Secondary storage (or external memory) - is not directly accessible by the CPU. Secondary storage does not loose the data when the device is powered down and is typically less expensive than primary storage. Data is kept for a longer time in secondary storage.
A hard disk is part of a unit, often called a "disk drive," that stores and provides relatively quick access to large amounts of data. Computers typically come with a hard disk that contains gigabyte s of storage
Floppy Disk – (or diskette) is a removable disk that everyone is familiar with. Since it has a small capacity, it is typically used to store documents so that they can be used on more than one computer.
Optical Disks are read using laser beams and stores data in tracks. Optical discs are most commonly used for storing music (e.g. for use in a CD player ), video (e.g. for use in a DVD player ), or data and programs for personal computers
CDs - is an optical disc used to store digital data . It was originally developed to store sound recordings only, but later it also allowed the protection of other types of data .
DVDs (Digital Versatile Disc or Digital Video Disc)
DVD , is an optical disc storage media format, and was invented in 1995 . Its main uses are video and data storage. DVDs are of the same dimensions as compact discs ( CDs ), but store more than six times as much data.