Secondary Storage Secondary Storage UnitUnit

Secondary StorageSecondary StorageIts TypeIts Type

Secondary StorageSecondary Storage

A computer has the ability to store its program, A computer has the ability to store its program, data/information and the intermediate and final data/information and the intermediate and final results its calculations.results its calculations.

In this unit we can permanently store data in the In this unit we can permanently store data in the form of recordings on magnetic materials. Here form of recordings on magnetic materials. Here data is recorded in the form of data is recorded in the form of binary digits binary digits i.e.(1,0) called i.e.(1,0) called bits. bits. Secondary storage is also Secondary storage is also called called auxiliary storage, external storage, auxiliary storage, external storage, backup storage, long-term storage.backup storage, long-term storage.

So a secondary device is a device in which data So a secondary device is a device in which data can be introduced, held and can be obtained can be introduced, held and can be obtained some other time.some other time.

A secondary storage has following four A secondary storage has following four purpose:purpose:

1.1. It provides It provides long-termlong-term storage to storage to data/information that has not been used for data/information that has not been used for many time.many time.

2.2. It give additional memory to computer to It give additional memory to computer to save data and provides backup storage to save data and provides backup storage to main memory.main memory.

3.3. It speeds up the accessing of the It speeds up the accessing of the data/information that is not possible in case data/information that is not possible in case of using only main memory.of using only main memory.

4.4. It provides permanent storage to It provides permanent storage to data/information so that electricity failure data/information so that electricity failure or switching off of computer does not harm or switching off of computer does not harm data/informationdata/information..

Types of Storage DeviceTypes of Storage Device

There are several types of devices There are several types of devices most of them are magnetic. Some most of them are magnetic. Some are efficient but too expensive for are efficient but too expensive for many computer, some have extra many computer, some have extra large capacity others are fast. Few large capacity others are fast. Few types of them are as under:types of them are as under:

1.1. Magnetic DisksMagnetic Disks

2.2. Magnetic TapeMagnetic Tape

Magnetic DisksMagnetic Disks It is commonly used as secondary It is commonly used as secondary

storage.storage. It is a circular plate coated by iron oxide It is a circular plate coated by iron oxide

and protected in protective jacket.and protected in protective jacket. Here data is stored in the form of binary Here data is stored in the form of binary

digits as magnetic spots.digits as magnetic spots.Few types of magnetic disk are as under:Few types of magnetic disk are as under:1.1. Floppy diskFloppy disk2.2. Compact Disk (C.D)Compact Disk (C.D)3.3. Hard DiskHard Disk

Floppy DiskFloppy Disk

It’s a flat circular plate of thin plastic coated It’s a flat circular plate of thin plastic coated by iron oxide enclosed in plastic or by iron oxide enclosed in plastic or cardboard jacket having a small window cardboard jacket having a small window form there we can access the disk and form there we can access the disk and read or write data/information.read or write data/information.

There are two types of floppy:There are two types of floppy:

11stst is 5 is 51/41/4 inches capable of storing inches capable of storing

1.2 MB data1.2 MB data

22ndnd is 3 is 31/21/2 inches capable of storing 1.44 MB inches capable of storing 1.44 MB data. data.

Compact Disk (C.D)Compact Disk (C.D) It is a plastic disk relative harder than floppy disk It is a plastic disk relative harder than floppy disk

having 4.75 inches in diameter.having 4.75 inches in diameter. Its one surface is coated by iron oxide on which Its one surface is coated by iron oxide on which

we can store 700 MB of data/information or 80 we can store 700 MB of data/information or 80 minutes of music.minutes of music.

It works as read only storage device.It works as read only storage device. We can only read dataWe can only read databut cannot write on itbut cannot write on itTherefore it is calledTherefore it is calledCD-Rom .it is used for CD-Rom .it is used for storing applications, games storing applications, games and operating software etc.and operating software etc.

Hard DiskHard Disk

It is a metallic disk thick than Cd-rom It is a metallic disk thick than Cd-rom and floppy disk.and floppy disk.

It is enclosed in an air tight case to It is enclosed in an air tight case to exclude dust. Therefore it is called exclude dust. Therefore it is called fixed diskfixed disk

Here data are recorded as series of Here data are recorded as series of magnetic spots pattern and can store magnetic spots pattern and can store

a huge amount of data.a huge amount of data.

Hard diskHard disk

Magnetic tapesMagnetic tapes It is a tape coated with iron oxide used for It is a tape coated with iron oxide used for

magnetizing data on it as magnetic spots.magnetizing data on it as magnetic spots. It is in different width for different computer.It is in different width for different computer. They store large data in fairly compressed form.They store large data in fairly compressed form.It can carry up to a maximum of 9 magnetic spot in It can carry up to a maximum of 9 magnetic spot in

vertical column.vertical column.It has 9 rows called tracks. Each track has its It has 9 rows called tracks. Each track has its

read/writing head for playing back or recording read/writing head for playing back or recording the information. here data is in the form of large the information. here data is in the form of large continuous stream.Following are different types of continuous stream.Following are different types of tapes:tapes:

1.1. Tape cartridgeTape cartridge2.2. Tape cassettesTape cassettes

Tape CartridgeTape Cartridge

It is a plastic box having long strip of It is a plastic box having long strip of magnetic tape on which a permanent magnetic tape on which a permanent program is stored.program is stored.

Like CD-ROM we can only read data Like CD-ROM we can only read data on it but can not write on it i.e. a on it but can not write on it i.e. a user can not save any thing on it, user can not save any thing on it, only manufacturer can install data on only manufacturer can install data on it. Therefore it is called ROM it. Therefore it is called ROM Cartridge.Cartridge.

Tape CassetteTape Cassette It also contain a magnetic strip in a plastic It also contain a magnetic strip in a plastic

box having shape like an audio cassette.box having shape like an audio cassette. Here data is stored in sequential order,if Here data is stored in sequential order,if

we want to reach a particular data then we want to reach a particular data then we have to pass all data to reach that we have to pass all data to reach that point.point.

It is little different from audio cassette It is little different from audio cassette because on audio cassette because on audio cassette musicmusic is is stored in the form of audio tones but in stored in the form of audio tones but in tape cassette data is storedtape cassette data is stored

in the form of binary digits (bits).in the form of binary digits (bits).