What is a hard drive?
A computer hard drive (or a hard disk or HDD) is one kind of technology that stores the operating system, applications, and data files. A computer hard disk drive (HDD) is a non-volatile data storage device. Non-volatile refers to storage devices that maintain stored data when turned off.
5 Benefits of purchasing a hard drive

Increase your storage capacity. What seems like more than adequate storage space now may seem miniscule in just a few months, so think to the future when you buy an external hard drive.
an external hard drive can be used as a backup. If your hard drives crashes you can have a spare.
Using an external drive as your boot (or main) drive can speed up the performance .
A hard drive can be seen as data on the go
Getting your external drive repaired might take less time and cost less than repairing the internal drive on your computer.