Оригинальный сообщение: mister790 ,
You'll also want to confirm that your external drive is formatted correctly using Disk Utlilty. To serve as the start up disk for an Intel Mac like your iMac, it needs to be formatted with the GUID option rather than the Apple Partition option (which is what you'd need to boot up a Power PC). And once you've cloned your internal drive to the external drive, you should definitely test to make sure the external drive will boot up your computer by restarting with the Option key held down. Select the external drive when you're given the option. If it boots up correctly and everything seems to be working, you should be good to go to swap the drives.