Memory can be classified as primary or secondary. Primary memory (RAM) is directly accessible by the CPU and is used to store currently running programs and data. Secondary memory (hard disks, SSDs) is used for long-term storage and requires data to be transferred to primary memory for access. RAM types include DRAM and SRAM, while ROM is non-volatile. Cache memory improves CPU performance. Input devices like keyboards are used to input data into the computer's primary memory.

1. Memory and its Classification
Figure: Memory Hierarchy

2. Primary memory/ Primary Storage
Devices
• Memory is the most essential part of
a computer
• There are two kinds of computer
memory :Primary and secondary
• Memory is used for storing both
instructions to be executed and data.
• The CPU accesses each location in
memory by using a unique number,
called a memory address

3. Primary Memory / Main memory and
its type
• The memory that is accessible
directly by the processing unit is
called primary memory.
• We can store and retrieve data much
faster with primary memory as
compared to secondary memory and
is more expensive than secondary
memory
• This data may come from an input
device like keyboard of from a
secondary storage device like hard

4. Primary Memory/Main Memory and
its type
• Primary memory used in our
computers are:
1. Random Access Memory(RAM)
2. Read only Memory
3. Cache Memory
4. Register

5. Random Access memory(RAM)
• This Memory is generally made up of
semiconductor device.
• RAM or Random Access Memory also
known as volatile memory is a form
of computer data storage device
which stores most commonly
accessed data in the computer.
• CPU cannot use data and instruction
directly from hard disk, it must be
loaded into RAM before CPU uses it.
• There are two types of RAM i.e

6. DRAM
• DRAM stands for Dynamic RAM.
• It is Cheaper than SRAM
• Data Density of DRAM is higher and
hence storage needs cost per bit is
relatively low.
• DRAM is made up of transistors and
capacitors. One transistor and one
capacitor is used to make a memory
cell.
• DRAM is slower than SRAM.

7. SRAM
• It stands for static RAM
• It is more expensive than DRAM.
• Data density of SRAM is lower and
hence store cost bit is high.
• SRAM is made up of transistors only.
Six transistors are used to make a
memory cell.
• SRAM is faster than DRAM

8. Read only Memory(ROM)
• ROM is the primary memory that stores some
standard processing programs supplied by the
manufacture to operate the personal computer.
• ROM is non-volatile memory because it does
not lose their content on failure of power
supply.
• CPU can only read the content of ROM but can
not change the content of ROM.
• The basic input/output program is stored in the
ROM that examines and initializes various
equipment when the switch is made ON.

9. Types of ROM
Others variations of ROM are :
PROM, EPROM, EEPROM

10. PROM (Programmable Read Only
Memory)
• Data stored permanently
• Retains the content when
the computer is turned off
• Manufactured as blank memory.
• To write onto a PROM chip,
you need a special device called a
PROM programmer or a PROM burner.

11. EPROM (Erasable Programmable
Read-Only Memory)
• An EPROM is special type of PROM
that can be erased by exposing it to
ultraviolet light.
• The Ultraviolet light clears its
content, making it to reprogram the
memory.

12. EEPROM(Electrically Erasable PROM)
• An EEPROM is a special type of PROM
that can be erased by exposing it to
an electrical charge and then it can
be reprogrammed.
• Requires data to be written or erased
one byte at a time.

13. Cache Memory
• Cache memory is the high speed
access memory.
• This memory is typically integrated
directly with CPU chip of placed on a
separate chip that has separate bus
interconnect with the CPU.
• much faster than RAM or main
memory and expensive.
• A computer can have several different
levels of cache memory.

14. Level 1 (L1) cache
• It is also called primary or internal
cache.
• It is built directly into the processor
chip.
• Ranging from 8KB to 64KB.
• It is fasted and most expensive
cache memory.
• CPU looks to L1 cache first for data.

