M E M O RY

UNIT OF
COMPUTER
WHAT IS
MEMORY?
Memory unit is the
unit that perform
operation which holds
data and programs.
Memory is an essential
component of digital
computer. There are
different types of
memory that are:
• Semiconductor
memory
• Magnetic memory
PRIMARY
MEMORY
Primary memory of a
computer system (known
as Main Memory) stores
pieces of program
instructions and data,
intermediate results of
processing, and recently
produced results of those
jobs on which the
computer system is
currently working. Primary
memory is volatile in
nature, it loses information
as soon as computer
system switches off or
CACHE
MEMORY
Cache Memory is an extremely
fast, small memory between CPU
and main memory whose access
time is closer to the processing
speed of CPU. It acts as high speed
buffer between CPU and main
memory and computer systems
use it to store temporarily very
active data and instructions during
processing. Since cache memory is
faster than main memory,
system’s performance improves
considerably when the system
makes those data and instructions
available in cache that processes
RANDOM
ACCESS
MEMORY
(RAM)
RAM stands for Random Access
Memory and is often called the
memory or main memory. It is
the working space used by
computer to hold the program
that is currently running along
with necessary data and
instructions. RAM is used for:
• Kernel of running operating
system.
• Data and instruction
currently being processed.
• Data and instruction waiting
to be processed.
 TYPES OF
• RAM
Dynamic RAM (DRAM): DRAM
is the most common and
cheapest type of memory
chip. It is made of capacitors
which is capable of storing
the electric charge. Due to
leakage of charges, the
capacitors discharge
gradually and the memory
cells lose their contents. It is
slower than SRAM but it is
dense, smaller in size and
less expensive.
• Static RAM (SRAM): SRAM is
made of transistors. It is
called static because it can
READ ONLY
MEMORY
(ROM)
ROM stands for ‘Read Only
Memory’ and it is called ROM
because only read operation
can be performed on it. The
user can not write anything
into ROM. It is non-volatile
memory chip in which data is
stored permanently. The binary
information stored in ROM is
written permanently by the
manufacturer and it cannot be
altered. The program such as
TYPES OF ROM
PROM: PROM stands for Programmable Read Only Memory
Initially it is the blank chip which can be written or
programmed only one time by using a special machine
called ROM programmer or ROM burner. Once the PROM is
written, it cannot be modified and becomes ROM.
EPROM: EPROM stands for Erasable Programmable Read
Only Memory. It is a special chip which can be re-
programmed to record different information. The data and
information are erased by exposing it to intense ultra violet
light.
EEPROM: EEPROM stands for Electrically Erasable
Programmable Read Only Memory This type of chip can be
erased and reprogrammed repeatedly with special electrical
pulses. It does not require a special device to write into it.
SECONDAR
Y MEMORY
Secondary memory is
non-volatile memory
and has lower cost per
bit, but operates
generally at speeds far
slower than primary
memory. Computer
system use its
primarily to store large
volume of data
permanently, which
they transfer partially
MAGNETIC
MEMORY
Magnetic memory is the
memory in which data
are stored in magnetic
sensitive material. To
perform read and write
operation the head is
utilized which is
demagnetized and
magnetized accordingly.
The magnetic memory
are of Magnetic Disk and
Magnetic Tape and
Magnetic Drum.
M A G N E T I C M E M O RY
2. Floppy Disk: The floppy disk needs a
special device to manage and manipulate
data in it and this device is called Floppy Disk
Drive (FDD). The FDD has read/write head to
read from and write data to floppy disk.
3. Magnetic
Generally tape:
the It isdrive
floppy a secondary
in namedstorage
as A: or
device
B: driveofincomputer
PCs which is made of Mylar (a
type of plastic material coated with magnetic
material only one side of the tape. It is a low
cost storage device and it has large storage
capacity. It is mainly used to back up the
large amount of data and information It is
also used to transfer data from one computer
to another. The main drawback of it is that we
MAGNETIC
MEMORY
4.Magnetic Drum: A magnetic
drum, referred to as drum, is a
metal cylinder coated with
magnetic iron-oxide material
on which data and programs
can be stored. The tracks on a
magnetic drum are assigned
to channels located around the
circumference of the drum,
forming adjacent circular
bunds that wind around the
drum. Magnetic drums are able
to retrieve data at a quicker
rate than tape or disk devices
but are not able to store as
6. OPTICAL
DISK
Optical memory is a non-
volatile secondary storage
medium. It is a flat round disk.
It is made of plastic
polycarbonate material coated
with aluminum alloy and a very
fine laser beam is projected on
the reflecting surface to read
data from the disk The intensity
of the reflected light of the
laser changes as it encounters
a pit and land. The land reflects
higher intensity light than pit.
The higher and less intensity
fight is translated as 1 and 0
TYPES OF OPTICAL DISK
a. CD: CD stand for ‘Compact Disk’ and it has following types:

i. CD-ROM: CD-ROM stands for ‘Compact Disk Read Only Memory. Because of the optical storage
medium, laser beam is used to access data from the disk. It can store about 700MB of data or
80 minutes of video or audio. CD-ROM can not be written again once they are written. The users
can not write new data or modify the existing data to the CD-ROMs.

ii. CD-R: CD-R stands for Compact Disk Recordable and initially it is a blank disk. Unlike CD-
ROM, it can be written only once with the laser beam by using a special device called CD-Writer
or Burner. After it is written, it can not be erased or modified.

iii. CD-RW: CD-RW stands for ‘Compact Disk ReWritable. As the name suggests, it can be erased
and written many times like magnetic disk. It also needs a special device called CD-Writer to
write into it. The main advantage of CD-RW is that it can be erased and re-written.
TYPES OF OPTICAL DISK:
b. DVD: DVD stands for ‘Digital Versatile Disk’ or ‘Digital Video Disk. It is also a type of
optical memory device which has a very large storage capacity. It is also considered as
the improved form of CD-ROM. DVD also uses the same technology as a CD-ROM for
needing and writing data. Because of its huge storage capacity and vivid picture
quality, movies, PC games, educational software. Encyclopedia etc. are being stored
and distributed to a large number of people. It is also available in the form of DVD-
ROM, DVDR and DVDRW

c. Blue-ray: Blu-ray Disc is a digital optical disk storage format. It is designed to

supersede the DVD format, capable of storing several hours of video in high-definition
(HDTV 720p and 1080p). The main application of Blu-ray is as a medium for video
material such as feature films and for the physical distribution of video games for the
PlayStation 3, PlayStation 4. PlayStation 5, Xbox One and Xbox Series X. The name
“Blu-ray” refers to the blue laser (which is actually a violet laser) used to read the disc,
which allows information to be stored at a greater density than is possible with the
longer-wavelength red laser used for DVDs.
STORAGE DEVICE
7. External Storage device: The storage devices which are not permanently
attached to the computer system are called external storage devices.
External storage devices are especially used to backup the important data
and programs and to transfer them from one computer to another computer.
The examples of external storage devices are Removable Hard Disk, Pen
drive, Zip drive, Jaz drive etc.

8. Memory stick: Memory Stick is a type of flash memory developed by Sony.

It is used to store data for digital cameras, camcorders, and other kinds of
electronics. Because Memory Stick is a proprietary Sony product, it is used by
nearly all of Sony’s products that use flash media. Unfortunately, this also
means Memory Stick cards are incompatible with most products not
developed by Sony.