Disable internal hard drive
IMAC 2 GHz PowerPC G5, Mac OS X (10.4.7)
Not without opening the computer and physically disconnecting the SATA cable. If you are going to open it, then it would be equally as simple to just replace the HD with a SSD. That would bring new life into the machine for as long as it continues to function. You an find how to instructions by clicking here
Disable internal hard drive