15. Level 2 (L2) Cache
• It is slower than L1 cache.
• Its storage capacity is more, ranging
from 4-8MB.
• L2 cache is larger than L1, but take
longer to access.
• This cache is separate from
processor chip on the motherboard.

16. Registers
• The computer uses a number of special
memory called registers.
• Registers are fastest memory units used to
store data and instructions temporarily
that are used by CPU immediately.
• Once the instruction is executed or data is
used by CPU, registers are immediately
loaded by another instruction or data.
• Example of register are instruction
register, program counter, accumulator
etc.

17. Secondary Memory/ secondary
storage devices
• Secondary memory such as floppy disks, hard disk
etc is located outside the computer and CPU cannot
directly access the secondary memory.
• It is necessary to store hundreds of millions of bytes
of data for the CPU to process, therefore additional
memory is required in all the computer system.
• This memory is also called auxiliary memory
secondary storage.
• This type memory the cost per bit is low, however
the operating speed is slower than that of the
primary memory.
• Data are stored here on the permanent basis and
transferred to the primary storage.

18. Types of secondary memory
• Magnetic disks
• Magnetic Tape
• Flash Memory
• Optical storage

19. Magnetic Tape
• It is magnetically coated strip of
plastic on which data can be stored.
• Accessing data on tapes is much
slower than accessing data on disks
because it is sequential access
storage device.
• They are generally used for
long term storage and backup.
• It is similar to cassette tape recorder.

20. Magnetic Disk
• It is circular like disk and coated with
magnetic material.
• Magnetic disks are most popular for
direct access storage devices.
• In magnetic disk we can stored data
in the form of track.
• It uses a magnetization
process to write, rewrite
and access data.

21. Types of magnetic disks
• Hard disk
• Floppy disk

22. Hard disk
• Hard disk is the magnetic disk.
• A single hard consist of several platters.
• Each platters requires two read/write heads, one for
each side.
• All read/write heads are attached to a single access arm
so that they cannot move independently.
• Each platter has the same number of tracks.
• The tracks are divided into sections called sectors.
• Platters of hard disk spin thousands of times per second
and disk arm moves just back and forth.
• When the data access is required, first of all RW head is
positioned into track and waits for the required track.
• When the track comes under RW head ,data is
accessed.

23. Hard disk

24. Floppy disk
• Floppy disk is a soft magnetic disk that is commonly
used to move files between different computers.
• Also used to load new programs onto the computer,
store backup of data and small programs.
• It is slower to access data than hard disks and have
less storage capacity, but is less expensive and
portable.
• Flopping come in two basic sizes: 5.25inch and 3.5
inch and the most common 5.25 inch floppies were
360KB and 1.2MB and 3.5 inch hold 1.44 MB of data.
• Its internal structure and working mechanism is same
as that of hard disk.

25. Optical Disks
• Optical disks are the storage medium
from which data is read and to which
data is written with the help of laser
light .
• An optical disc is flat, usually circular
disc which encodes binary data in
the form of pits and lands on a
special material on its flat surfaces.
• There are two types of optical disks:
CD and DVD.

26. Compact Disk (CD)
• It is data storage format, which basically
means that it is used to store data.
• It is portable and its capacity usually ranges
form 650 to 750 MB.
• There are three basic type of compact disk
• CD-ROM: It stands for CD- read only memory.
CD-ROM is written during the process of
manufacturing by high power of laser beam.
and the data is permanent and can be read
any numbers times, but cannot be modified.

27. Compact disk
• WORM: It stands for write once,
Read-many(WORM).You can write
data onto a WORM disk, but only
once. After that, the WORM disk
behaves just like a CD-ROM.
• Erasable optical Disk (EO): These
are optical disks where data can be
written, erased and re-write.
Erasable optical disks are based on a
technology known as magnetic
optical .

