Primary storage: is the storage provided
by memory in a computer system
Secondary storage: is storage provided
by peripheral devices other than memory
Secondary storage: is required in a
computer system for three reasons:
1.The content of memory is usually volatile, which
means that if power is disconnected the data is
2. The capacity in megabytes of memory is limited
3. Memory is more expensive than secondary
These devices are used to store large amount of data
It differs from primary storage in that it is not directly
accessible by the CPU. So they need more access time
and thus are much slower.
It is broadly of two types-
1) MAGNETIC MEDIA
Magnetic storage uses different patterns
of magnetization in a magnetizable material to store data
It is a form of non-volatile memory
HARD DISKS and FLOPPY DISKS are such devices
It stores information on
one or more continuously
spinning disks which are
coated with magnetic
Information is recorded
by magnetic heads
called access arms.
These days, hard disks
have storage capacity
between 80 to 300 GB.
It is made of a flexible
substance called Mylar.
It has a magnetic surface
for recording data.
It stores upto 1.44 MB of
It cannot include graphics
or pictures within it.
All floppy disks must be
formatted before data can
be written on it.
Optic devices are generally circular disc which can
contain data encoded on a special material on one of its
The encoding pattern follows a continuous, spiral path
covering the entire disc surface and extending from the
innermost track to the outermost track.
These are broadly of two types-
1) CDs and
CDs are very cheap and
store upto 700 MB of
They are of three types-
› CD-ROM (CD Read
› CD-R (CD
› CD-RW (CD
It is of the same size as a
CD but stores 15 times as
much information, is 20
times faster than it.
It can hold 17 GB of data.
It comes in three varieties-
DVD-ROM (DVD Read
DVD-R (DVD Recordable)
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