5. What is Computer
Definition:
A computer is an electronic device which takes
input from user, process it and gives output to
the user.
CPU
INPUT
OUT
PUT
USER
USER
7. Central Processing Unit:
The central processing unit (CPU) or processor, is the
unit which performs most of the processing inside a
computer. It processes all instructions received by
software running on the PC and by other hardware
components, and acts as a powerful calculator.
8. Central Processing Unit (CPU) consists of the
following features −
• CPU is considered as the brain of the computer.
• CPU performs all types of data processing
operations.
• It stores data, intermediate results, and
instructions (program).
• It controls the operation of all parts of the
computer.
9. CPU itself has following three components:
• Memory or Storage Unit
• Control Unit
• ALU(Arithmetic Logic Unit)
10. Memory or Storage Unit:
This unit can store instructions, data, and intermediate results. This unit
supplies information to other units of the computer when needed. It is
also known as internal storage unit or the main memory or the primary
storage or Random Access Memory (RAM).
Its size affects speed, power, and capability. Primary memory and
secondary memory are two types of memories in the computer. Functions
of the memory unit are −
• It stores all the data and the instructions required for processing.
• It stores intermediate results of processing.
• It stores the final results of processing before these results are released to
an output device.
• All inputs and outputs are transmitted through the main memory.
11. Control Unit:
This unit controls the operations of all parts of the computer but
does not carry out any actual data processing operations.
Functions of this unit are −
• It is responsible for controlling the transfer of data and instructions
among other units of a computer.
• It manages and coordinates all the units of the computer.
• It obtains the instructions from the memory, interprets them, and
directs the operation of the computer.
• It communicates with Input/output devices for transfer of data or
results from storage.
• It does not process or store data.
12. ALU (Arithmetic Logic Unit):
This unit consists of two subsections namely,
• Arithmetic Section
• Logic Section
Arithmetic Section
• Function of arithmetic section is to perform arithmetic operations
like addition, subtraction, multiplication, and division. All complex
operations are done by making repetitive use of the above
operations.
Logic Section
• Function of logic section is to perform logic operations such as
comparing, selecting and matching of data.
13. What are INPUT DEVICES ?
Devices are used to enter data and instructions into computer
memory from external world are called Input Devices.
Examples include:
• Keyboard
• Mouse
• Track ball
• Joystick
• Light pen
• Touch Screen
• Scanner
14. Input Unit
Input Unit perform three main functions:
• Receive data from user.
• Convert data into binary form [the language of 0 and 1 also
called the machine language. Machine language is the only
language, a computer can understand directly.
• Provide converted data to computer memory for processing.
15. What are OUTPUT DEVICES ?
Devices used to display results of processing to the user are
called Output Devices.
Examples include:
• Monitor
• Printer
• Plotter
• Speaker
• Projector
16. Output Unit
Output Unit perform the following functions:
• Receive results from memory.
• Convert data into human readable form.
• Display results to the user.
17. Components of computer
• Processor: It executes instructions from software and
hardware.
• Memory: It is the primary memory for data transfer between
the CPU and storage.
• Motherboard: It is the part that connects all other parts or
components of a computer.
• Storage Device: It permanently stores the data, e.g., hard
drive.
• Input Device: It allows you to communicate with the
computer or to input data, e.g., a keyboard.
• Output Device: It enables you to see the output, e.g.,
monitor.
18. Motherboard
• The motherboard serves as a single platform to connect all of
the parts of a computer together.
• It connects the CPU, memory, hard drives, optical drives,
video card, sound card, and other ports and expansion cards
directly or via cables.
• It can be considered as the backbone of a computer.
20. Motherboard
• Motherboard contains ports to connect all of the internal
components. It provides a single socket for CPU, whereas for
memory, normally one or more slots are available.
• Motherboards provide ports to attach the floppy drive, hard
drive, and optical drives via ribbon cables.
• Motherboard carries fans and a special port designed for
power supply.
21. Motherboard
• There is a peripheral card slot in front of the motherboard
using which video cards, sound cards, and other expansion
cards can be connected to the motherboard.
