Any mechanism that operates without any moving parts is considered to be solid state. A Solid State Drive stores data electronically and is a device in the computer.

The Hard Disk Drive has been the standard storage mechanism since the late 1980s, it has spinning disks and an arm that moves back and forth like a record player. This has been replaced by microchips that are able to electronically store information. Since there are no moving parts in a Solid State Drive it is less prone to failure. It is not immune to failure though, the technology used by the chips do have a finite life, but can still last many years under heavy use before needing to be changed out. The rate of failure is far less that with spinning disk drives.

Although Hard Disks with spinning platters like record players have higher storage capacity so they are not completely obsolete, but their days are numbered.