What is secondary memory device?

Secondary memory, also called auxiliary memory or mass storage, consists of devices not directly accessible by the CPU. Hard drives, floppy disks, tapes, and optical disks are widely used for secondary storage. The input and output of these devices is much slower than for the semiconductor devices that provide the computer's primary memory. Although access times (i.e., the time to read or write information) are slow as compared to that of primary memory, secondary memory devices have important features that are unmatched by primary memory. First, most secondary storage devices are capable of containing much more information than is feasible for primary memory (hence the use of the term "mass storage" as a synonym for secondary memory). A second, and essential, feature of secondary memory is that it is non-volatile. This means that data is stored with or without electrical power being supplied to the device, as opposed to RAM, which can retain its data only so long as electrical power is present.