• On the left side, motherboards carry a number of ports to
connect the monitor, printer, mouse, keyboard, speaker, and
network cables.
22. Processor
• A processor or microprocessor is a small chip that resides
in computers and other electronic devices.
• Its basic job is to receive input and provide the
appropriate output.
• While this may seem like a simple task, modern processors
can handle trillions of calculations per second.
23. Processor
• The central processor of a computer is also known as the CPU,
or central processing unit.
• This processor handles all the basic system instructions, such
as processing mouse and keyboard input and
running applications.
• Each processor is constituted of one or more individual
processing units called cores.
24. Processor
• Each core processes instructions from a single computing task
at a certain speed.
• Modern CPUs often include multiple processing cores, which
work together to process instructions.
• While these cores are contained in one physical unit, they are
actually individual processors.
• Processors that include two cores are called dual-
core processors, while those with four cores are called quad-
core processors.
26. Main Memory
• Memory is the most essential element of a computing system
because without it computer can’t perform simple tasks.
• Computer memory is of two basic type –
1. Primary memory(RAM and ROM)
2. Secondary memory(hard drive, CD, etc.).
• Random Access Memory (RAM) is primary-volatile memory
and Read Only Memory (ROM) is primary-non-volatile
memory.
28. Main Memory
1. Random Access Memory (RAM) –
• It is also called as read write memory or the main memory or
the primary memory.
• The programs and data that the CPU requires during
execution of a program are stored in this memory.
• It is a volatile memory as the data loses when the power is
turned off.
• RAM is further classified into two types- SRAM (Static Random
Access Memory) and DRAM (Dynamic Random Access
Memory).
29. Main Memory
Types of RAM –
1. Static Random Access Memory (SRAM) :
• Data is stored in transistors and requires a constant power
flow.
• Because of the continuous power, SRAM doesn’t need to be
refreshed to remember the data being stored.
• SRAM is called static as no change or action i.e. refreshing is
not needed to keep the data perfect.
30. Main Memory
Types of RAM –
1. Static Random Access Memory (SRAM) :
• It is used in cache memories.
• Advantage: Low power consumption and faster access
speeds.
• Disadvantage: Less memory capacities and high costs of
manufacturing.
31. Main Memory
Types of RAM –
1. Static Random Access Memory (SRAM) :
• It is used in cache memories.
• Advantage: Low power consumption and faster access
speeds.
• Disadvantage: Less memory capacities and high costs of
manufacturing.
32. Main Memory
Types of RAM –
2. Dynamic Random Access Memory (DRAM) :
• Data is stored in capacitors.
• Capacitors that store data in DRAM gradually(slowly-slowly)
discharge energy, no energy means the data has been lost.
• So, a periodic refresh of power is required in order to
function.
33. Main Memory
Types of RAM –
2. Dynamic Random Access Memory (DRAM) :
• DRAM is called dynamic as constant change or action i.e.
refreshing is needed to keep the data intact(perfect).
• It is used to implement main memory.
• Advantage: Low costs of manufacturing and greater memory
capacities.
• Disadvantage: Slow access speed and high power
consumption.
35. Main Memory
2. Read Only Memory (ROM) –
• Stores important information essential to operate the system,
like the program essential to boot the computer.
• It is not volatile.
• Always retains its data.
• Used in embedded systems or where the programming needs
no change.
• Used in calculators and peripheral devices.
• ROM is further classified into 3 types- PROM, EPROM,
and EEPROM.
36. Main Memory
2. Read Only Memory (ROM) –
• Types of Read Only Memory (ROM) –
1. PROM (Programmable read-only memory) –
• It can be programmed by user.
• Once programmed, the data and instructions in it cannot be
changed.
37. Main Memory
2. Read Only Memory (ROM) –
• Types of Read Only Memory (ROM) –
2. EPROM (Erasable Programmable read only memory) –
• It can be reprogrammed.
• To erase data from it, expose it to ultra violet light.