28. Digital versatile Disk(DVD)
• DVD is primarily used to store movies or music.
• It is similar to a CD but has larger capacity.
• It has same physical appearance, But it
provides several times as much up to 4.7
gigabytes on one disc.
Blu-ray Disk: Blu-ray is an optical disk format
designed to display high definition video and
store large amount of data. Blu-ray is
successor to DVD.The format’s comes from the
fact that a blue laser reads from and writes to
the disk rather than red laser of DVD players .

29. Flash Memory
• Flash memory is a type of electronically erasable
read only memory. But may also be standalone
memory storage device such as a USB drives.
• Flash memory is a special type of EEPROM,
which is programmed and erased in large blocks
whereas EEPROM’s had to be completely erased
before being rewritten.
• It has very fast access time than hard disk drive.
• The two main types of flash memory are NAND
and NOR flash memory.
• NAND offers fast write/erase capability and
slower than NOR in the area of read speed.

30. Memory /SD card
• Memory card is a type of storage media that is often
used to store photos, videos or other data in
electronic devices.
• Devices that commonly use a memory card include
digital cameras, handheld computers, cell phone
game consoles etc.
• Some of the popular forms of memory cards are:
secure digital card, compact flash card, smart
media, memory stick etc.
SD Card: SD card is one of the more common types of
memory cards used with electronics. The SD
technology is used by over 400 brands of electronic
equipment and over 8000 different models, including
digital camera and cell phone

31. Introduction to input/output devices
• Devices that is used to feed data into
computer called.
• It sends data into the CPU or RAM.
• A digital computer can only understand
binary codes(codes of 0’s and 1’s)
• Therefore the data that human
understands must be converted into
binary codes.
• There are different types of input devices
some commonly used are: keyboard,
mouse, touch screen, light pen etc.

32. 1.keyboard
• Keyboard is the primary input device of
any computer system.
• It operates by converting key presses to
electronic signals in binary digital form.
• The key on computer keyboards are often
classified as follows:
 Alphanumeric keys: these include letters and
numbers
Punctuation keys: these include comma,
period, semicolon etc
Special keys: these include function keys,
control keys arrow keys, caps lock key etc.

33. 2.Mouse
• Mouse is an input device that controls the
movement of the cursor or pointer on a
display screen.
• It allows us to control the pointer in
graphical user interface.
• It is used to select menu commands,
move icons ,size window, start program,
close widows etc.
• There are three types of mice namely
mechanical , optomechanical and optical.

34. Types of mouse
Mechanical mouse: It has a rubber or metal ball on its underside
that can roll in all directions. Mechanical sensors (rods) within the
mouse detect the direction the ball is rolling and move the screen
pointer accordingly.
Optical mouse: It uses a laser light to detect the mouse’s
movement. Optical mouse have no mechanical moving parts and
no mouse pads are required. when the mouse is moved ,laser
rays hit the surface and provide the direction to the pointer on
the screen. This mouse respond more quickly and precisely than
mechanical and optomechanical mouse, but are little expensive.
Optomechanical mouse: An optomechanical mouse is same as
the mechanical mouse expect that the sensors used in it are
optical and not mechanical. The device is the combination of
optical and mechanical technologies, wherein, the ball is present
but the mouse movement is detected optically leading to more
accuracy .

35. 3.Touch panel
• A touch panel or touch screen is an
input device that lets users interact
with a computer by touching the
screen directly.
• It is an input and output device
normally layered on the top of an
electronic visual of an information
processing system.
• A user can give input or control the
information processing system by
touching the screen with special

36. light pen
• A light pen is also an input device for pointing
or selecting the objects in the screen .
• It is pen like device, which consists of photo
sensitive detector at its tip.
• It utilizes a light sensitive detector to select
objects on a display screen.
• It allows the user to point to displayed objects,
or draw on the screen ,in a similar way to
touch screen but with greater positional
accuracy
• It is generally used for drawing and in
computer aided design.

