Hard Disc use disc to record data, and there are Read/Write heads and a Motors to Rotate the Discs and Heads. So there are many mechnical parts which require more power to drive and would fail with time.
Flash Drive or Solid Sate devices are the current day technology which use flip-flops to store data and have no motors or moving parts and is therefore less likely to fail. It is virtually weightless, retains data without a power supply, is faster than a hard drive, does not generate significant heat, and requires little power.
Flash Storage gives upto four times the performance of a traditional hard drive. It takes seconds to start up, apps launch quickly through flash.
Hard Drives have moving parts, they make some sound when reading and writing. While Flash memory is silent.