Optical, Magnetic and Solid State
Storage of data on an optically readable medium. It's recorded by marks in a pattern which can be read by light, usually a laser beam on a spinning disk. Examples are CDs and optical jukeboxs.
Storage of data that is based on electronic circuits so has no moving parts - no tape, spinning disks. They use flash memory which is non-volatile but the data in it can be erased or changed. Examples are USB sticks, memory cards and smart cards.