If you just built a PC, or added a brand new hard drive or SSD to an existing computer, you have to format it before you can actually store data on it. This is called 'initializing' the drive.

Reattach the smaller hard drive cable to the SSD, then use the other Torx screws to attach the bracketed SSD in the iMac. Tuck the thermal sensor’s body off to the edge of the SSD.

Step by step tutorial on how to format a Hard Drive or Disk. Use built-in tools such as Diskpart, CMD, Disk Management, etc, to format.

When you buy a new hard drive, it’s usually pre-formatted, so all you have to do is connect it to your Mac. But there may come a time when you need to format a hard drive.