Secondary storage is required for computers for three reasons: primary storage is volatile, has limited capacity, and is more expensive than secondary storage. Secondary storage includes magnetic media like hard disks and floppy disks, as well as optical media like CDs and DVDs. These devices store large amounts of data permanently but are not directly accessible by the CPU, so they have slower access times than primary storage.

4.  Primary storage: is the storage provided
by memory in a computer system
e.g. ROM/RAM.
 Secondary storage: is storage provided
by peripheral devices other than memory

14.  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
lost.
2. The capacity in megabytes of memory is limited
3. Memory is more expensive than secondary
storage.

15.  These devices are used to store large amount of data
permanently.
 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
2)OPTIC MEDIA.

16.  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

17.  It stores information on
one or more continuously
spinning disks which are
coated with magnetic
material.
 Information is recorded
by magnetic heads
called access arms.
 These days, hard disks
have storage capacity
between 80 to 300 GB.
Aaccess arm

18.  It is made of a flexible
substance called Mylar.
 It has a magnetic surface
for recording data.
 It stores upto 1.44 MB of
data.
 It cannot include graphics
or pictures within it.
 All floppy disks must be
formatted before data can
be written on it.

19.  Optic devices are generally circular disc which can
contain data encoded on a special material on one of its
flat surfaces.
 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
2) DVDs.

20.  CDs are very cheap and
store upto 700 MB of
data.
 They are of three types-
› CD-ROM (CD Read
Only Memory)
› CD-R (CD
Recordable)
› CD-RW (CD
Rewritable)

21.  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
Only Memory)
 DVD-R (DVD Recordable)
 DVD-RW (DVD
Rewritable)