what are Auxiliary Storage Devices ? (squential vs Random auxiliary storage)

             Auxiliary storage, secondary storage, or external storage are devices that store noncritical system data like documents, multimedia and programs, which are used whenever they are required.

These files are invoked from the auxiliary storage when needed and then transferred to the primary storage so that the CPU can process them.The results of the process can also be sent back to the auxiliary storage for later retrieval.These storage devices hold data and programs for future use and are considered nonvolatile storage that retains information even when power is not available.The best example of auxiliary storage is hard disk drives and optical storage media like CDs, DVDs, and Blue ray.Other auxiliary storage belongs to the peripheral devices category as well, such as flash drives and any type of memory card.ž Auxiliary storage devices can be categorized in two types based on data access.

 1.Sequential Access
 2.Random Access

Sequential Access:
        Data are accessed sequentially.
                Data access time is more as to read particular data all preceding data must be read.
                Involves lower number of seek operations.
        Delivers high rate of throughput.
                      E.g. magnetic  tapes

Random Access:

Data can be accessed randomly.

Data access time is less as data on any location can be accessed directly.

Delivers lower rate of throughput.

E.g. magnetic disks, optical disks