37. scanners
• Scanners are used to input images and
or text printed on a paper into
computer, allowing the computer to
read and or display the scanned object.
• A scanner works by digitizing an image
this means it divides printed into grid
of boxes and representing each box
with a combination of zeros and ones.
• The commonly used scanner are;
OCR,OMR,OBCR etc.

38. Types of optical scanners
• Optical Character Reader (OCR):The OCR devices are
used to scan special characters such as (alphabetic
and numeric character) printed on the paper and fed
into computer as input data.)
• Optical Bar-Code Reader(OBCR): Bar-code uses of bars
of varying thickness and spacing between them to
indicate the desired information.
• Optical Mark Reader(OMR): The optical mark reader is
a device the “Read” pencil marks on multiple choice
question answer sheets or other documents in similar
form.
• Magnetic ink character recognition: MICR is a character
recognition system that uses special ink and character.

39. Touch Pad
• Touchpad is an input device on laptops and
some keyboards to move a cursor with your
finger.
• It can be used in place of an external place
of an external mouse.
• Like most computer mice, the touchpad
also has two buttons below the touch
surface that allows you to left- click or right-
click .
• The pad contains several layers of material
• The top layer is the pad that you touch.
• Beneath layers contains horizontal and
vertical rows of electrodes that form a grid.

40. Output devices
• Any peripheral device that receive and
display output is called an output device.
• An output device is also defined as any
piece of computer hardware equipment
used to communicate the results of a
computer to the outside world.
• Output devices are responsible for
converting output in binary form to human
understandable form.
• Example of output devices are : printer,
plotter monitor, speaker .

41. Monitor
• It is called video display terminal or display screen.
• It is used to display information, program and application in a
computer.
• It is also called primary output device or standard output device.
• Pixel is the smallest unit of the monitor.
• Quality of monitor depends on resolution, dot pitch and color
depth.
• Dot pitch: space between pixels is called dot pitch. Finer the dot
pitch, better the quality of monitor will be.
• Color Depth: Number of bits used to represent the color
information of a pixel is called color depth. Higher the color depth,
better the quality of monitor will be.
• Resolution: Number of pixels in a row by number of pixels column
is called resolution of the monitor. Higher the resolution, better the
quality of display unit will be.
• Different type of monitor are: CRT monitor, LCD monitor , LED
monitor , and Plasma display panel.

42. CRT Monitor
• CRT stands for cathode-ray-tube.
• In CRT, beam of electrons(cathode rays)
emitted by an electron gun passes
through focusing and reflection systems
and its specified positions on the
phosphor-coated screen.
• The phosphor then emits a small spot of
light at each position contacted by the
electron beam to display information.
• To display the information continuously,
monitor needs to be refreshed
periodically.

43. LCD monitor
• LCDS are commonly used in PDA’s ,
calculators, laptops, and desktop
computers.
• These devices produce a picture by
passing polarized light from an
internal light source through a liquid
– crystal material.
• LCD monitors consumes less power
than CRT monitor but they are more
expensive.
• Viewing angle of LCD monitors is less

44. LED Monitor
• An LED (Light emitted Diode) display is a type
of that panel display that uses an array of
light-emitted diodes as pixels for a video
display.
• The actual difference between this and a
typical LCD monitors is the backlighting.
• LCD monitors use CCFL (Cold cathode
Fluorescent Lighting) instead of LED’s to
illuminate the screen.
• LED monitors are less expensive, Posses more
quality and have longer life than LCD
monitors.

45. Plasma Display Panel(PDP)
• A plasma display is a computer video display in
which each pixel on the screen is illuminated
by a tiny bit of plasma or charged gas.
• Plasma displays are thinner than cathode ray
tube displays and brighter than liquid crystal
displays.
• A plasma display is flat rather than slightly
curved as a CRT display is and therefore free of
distortion on the edges of the screen
• Unlike many LCD displays , a plasma display
offers a very wide viewing angle.
• It is a type of flat panel display common to
large TV displays 36 inches of larger.

