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If your G4 has a Firewire port then you can connect it to your new Mac with a Firewire cable - 6 pin to 9 pin cable. You will need a Thunderbolt to Firewire adaptor for the new computer. You would useTarget Disk Mode by booting the G4 into TDM and the new computer normally. If it works then the drive in the G4 will appear on the new computer's Desktop.
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