• To reprogram it, erase all the previous data.
38. Main Memory
2. Read Only Memory (ROM) –
• Types of Read Only Memory (ROM) –
3. EEPROM (Electrically erasable programmable read only
memory) –
• The data can be erased by applying electric field, no need of
ultra violet light.
• We can erase only portions of the chip.
40. Cache Memory
• The data or contents of the main memory that are used
frequently by CPU are stored in the cache memory so that the
processor can easily access that data in a shorter time.
• Whenever the CPU needs to access memory, it first checks the
cache memory.
• If the data is not found in cache memory, then the CPU moves
into the main memory.
• Cache memory is placed between the CPU and the main
memory.
42. Cache Memory
The basic operation of a cache memory is as follows:
• When the CPU needs to access memory, the cache is
examined. If the word is found in the cache, it is read from the
fast memory.
• If the word addressed by the CPU is not found in the cache,
the main memory is accessed to read the word.
43. Cache Memory
• The performance of the cache memory is frequently
measured in terms of a quantity called hit ratio.
• When the CPU refers to memory and finds the word in cache,
it is said to produce a hit.
• If the word is not found in the cache, it is in main memory and
it counts as a miss.
• The ratio of the number of hits divided by the total CPU
references to memory (hits plus misses) is the hit ratio.
44. Hard Disk
• It is a rigid magnetic disc that is used to store data. It
permanently stores data and is located within a drive unit.
45. Hard Disk
• The hard disk is also known as a hard drive.
• It is a rigid magnetic disc that stores data permanently, as it is
a non-volatile storage device.
• The hard disk is located within a drive unit on the computer's
motherboard and comprises one or more platters packed in
an air-sealed casing.
• The data is written on the platters by moving a magnetic head
over the platters as they spin.
• The data stored on a computer's hard drive generally includes
the operating system, installed software, and the user's files
and programs, including pictures, music, videos, text
documents, etc.
46. Hard Disk
Components of Hard Disk :
• The main components of a hard drive include a head actuator,
read/write actuator arm, read/write head, platter, and
spindle.
• A circuit board, which is called the disk controller or interface
board, is present on the back of a hard drive. It allows the
hard drive to communicate with the computer.
47. Input Devices
• Input device is any electro-mechanical device that enables the user
to send data, information, or control signals to a computer.
• The Central Processing Unit (CPU) of a computer receives the input
and processes it to produce the output.
• The input may be text, number, graphics, sound, video etc.
• In general, any sensor that monitors or scans information from
the external world for the computer can be considered an input
device, whether or not the information is under the direct
control of a user.
48. Input Devices
Keyboard :
• The keyboard is a basic input device that is used to enter data
into a computer or any other electronic device by pressing
keys.
• It has different sets of keys for letters, numbers, characters,
and functions. Keyboards are connected to a computer
through USB or a Bluetooth device for wireless
communication.
• As the name implies, a keyboard is basically a board of keys.
• The keyboard is one of the primary input devices used with
a computer.
49. Input Devices
Keyboard :.
• The keyboard's design comes from the original typewriter
keyboards.
• This keyboard layout is known as the QWERTY design, which
gets its name from the first six letters across in the upper-left-
hand corner of the keyboard.
• Besides the QWETRY keyboard other layouts of keyboards are
also available like Dvorak keyboard and AZERTY keyboard.
• A keyboard includes the standard typewriter keys, several
specialized keys.
50. Input Devices
Keyboard :.
• Alphanumeric keys :
• These are key from a-z, 0-9 and space, used to input these
letters. Keyboards also have an extra numeric pad which can
be used to enter numbers or move the cursor and its mode
can be controlled by num lock key. By using numeric keys in
combination with Shift key, special characters like @, $, #, %,
& etc. can be input.
51. Input Devices
Keyboard :.
• Enter (Return) Key : In text applications, it ends a paragraph
or short line. In data applications, it signals the end of the
input for that field or line. After typing any command line, it
will be executed after pressing Enter key.
