Any computer needs a hard disk to hold the operating system and any other types of work that you do. As recently as a few years, ok perhaps 10, the only question was how large of a hard disk do you need and the only hard disks were mechanical.
There were a few different types, but basically the difference was how fast were the platters spinning which affects how quickly the data can be returned. For mechanical hard disk the data throughput rate was about 100mb per second.
The biggest advance was the invention of the SATA SSD which is a huge advance as the hard disk is just a bank of memory. The delays due to spinning disks is eliminated and the throughput skyrocketed to about 500mb per second. This transfer rate actually approached the limits of the SATA interface.
The most recent breakthrough was when the NVME M.2 SSD hard disks. The difference was the change of the electroncs from the SATA to the PCI bus. This resulted in another giant breakthrough to data transfers of from 2100mb per second.
History and comparison of hard disks up through NVME SSD disks.
Visual demonstration of different disk technology in load times
