I was using time machine to back up my G5 mac . I have switched to a mac pro now it won't back up to my external . Do I need to wipe my external from the g 5 backups to get it to back up again thanks David
Time machine requires a disk with a GUID partition scheme on an Intel Mac and a disk with an Apple Partition Map on a Power PC based Mac.
You need to use Disk Utility to change the partition scheme. Not sure if you can do that without wiping all the data.