• Cursor Keys : There are various keys on keyboard to move the
cursor. The four arrow keys move the cursor on screen by one
character o line. Home and end Keys commonly used to move
the cursor to the left or right end of the current line. Page
Up/Page Down Keys used to move the cursor up and down a
page, screen or frame.
52. Input Devices
Keyboard :
• Function Keys : Used to call up a menu or perform a function
i.e. used as short cut keys. They are located in a row on the top
of the keyboard (F1 , F2, etc.). These can be used with the Shift,
Ctrl and Alt keys to extend the number of options.
•Backspace/ Delete Key : Used to delete the character.
Backspace key is used to delete the character at the left of the
cursor. Delete key deletes a character from current cursor
location.
•Modifier Keys : Ctrl, Alt and Shift keys are known as modifier
keys, because when used with other normal key they changes
its normal behavior. Generally these are used in shortcut keys.
53. Input Devices
• Types Of Keyboards:
• Membrane keyboards: Membrane keyboards are the most
commonly used with computers.
• They are designed so that all the keys are positioned above
rubber domes, which itself is placed above a 3-layer plastic
membrane that spreads over the entire keyboard.
• Whenever the user presses the key, a contact point at the top
of the rubber dome pushes the top layer through a hole in the
middle layer to contact the bottom layer, creating a short circuit
which generates the keystroke that is then sent to the computer.
54. Input Devices
• Types Of Keyboards:
• Mechanical keyboards:
• In these keyboards each key has its own switch system instead
of a common medium as in membrane keyboard.
• Normally a metal spring or such mechanism is used to control
the motion of key. It is costlier than membrane keyboard.
• It is appreciated by professional typists.
56. Input Devices
Mouse :
• The mouse is a hand-held input device which is used to move
cursor or pointer across the screen.
• It is designed to be used on a flat surface and generally has
left and right button and a scroll wheel between them.
• Laptop computers come with a touchpad that works as a
mouse.
• It lets you control the movement of cursor or pointer by
moving your finger over the touchpad.
• Some mouse comes with integrated features such as extra
buttons to perform different buttons.
57. Types of Mouse :
1. Mechanical Mouse:
• It has a system of a ball and several rollers to track its
movement. It is a corded type of mouse.
• A mechanical mouse can be used for high performance.
• The drawback is that they tend to get dust into the mechanics
and thus require regular cleaning.
58. Types of Mouse :
1. Mechanical Mouse:
• A mechanical mouse uses a ball and two rollers to sense the
motion.
• A disk having holes on its periphery is attached to each roller.
• On either side of the disk there is an infrared LED and .an
infrared sensor.
• The holes in the disk break the beam of light coming from the
LED so that the infrared sensor senses pulses of light.
• As user moves the mouse on a. mouse pad, movement of ball
causes rotation in roller, which in turn rotates the disks
accordingly.
• Signal from LED reach to sensor, which send them to the
onboard processor of mouse.
• It converts the signals into binary data and sends it to computer.
59. Types of Mouse :
2. Optical Mouse:
• An optical mouse uses optical electronics to track its
movement.
• It is more reliable than a mechanical mouse and also requires
less maintenance.
• However, its performance is affected by the surface on which
it is operated.
• Plain non-glossy mouse mat should be used for best results.
• The rough surface may cause problems for the optical
recognition system, and the glossy surface may reflect the
light wrongly and thus may cause tracking issues.
61. Types of Mouse :
2. Optical Mouse:
• A LED (Light Emitting. Diode) and a photo sensor do the same
work in the optical mouse, which are positioned at the base of
mouse.
• When mouse is moved on any surface, the light emitted by LED is
reflected by that surface which is sensed by the sensor, which send
signals to onboard processor.
• The optical mouse is more convenient than mechanical mouse
as it need not any special mouse pad and can be run on any surface.
• There is no physical contact with the surface, hence the life of
optical mouse is more and less maintenance.
62. Trackball
• Trackball is a pointing device like a mouse upside down.
• It is a stationary device that contains a movable ball rotated
with the thumb, fingers or palm to move the pointer.
