We don't have enough information. We need to know if it is an EIDE (PATA) or SATA drive. 4 pins on an EIDE drive could very well be for the power connection. 7 and 15 suggests SATA, however, and they don't use Master/Slave settings. Therefore, I suspect the 4 pins you are referring to are for Legacy support - to force the drives to use older SATA protocols on some older motherboards. Some SATA drives have two more pins in that location for standby power and some include yet another pair for spread spectrum clocking - two features most users don't ever need.