Storage Devices


Secondary storage is also known as auxiliary memory or external memory or back up storage. The secondary storage devices are used in most computer systems to supplement the limited storage capacity of the primary memory section. This is similar to our keeping a diary or a note book when our memory is incapable of storing many facts and figures. We refer to our diary whenever we need the data.

Secondary Storage Devices are
1. Magnetic tape
2. Magnetic disks
3. Compact Disk Read Only Memory (CD-ROM)
The data is either stored or erased by laser beam to CD-ROM.

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Magnetic Tape:
Magnetic tap is one of the most popular storage medium for larger data that are sequentially accessed and processed. The tape is plastic ribbon usually 1/2 inch wide that is coated as one side with magnetic material. It is similar to the tape used on a tape recorder except that is higher quality and more durable.

Advantages
(a) Unlimited Storage Capacity
(b) Low Cost
(c) Portability

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Magnetic Disks :
A magnetic disk is a, circular plate coated on both sides with a magnetic material. It is very similar to a gramophone record. Each disk consists of a number of invisible concentric circles called tracks. Each track is further sub-divided into sectors. Information is recorded on the tracks of a disk surface in the form of invisible tiny magnetic spots. The presence of a magnetized spot is represents as '1 ' bit and its absence represented a '0' bit.

Magnetic disks are two types:
1. Floppy Disk
2. Hard Disk

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Floppy Disk:
The floppy disk is a flexible, circular shaped medium with a magnetic coating on it. It is sensitive to touch and dust. A floppy disk enclosed in a leather jacket to protect it from external damage and dust.

There are three types of floppy’s available.
1) 3.5" Floppy Disk ( Capacity 1.44 Mb ) introduced : Sony
2) 5.25" Floppy Disk ( Capacity 1.2 Mb ) introduced : Shugart
3) 8.0" Floppy Disk ( Capacity 100 Kb ) introduced : IBM

The 3.5" disks are the most popular and commonly used.

On the Basis of Capacity they are of two types:
(a) High density
(b) Low density

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Hard Disk:
Hard Disk is also a secondary storage device. The hard disk storage system was developed to reduce the problem of diskettes frequently getting damaged.

Hard disks come in different capacities. The minimum capacity is generally twenty times that of a high density floppy disk in terms of storage capacity. The hard disk is generally fixed inside the computers.

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Compact Disk Read Only Memory (CD-ROM):
CD-ROM disks are made of reflective metals. CD-ROM is written during the process of manufacturing by high power laser beam. The storage density is very high, cost is very low and access time is relatively fast.

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Input/Output:
The term Input/Output is used to describe any program, operation or device that transfers data to or from a computer and to or from a peripheral device. Every transfer is an output from one device and an input into another. Devices such as keyboards and mouse are input-only devices while devices such as printers are output-only. A writable CD-ROM is both an input and an output device.

Input Devices:
Input device is a hardware device which is use to input data, image, and video to the computer.

Input Devices:
Digital camera
Keyboard
Microphone
Mouse
Scanner
Web Cam
Light pen
Joy stick
Etc.
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Out put Devices:
Output device is a hardware device which is use to receives or displays output from a computer

Output Devices:Monitor
Printer
Plotter
Speaker
Projector
Etc.


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