The document discusses the various types of memory in digital computers, including semiconductor, magnetic, and optical memory. It elaborates on specific optical formats like CD-ROM, WORM, and DVDs, detailing their storage capacities, access times, and writing methods. The advantages of these memory types include high storage density, data integrity, and the ability to read or write data as needed.

1. BY-Sonal Srivastava
B.Tech (CSE)
4th Sem.

2. • Memory is a storing device.
• It is used to store data and information.
• It is an essential component of a digital
computer.

3. There are three types of memory-
 SEMICONDUCTOR MEMORY
 Ram
 Rom
MAGNETIC MEMORY
OPTICAL MEMORY

4.  Laser beam is used to write or read
information.
 It has a very high storage density and data
integrity.
 It is relatively inexpensive and has a long
life.
 Optical disk is removable from the
computer.

5. 1. CD-ROM(Compact disk read only memory)
2. WORM(write once read many)
3. MAGNETO-OPTICAL DISKS
4. DVD-ROM,DVD-R & DVD-RAM
5. FLOPTICAL DISKS

6.  It is Compact Disk Read only memory.
 Information is written to the disk by burning
pits on the disk surface with controlled laser
beam.
 The disk is made of resin,such as
polycarbonate.
 It is coated with a highly reflective surface
,usually aluminium.
 CD-ROMs do not use concentric tracks .
 They use single spiral tracks .

7.  The disk size is 5.25 inch diameter.
 track density is 16000 tracks per inch.
 The capacity of CD-ROM is 600 MB,2048
bytes of information are stored per sector.
 Access time is about 80 ms of new disks.
 Access time for earlier disks is 250 ms.
 Data transfer rate is about 4800KB/sec.

8. • The user can write data only once.
• A laser beam is used to write information on
the disk.
• The written data can be read as many times
as desired.
• They store permanent information for record.
• One can rewrite modified or some new
information to another portion of the disk.
• One can not modify data which has already
been written.

9.  The size of disk is 5.25 inch diameter.
 The capacity of WROM is 650 MB.
 It has high capacity better reliability and
longer life.
 It runs at constant speed to reduce access
time.
 Its tracks are concentric circles .
 Each track is divided into a number of sectors.
 It has longer access time compared to hard
disks.

10.  Also known as erasable optical disk.
 It is a read write laser assisted magnetic memory.
 Info can be written to or read from the disk as many
times as required.
 The read/write head contains a laser beam and a
current coil.
 A magnetic field perpendicular to the disk surface
can be produced by passing current through coil.
 It writes info when magnetic material is heated by
laser beam.

11.  Available in 5.25 inch or 3.5 inch diameter.
 Storing capacity of 5.25 inch disk is 650
MB,5.2GB etc.
 Capacity of 3.5 inch disk is 1.3 GB.
 It has high density,long life,portability &
better reliability.
 It is slower in access.
 Data transfer is slower as compared to hard
disk.

12.  These are high capacity floppies.
 They use laser beam to mark tracks and sectors.
 They have more tracks & sectors than ordinary
floppies.
 Read/write operation is done as in ordinary
floppies.
 These are removable.
 It uses surface coating of barium ferrite.

13.  It is a kind of magneto-optical disk.
 Its speed is same as magneto-optical disk.
 It uses a 3.5 inch disk shell.
 Its capacity is about 120 MB.
 A floptical drive can also read/write standard
3.5 inch floppies..

14.  These are digital versatile disks ROMs.
 They store much more data as compared to
CD-ROMs.
 It is double sided & have dual layers.
 It contains a thick polycarbonate plastic which
provides a base for other layers.
 The next layer is a thin opaque layer of
reflective material.
 Then a thin layer of transparent film & a
protective layer is used.

15.  It is a read/write optical memory.
 It uses phase change technology to read,write
and erase data.
 The laser beam is focussed on a reflective
layer made of silver ,indium & tellurium
embedded in a plastic base.
 In the normal state the reflective layer has
crystalline structure.
 To erase the data low energy laser beam is
used.

16. DVD-R is once writable optical disk.
 It is a recordable DVD.
 It is similar to WORM.
 Its size,capacity & speed is same as
WROM.
DVDs use shorter wavelength of light
than CD does.
The capacity of DVD-ROMs is 4.7 to 17
GB.