2. Secondary Storage
A computer has the ability to store its program,
data/information and the intermediate and final results its
calculations.
In this unit we can permanently store data in the form of
recordings on magnetic materials. Here data is recorded in the
form of
binary digits i.e.(1,0) called bits. Secondary
storage is also called auxiliary storage, external
storage, backup storage, long-term storage.
So a secondary device is a device in which data can be
introduced, held and can be obtained some other time.
3. A secondary storage has following four purpose:
1.
It provides long-term storage to data/information
that has not been used for many time.
2.
It give additional memory to computer to save data
and provides backup storage to main memory.
3.
It speeds up the accessing of the data/information
that is not possible in case of using only main
memory.
4.
It provides permanent storage to data/information
so that electricity failure or switching off of
computer does not harm data/information.
4. Types of Storage Device
There are several types of devices most of them are
magnetic. Some are efficient but too expensive for
many computer, some have extra large capacity
others are fast. Few types of them are as under:
1.
Magnetic Disks
2.
Magnetic Tape
5. Magnetic Disks
It is commonly used as secondary storage.
It is a circular plate coated by iron oxide and
protected in protective jacket.
Here data is stored in the form of binary digits as
magnetic spots.
Few types of magnetic disk are as under:
1.
2.
3.
Floppy disk
Compact Disk (C.D)
Hard Disk
6. Floppy Disk
It’s a flat circular plate of thin plastic coated by iron
oxide enclosed in plastic or cardboard jacket having a
small window form there we can access the disk and
read or write data/information.
There are two types of floppy:
1st is 51/4 inches capable of storing
1.2 MB data
2nd is 31/2 inches capable of storing 1.44 MB data.
7. Compact Disk (C.D)
It is a plastic disk relative harder than floppy disk having 4.75 inches in
diameter.
Its one surface is coated by iron oxide on which we can store 700 MB
of data/information or 80 minutes of music.
It works as read only storage device.
We can only read data
but cannot write on it
Therefore it is called
CD-Rom .it is used for
storing applications, games
and operating software etc.
8. Hard Disk
It is a metallic disk thick than Cd-rom and floppy
disk.
It is enclosed in an air tight case to exclude dust.
Therefore it is called fixed disk
Here data are recorded as series of magnetic spots
pattern and can store
a huge amount of data.
Hard disk
9. Magnetic tapes
It is a tape coated with iron oxide used for magnetizing data on it as
magnetic spots.
It is in different width for different computer.
They store large data in fairly compressed form.
It can carry up to a maximum of 9 magnetic spot in vertical column.
It has 9 rows called tracks. Each track has its read/writing head for
playing back or recording the information. here data is in the form of
large continuous stream.Following are different types of tapes:
1.
Tape cartridge
2.
Tape cassettes
10. Tape Cartridge
It is a plastic box having long strip of magnetic tape
on which a permanent program is stored.
Like CD-ROM we can only read data on it but can
not write on it i.e. a user can not save any thing on it,
only manufacturer can install data on it. Therefore it
is called ROM Cartridge.
11. Tape Cassette
It also contain a magnetic strip in a plastic box
having shape like an audio cassette.
Here data is stored in sequential order,if we want to
reach a particular data then we have to pass all data
to reach that point.
It is little different from audio cassette because on
audio cassette music is stored in the form of audio
tones but in tape cassette data is stored
in the form of binary digits (bits).
