SATA DATA and Power Connectors
This article assumes you have a modern motherboard that no longer has IDE connectors. IDE drives haven't featured in consumer computers for some time. The overwhelming majority of computers and motherboards sold in recent years will focus solely on SATA drives (with a few exceptions, of course). Let's familiarize ourselves with the SATA 7P connector and port.
The left connector is for data (typically a red cable), while the second powers your drive. It is possible to buy an all-in-one, 22-pin SATA 15P cable that combines both connectors (but is less flexible).
3. SATA Data and Power Cables
Your new HDD or SSD probably arrived with at least its interface cable (the red cable in our example images above and below). But your drive also needs power. That power usually comes in the form of a 4-pin Molex power connector with a SATA drive specific connector.
A SATA HDD can arrive with a range of input connectors, allowing you to choose between a SATA power connector (the empty port to the left of the red interface cable, below) or 4-pin Molex connector (the cable on the far right, below). You can choose either one but not both at the same time!
A reader notes that you should "never use the Molex (4-pin) to SATA power adapter" because "most hard drives and solid state drives require the orange 3.3V wire to board to supply power for the drive electronics." This may cause the drives to fail at spinning up or registering in the computer's BIOS, Device Manager, or Disk Management. Thank you for the heads-up, Doc!
Consequently, some modern HDDs have done away with 4-pin Molex power inputs and now offer just a SATA power input. A SATA SSD will arrive with only a SATA power connector and a data transmission cable.