• There are usually one to three buttons next to the ball, which
are used just like mouse buttons.
• The advantage of trackballs over mouse is that the trackball is
stationary so it does not require much space to use it.
• In addition, a trackball can be placed on any type of surface.
• For both these reasons, trackballs are popular pointing devices
for portable computers like laptops.
63. Joystick
• A pointing device used to move an object on screen in any
direction.
• It employs a vertical rod mounted on a base with one or two
buttons.
• With a joystick, the pointer continues moving in the direction
the joystick is pointing.
• To stop the pointer, the joystick must return to its upright
position.
• Most joysticks include two or more buttons called triggers,
which works like the mouse buttons.
• Joysticks are used extensively in video games and in some
CAD systems.
64. Digitizing Tablet
• A Digitizing tablet is a computer input device that allows to input
hand-draw images and graphics, similar to the way we draws
images with a pencil and paper.
• It also called as graphics tablet.
• A Digitizing tablet consists of a flat surface upon which the user
may draw an image using either a pen-like drawing apparatus
called as stylus or a cursor also called as puck.
• Stylus or pen looks like a simple ballpoint pen but uses an
electronic head instead of ink.
• Cursor or puck looks like a mouse, but it may have as many as 16
buttons.
• The tablet contains electronics that enable it to detect movement
of the cursor or pen and translate the movements into digital
signals that it sends to the computer.
• The image generally does not appear on the tablet itself but, it is
displayed on the computer monitor.
65. Scanners
• Scanner is an optical device that reads a printed text or image
and converts it into a digital graphics image for the computer.
• The scanner does not recognize or differentiate in any manner
the content of the material it is scanning.
• Everything is converted into a bitmapped image, which is a pattern
of dots.
• A scanner works by digitizing an image.
• The scanner divide the image into a grid of dots and representing
each dot with either a zero or a one.
• The resulting matrix of bits, called a bit map, can then be stored in
a file, displayed o a screen, and manipulated by programs.
• Optical scanners do not distinguish text from graphics they
represent all images as bit maps
66. Scanners
• Therefore, scanned text can not be used directly for editing.
• Scanners may be divided mainly into three types : Flatbed,
Handheld and Drum Scanner.
(1) Flatbed scanner :
• A flatbed scanner is that provides a flat, glass surface to hold
pages of paper, books and other objects for scanning.
• The scan head is moved under the glass across the page to
scan the image.
67. Scanners
(2) Handheld Scanner :
• A handheld scanner is that moved across the image to be
scanned by hand.
• Handheld scanners are small and less expensive, but it relies
on accuracy of the user to move the unit across the image.
• Trays are available that keep the scanner moving in a straight
line.
68. Scanners
(3) Drum scanner :
• Drum scanner is a type of scanner on which original paper is
attached to the outside of a spinning glass drum.
• The image is scanned by photo multiplier tube (PMT) and is
saved to a disk file.
• This type of scanner gives the best quality result.
• These are very costly.
69. Digital cameras
• A digital camera (popularly known as digicam) is a camera that
records images in digital form.
• Unlike traditional film cameras that record a light image on
film, digital cameras use binary numbers for storage of an
image on a flash memory card or optical disk.
• Digital cameras can also be connected to the computer to
input images directly.
• To connect with a computer a USB cable or wireless media
can be used.
• As with all digital devices, there is a fixed, maximum
resolution and number of colors that can be represented.
70. Digital cameras
• There are three main advantages of digital cameras:
1. The first is ability to preview the final image, so only right
pictures are going to be saved or printed.
2. Even a single picture can be taken and Printed without
waiting to develop an entire roll of film or wasting the whole
roll.
3. The third is digital film is reusable since images can be erased
from media.
71. Optical Character Recognition
• Optical Character Recognition, or OCR, is a technology that can
convert different types of documents, such as scanned paper
documents, PDF files or images captured by a digital camera
into editable text.
• When a text document is scanned into the computer through
OCR, it is turned into a bitmap, which is a picture of the text.
