secondary storage devices

Limitations of Primary Memory:
Limited capacity because the cost per bit of storage is high

Volatile - data stored in it is lost when the electric power is turned off or interrupted.

So as a result additional memory called auxiliary memory or secondary memory is used.

Following are the features of Auxiliary or Secondary Storage:

1. Permanent or Non-volatile Storage: The data which is stored in those devices is not lost when the power is switched off. The data is retained.

2. Voluminous data: We can store volumes of data and instructions in these devices. This makes these devices very useful.

3.Relatively Cheaper: These storage devices are relatively cheaper and cost effective than primary memory of the CPU.

4. Portable: These devices act as a portable media for transferring data from one system to another. The access to data stored can be in serial order or random depending upon type of secondary storage devices.

Sequential and direct access Devices:

Arrival at the desired storage location may be preceded by sequencing through other locations

Data can only be retrieved in the same sequence in which it is stored

Access time varies according to the storage location of the information being accessed

Magnetic tape is a typical example of such a storage device

Direct-Access Devices:

Devices where any storage location may be selected and accessed at random

Permits access to individual information in a more direct or immediate manner

Approximately equal access time is required for accessing information from any storage location

Suitable for direct processing applications such as on-line ticket booking systems, on-line banking systems

Magnetic, optical, and magneto-optical disks are typical examples of such a storage device

Best example to differentiate b/w sequential and direct access is the audio cassette and compact