The SATA standard specifies a power connector sharply differing from those used by PATA drives and many other computer components. It is wafer-based, 15-pin shape. The seemingly large number of pins are used to supply three different voltages — 3.3 V, 5 V, and 12 V.

Each voltage is supplied by three pins ganged together (and 5 pins for ground). This is because the small pins cannot supply sufficient current for some devices. One pin from each of the three voltages is also used for hotplugging. The same physical connections are used on 3.5-inch and 2.5-inch notebook  hard disks.

The SATA 15 pin power supply connector is one of the standard peripheral power connectors in computers today.

This power connector is the standard connector for all SATA based hard drives and optical drives.

Below is the pinout for the standard SATA 15 pin peripheral power connector as of Version 2.2 of the ATX Specification (PDF).

Note: There also exists two less common SATA power connectors: a 6 pin connector called a slimline connector (supplies +5 VDC) and also a 9 pin connector called a micro connector (supplies +3.3 VDC and +5 VDC). The pinout tables for those connectors differ from the one below.

Note: If you're using this pinout table to test power supply voltages, be aware that the voltages must be within ATX specified tolerances.

You can see other ATX power supply connector pinouts in my ATX Power Supply Pinout Tables list.