[Yokohama]

I've migrated apps and files from my old G5 iMac to a new Intel iMac. The external HD I've been using with Time Machine to back up the old iMac's files is full and TM and the G5 iMac had been going back and erasing the earliest backups in order to back up the latest files. Now I want to carry on doing this with my new Mac but can't: the message from TM says the disk is almost full, so I should use a new HD. (The new iMac had he same name as the old iMac, so I've given my new iMac the same name as the ext. HD, as someone suggested. But I can't back up with either name, though at least now I get a message from TM saying the HD is full.) Is there any way to get TM to erase the earliest back-up files and using that space to back up my new work on the new iMac? Or do I really have to erase everything on the ext. HD and start backing up fresh?

[Yokohama]

I got through to Apple Support about my TM problem. The answer is I had to erase my data back-ups on the ext. HD and start afresh in order to use TM on my new iMac with this HD. If I understood correctly, each Mac uses a different ethernet number and therefore TM on the HD couldn't recognise my new iMac's number. Something you might want to consider when buying a new Mac!