What is HDD and SSD, and what are the difference?

The technology behind hard disk drives (HDD) is well known and well tested. HDDs rely on spinning disks, or platters, to read and write data. Solid state drives (SSD) use flash memory to deliver superior performance and durability. Without moving parts, SSDs are more durable, run cooler and use less energy. They are similar in their physical specifications, but they store data very differently.