46. Printers
• Printers is an external hardware device that
prints data on paper.
• It generates hard copy of the computer data.
• Printers are one of the most used peripherals
on computers and are commonly used to print
text, images etc.
• Print resolution is measured as the number of
dots per inch(dpi).
• Print speed is typically measured in pages per
minute(ppm).
• Currently different types of printers are in use.
• Some common type of printers are :impact
printer and non-impact printer.

47. 1.Impact printers
• The impact printer prints the
characters or images by striking print
hammer or wheel against inked
ribbon.
• characteristics of Impact Printers are
the following:
1. Very low consumable costs
2. Very noisy
3. Useful for bulk printing due to
low cost
• Impact printer includes dot-matrix

48. Dot-matrix printer
• Dot-matrix printer creates characters
by striking pins against an inked
ribbon; each pin makes a dot and
combination of dots form characters
and illustrations. Dot-matrix printers
are relatively expensive and do not
produce high quality output. Today,
Dot-matrix printers are rarely used or
found because of the low quality
print compared to other categories of
printers.

49. Line printer
• Line printer is high speed printers
capable of printing an entire line at
one time. A fast line printer can print
as many as 3000 lines per minute.
The disadvantages of line printers
are that they can not print graphics,
the print quality is low, and they are
very noisy.

50. Non-impact printers
• Non-impact printers print the
characters without using ribbon.
These printers print a complete page
at a time so they are also called as
Page Printers.
• These printers are of three types
 Ink-jet printers
Laser printer
Thermal printer

51. Ink-jet printer
Inkjet printers are non-impact character printers based
on a relatively new technology. They print characters by
spraying small drops of ink onto paper. Inkjet printers
produce high quality output with presentable features.
They make less noise because no hammering is done
and these have many styles of printing modes available.
Color printing is also possible. Some models of Inkjet
printers can produce multiple copies of printing also.
Advantages
High quality of printing
More reliable
Disadvantages
Expensive as cost per page is high
Slow as compared to laser printer

52. Laser printers
• Laser printers utilizes laser beam to produce
image on a drum. The light of the laser alters
the electrical charge on the drum whenever it
hits. The drum is then rolled through a
reservoir of toner. Finally, the toner is
transferred to the paper through a
combination of heat and pressure. Because
an entire page is transmitted to a drum
before the toner is applied, laser printers are
sometimes called page printers. Output
quality laser printer is better than ink-jet
printers and dot- matrix printers.

53. Thermal printer
Thermal printer produce a printed image by
selectively heating coated thermal paper
when the paper passes over the thermal
print head. The coating turns into
appropriate color in the areas where it is
heated, producing an image. The printer
sends an electric current to the heating
elements of the thermal head, which
generate heat. The heat activates the
thermo- sensitive coloring layer of the
thermo-sensitive paper, which changes color
where heated.

54. Difference between impact and
non-impact printer
Impact Printer Non- impact printer
1. It prints characters or Images
by striking print hammer or wheel
against an inked ribbon.
It prints characters and images
without striking the papers.
2. Its speed is slower . Its speed is faster.
3. Its printing quality is lower. Its printing quality is higher.
4. It generates noise during
printing.
It does not generate noise during
printing.
5. It uses inked ribbon for printing
.
It uses toner or cartridge for
painting.
6. Dot matrix is an impact printer. Laser printer is a non-impact
printer.
7. It is less expensive It is more expansive.

55. Plotters
• Plotter is a computer hardware device much
like a printer that is used for printing vector
graphics.
• Instead of toner, plotters use a pen, pencil,
marker, or another writing tool to draw
multiple, continuous lines onto paper rather
than series of dots like traditional printer.
• Plotters were the first type of printer that
could print with color and render graphics and
full-size engineering drawings.
• Plotters are much more expensive than
printers.
• They are most frequently used for CAE such as
CAD.