• OCR software analyzes the light and dark areas of the Bitmap
in order to identify each alphabetic letter and digit.
• When it recognizes a character, it converts ASCII text.
• Advanced OCR systems can recognize hand writing.
72. Optical Character Recognition
• All OCR systems include an optical scanner for reading text, and
sophisticated software for analyzing images.
• OCR is already being used widely in many professions, where
searches that once required hours or days in books can now be
accomplished in a few seconds by converting them into digital
format.
73. Optical Mark Recognition
• OMR is acronym for Optical Mark Recognition.
• OMR technology scans a printed or marked form and reads
at predefined positions and records, where marks are made
on the form.
• This technology is useful for applications in which large
numbersof hand-filled forms need to be processed quickly
and with great accuracy, such as surveys, questionnaires
and ballots.
• A common OMR application is the use of bubble answer
sheets for multiple-choice tests.
• The student marks the answer on the answer sheet by filling
in the corresponding circle by HB pencil, and the answer sheet
is fed through an optical mark reader.
74. Output Devices
• The result of any process performed by computer on input is
called output.
• The CPU output is send to the output devices.
• An output device is that device by which a computer transfers
its information to the outside world.
• In general an output device is a machine that translates
machine-readable data into human-readable information.
75. Display Devices
• A computer display, technically termed as visual display unit is
an output device that presents the information from the CPU
on the screen.
• A cable connects the display unit to a video adaptor or video
card on the motherboard of the computer.
• The CPU sends instruction to the video adaptor to display
information on the screen.
76. Display Devices
• The video adaptor converts the instructions into a set of
corresponding signals and sends to the display unit.
•
• Display unit contains a circuitry that generates the picture on
the screen from the set of signals.
• There are many types of display devices available like CRT
monitors, LCD Monitors, LED Monitors, Projectors etc
77. Characteristics of Display Units
(1) Resolution
• Resolution is expressed in terms of the number of pixels
appearing on the screen.
• A pixel is smallest part or dot of computer screen.
• The more is the number of pixels, the sharper the image.
• Resolution is represented by the number of pixels in the
horizontal and vertical lines.
• For example a screen with 800 x 600 resolution will have 800
pixels in a horizontal line and 600 pixels in a vertical line.
• Besides this, quality of picture also depends upon number of
colors that can be displayed by the screen. A screen can
display from 16 to millions of colors.
78. Characteristics of Display Units
(2) Dot Pitch
• Dot pitch expresses the distance between the pixels on a
monitor screen.
• Closer dots or lower dot pitch number generates brighter
image for example 0.28 dot pitch provide brighter image
than 0.31 dot pitch.
79. Characteristics of Display Units
(3) Refresh Rate
• Rate at which the screen image is redrawn.
• Higher refresh rates results in less flickering on the screen.
(4) Size
• Size of the monitor is measured diagonally from one corner
of the screen to another.
• Generally measured in inches (14,15 , 17 ,19 etc.).
• Price of monitors increases with the size.
80. Types of Monitors
(A) CRT Monitors
• Monitors are one of the most important components of a
computer system.
• The main component of a monitor is the cathode ray tube
(CRT).
• Images created by passing an electron beam over the colored
phosphors on the front of the tube which is illuminated
according to intensity of beam.
• A monitor is connected to the computer through a video card
or graphic adapter card, which transmits graphical output
signals from computer to monitor.
81. Types of Monitors
(B) LCD Monitors
• LCD Stands for Liquid Crystal Display.
• LCDs are super-thin displays that are used in laptop computer
screens and flat panel monitors.
• Smaller LCDs are used in handheld TVs, PDAs, mobiles and
portable video game devices.
82. Types of Monitors
(B) LCD Monitors
• The image on an LCD screen is created by placing a thin layer
of special electrically active substance between two
electrodes.
• The color of this substance can be changed by increasing or
reducing the electrical current.
• Since LCD screens are based on the principle of blocking light
rather than emitting it, they use much less power than
standard CRT monitors but these are costlier than CRT
monitor.
