on the right side and a 300 GB hard drive on right side of desktop. I would like to make the 300 GB the primary driver but all the operating system is on the 20 GB and will not let me download or us the 300 GB. It shows that the 300 GB is an external drive but I don't know what that means. I just want to know if I can change the two drivers and make the larger driver the primary driver and how. The plugs are not the same so I just can switch the plugs. If anyone has any suggestion I would truly appreciate the help.