06-16-2017 11:43 AM
06-16-2017 11:51 AM - edited 06-16-2017 11:52 AM
Sounds like it's running at sata 1. You would need sata 3 to get 500MB/sec. Based on your computers age, odds are it is sata 2 and should be capable of 260MB/sec.
However, do you know what motherboard chipset the computer uses? Some old Macs use an Nvidia motherboard whose chipset is flawed and can't correctly negotiate sata 2 when faced with a sata 3 drive. Such a system will then revert to sata 1 unfortunately.