A Hard Disk Drive (popularly called Hard Disk or HDD) is a hardware found inside of computers and its used to store files for the Operating system running in the computer, software programs and user’s personal data and files. A computer system will never work without an HDD installed in it and the HDD will also not run an operating system (OS) without being formatted or prepared by creating partitions (either MBR or GPT).
The Hard disk drive is a secondary storage device that permanently stores and retrieves data on a computer. Data is written on an HDD using a magnetic head located the air-sealed casing of the drive. HDDs could be Internal or External.
The internal Hard disk drive (HDD) seats in a drive bay inside the computer and connected to the mother board using a SATA, ATA or SCSI cable and are powered by a connection to the power supply unit (PSU) in the computer.