its details abt external memory

1. PRESENTED BY
VALEN
MOHSIN
BHAGYASHREE
MILAN

2. TYPES OF EXTERNAL MEMORY
 MAGNETIC DISKS
 OPTICAL DISK
 MAGNETIC TAPE
 DISK DRIVE

3. MAGNETIC DISK
• Magnetic disk is a circular platter constructed of
nonmagnetic material, called the substrate , coated with a
magnetisable material.
• Traditionally aluminum or aluminum alloy were used as
substrates but recently glass substrates have been
introduced.
• Data are recorded on and later retrieved from the disk via a
conducting coil named the head; in many system, there are
two heads, a read head and a write head.
• During a read or write operation, the head is stationary
while the platter rotates beneath it.

4. MAGNETIC DISK

5. OPTICAL DISK
 CD – Compact disk. A non-erasable disk that stores
digitized audio information and can record more than 60
minutes of playing time.
 CD-ROM – Compact disk Read Only Memory. A non-
erasable disk used for storing computer data of up to
650mb.
 CD-R – CD recordable. Similar to a CD-ROM. The user can
write data only once.
 CD-RW – CD Rewritable. Similar to CD-ROM. The user
can erase and rewrite to the disk multiple times.

6.  DVD- digital versatile disk. A technology for storing
large volume of video or other digital data of up to
4.7Gb.
 DVD-R – DVD recordable. The user can write to disk
only once.
 DVD-RW – DVD rewritable. The user can erase and
rewrite data to the disk multiple times.

7. OPTICAL DISK

8. MAGNETIC TAPE
• Tape system use the same reading and recording
techniques as disk system.
• The medium is flexible polyester tape coated with
magnetizable material.
• Today, virtually all tapes are housed in cartridges.
• Unlike the disk, the tape is in motion only during a
read and write operation.

9. MAGNETIC TAPE

10. DISK DRIVE
 Hard disk drives were introduced in 1956 as data
storage.
 In hard disk information is written to and read from a
platter as it rotates past devices called read-and-write
heads that operate very close (often tens of
nanometers) over the magnetic surface.
 The hard drive`s electronics control the movement of
the actuator and the rotation of the disk, and perform
reads and writes on demand from the disk controller.
 The capacity of hard disk drives is in megabytes,
gigabytes or terabytes.

11. HARD DISK

12. THANK YOU