Why are there so many pins on a SATA power connector

computer-architectureconnectorpower supplysata

I was just looking at the power connector for a SATA optical drive and noticed that it had fifteen pins!

I then marveled at the data connector next to it, which has a measly seven pins.

I know that there are only physically three pins needed for the power connection:

  • +12v DC
  • +5v DC
  • Ground

Why did they decide to use a fifteen-pin power connector that's twice the width of the data connector?

Best Answer

Here's the SATA data & power pinouts.

Remember, SATA is a serial bus. This means data transfer only needs two paths -- TX (transmit) and RX (receive). In the case of SATA, there are actually two pins for each (a TX+ and TX-, and a RX+ and RX-); this is called twisted pair and (just like in twisted pair Ethernet) allows for longer wire runs with less noise from other wires. The other data pins are for ground, which also assist with noise elimination. So SATA doesn't need more data pins.

Power, on the other hand, supplies 3.3 V, 5 V, 12 V, and ground. Not to mention extra pins (not present in all connectors) for hotplugging, activity indication, and staggered spinup. As to why so many? Wikipedia again:

Each voltage transmits through three pins ganged together, because the small contacts by themselves cannot supply sufficient current for some devices. (Each pin should be able to provide 1.5 A.)

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