83. Types of Monitors
(C) LED Monitors
• An LED (Light Emitting Diode) monitor or LED display is a flat
panel computer monitor.
• An LED is a semiconductor device that emits visible light when
an electric current passes through it.
• LED monitors uses an array of light emitting diodes as pixels.
• It has a very low thickness and very light weight.
• Typically LED monitors are less expensive and more reliable.
• They consume much less power as compare to CRT or LCD
monitors.
• LED monitors provide higher contrast ratio.
84. Types of Monitors
(D) Multimedia Projector
• A projector projects images onto a wall or projection screen.
• Projectors are typically used to increase the image size for
viewing by audiences.
• A multimedia projector processes a specific video signal and
projects a corresponding image on a large screen using a lens
system.
• Projectors incorporate the use of a very bright light to display
the image.
85. Types of Monitors
(D) Multimedia Projector
• Multimedia projectors are capable of numerous display
resolutions.
• The quality of a projector is depend on its resolution and its
light output.
• Light output is normally measured in Lumens which is the
brightness of the light.
• This brightness will determine the size of the image that is
projected and the distance of the projector from the screen.
86. Sound Card
• A sound card is a card inside the computer that enables the
computer to input, manipulate and output sounds.
• Sound cards enable the computer to output the sound
through speakers connected to the computer and to record
the sound input from a microphone connected to the
computer.
• It also allows manipulating sound stored on secondary
storage devices.
• The sound card is usually a separate circuit board that is
plugged into the motherboard.
• In modern computer systems sound card is normally built
into the motherboards.
87. Sound Card
• A sound card is able to convert analog sound of microphone
or any other sound input device to digital signal using analog
to digital converter (ADC).
• It can also convert digital sound signals into analog signal for
speaker, recorder or other sound output device through a
digital to analog converter (DAC).
• Typical uses of sound cards include providing the audio
component for multimedia applications such as music
composition, editing video or audio, presentation/education,
games and entertainment.
88. Speakers
• A speaker is an output device of computer for sound.
• A speaker is connected with computer through a soundcard.
• Basic function of speaker is to convert electrical signals
generated by sound card into sounds, which is loud enough
to be heard at a distance.
• The quality of sound produced is depend upon both speaker
and sound card.
• A speaker may require external power supply to amplify the
sound.
• Today speakers are available as set of two or more speakers.
• High quality sound system may contain multiple speakers
with subwoofers for enhanced sound effect.
89. Printers
• In computers, a printer is a device that accepts text and
graphic output from a computer and transfers the information
to paper.
• Printers vary in size, speed and cost.
• Printers are mainly differentiated on the basis of following
characteristics :
(1) Quality of type : The output produced by printers is said to
be either letter quality, near letter quality or draft quality.
(2) Speed : Measured in characters per second (cps) or pages
per minute (ppm), the speed of printers varies widely.
90. Printers
(3) Impact or non-impact :
Impact printers include all printers that work by striking an
ink ribbon.
Non-impact printers include laser printers and ink-jet
printers. Impact printers usually make much noise.
(4) Graphics : Some printers can print only text. Other printers
can print both text and graphics.
(5) Fonts : Some printers, notably dot-matrix printers, are limited
to one or a few fonts.
91. Daisy-Wheel Printer
• Daisy wheel printer is an impact printer that produces letter-
quality type.
• The daisy wheel is a disk made of plastic or metal on which
characters are attached along the outer edge.
• To print a character, the printer rotates the disk until the desired
letter is facing the paper.
• Then a hammer strikes the disk, forcing the character to hit an ink
ribbon, leaving an impression of the character on the paper.
• You can change the daisy wheel to print different fonts.
• Daisy-wheel printers cannot print graphics, and in general they are
noisy and slow, printing from 10 to 75 characters per second.
• Daisy-wheel printers have become obsolete now.
92. Dot Matrix Printer
• The dot matrix printer is an impact printer.
• It uses one or two columns of dot hammers that are moved
across the paper.
• The hammers hit the ribbon into the paper, which causes the
ink to be deposited.
