SATA-cable recognizes HDD but not SSD
I have read where the logic board is capable of working with SATA III drives which allows for the installation of either a HDD or SSD. When a Mac is sold with a HDD, usually this is a SATA II drive. Therefore, the cable used is designed for this type of drive. The cable can not be used with SATA III drives. When sold with a SSD, this is a SATA III drive. In this case, the cable used is designed for a either a SATA II or SATA III drive. 


  The end result is that if you started with a HDD, then a upgrading to a SSD may require a different cable.