• The more hammers, the higher the resolution of printing.
• Dot matrix printers vary in two important characteristics one
is speed and second is print quality.
• The speed can vary from about 50 to over 500 cps.
93. Dot Matrix Printer
• Most dot-matrix printers offer different speeds depending on
the quality of print desired.
• Print quality determined by the number of pins present on
the head.
• It can vary from 9 to 24.
• The best dot-matrix printers (24 pins) can produce near letter-
quality type.
• A dot-matrix printer can use tractor-fed or friction rollers to
feed paper into the printer.
• Tractor feeds either push paper into the printer or pull paper
out of the printer to move paper.
• In a printer using friction rollers, the feed mechanism usually
only pushes the paper into the printer.
94. Line Printer
• The line printer is a high-speed impact printer in which one
entire line is printed at a time.
• Line printers are common in the corporate environment
where they are used with mainframe computers,
minicomputers and networked systems.
• 80 column, 132 column and 160 column (one character per
column) variants are common.
• Example of line printer are drum and chain printers.
• Line printers are fast and less expensive.
• Line printers have print speeds of 600 to 1200 lines-per-
minute (approximately 10 to 20 pages per minute).
95. Inkjet Printer
• Inkjet printers are called so, because they print by spraying
ionized ink on the sheet of paper to print text or image in
form of tiny dots.
• The dots are extremely small usually between 50 and 60
microns in diameter and even tinier than the diameter of a
human hair.
• Ink is filled in cartridges that may be separate for color and
black printing.
• Magnetized plates in the ink's path direct the ink dots on the
paper in the desired shapes.
96. Inkjet Printer
• Ink-jet printers are capable of producing high quality print.
• It is a color printer.
• It may have resolution from 300 dpi (dots per inch) to 1440
dpi or more.
• Print speed of inkjet printer may vary from 3 to 4ppm (page
per minute) in color and 12 to 14ppm in monochrome
depending upon quality of printing required.
• An inkjet printer needs a good quality paper for good quality
printing.
• If quality of paper is not appropriate, then dots may form
irregular shapes resulting in a bad print out.
97. Laser Printer
• A laser printer uses a laser beam to produce print out.
• A laser beam creates an image on a electrostatic drum.
• The light of the laser alters the electrical charge on the drum
wherever it hits.
• The drum is then rolled through a container of toner (ink).
• The charged portion of the drum picks toner from toner
reservoir.
• Finally, the drum with toner is rolled over the paper and by
using a combination of heat and pressure image or text is
fixed on paper.
98. Laser Printer
• This is also the way in which photocopy machines work.
• Because an entire page is transmitted to the drum before the
toner is applied, laser printers are sometimes called page
printers.
• One of the chief characteristics of laser printers is their
resolution measured in dots per inch (DPI).
• The available resolutions range from 300 DPI at the low end to
1,200 DPI at the high end.
• The speed of laser printers ranges from about 4 to 20ppm
(pages per minute).
99. Plotter
• A plotter is a vector graphic printing device.
• Plotters print their output by moving a pen or pencil across
the surface of a piece of paper.
• Unlike a regular printer, the plotter can draw continuous
point-to-point lines.
• This means that plotters can be used only to print line art.
• A plotter uses one or more pens that can be raised, lowered
and moved over the printing media.
• The plotter was the first computer output device that could
print graphics as well as accommodate full-size engineering
and architectural drawings.
• Using different colored pens, it was also able to print in color.
100. Plotter
• There are a number of different types of plotters.
Drum Plotter
• A drum plotter draws on paper wrapped around a drum,
which turns to produce one direction of the plot, while the
pens move to provide the other direction.
Flatbed Plotter
• A flatbed plotter draws on paper placed on a flat surface.
101. Plotter
• An electrostatic plotter draws on negatively charged paper
with positively charged toner like laser printer.
• Now a day inkjet plotters are very common for color plotting.
• Plotters can also be used for vinyl sign cutting for professional
posters and signboards.
• For this a very sharp cutter is used in place of pens.
