Chapter 2
 The
hardware and software is used as unit to
process data is called computer system.
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Hardware
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Input Devices
CPU
Output Devices
Storage
Software
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A set of instructions given to computer to solve a
problem is called software.
Software is also called program
Computer works according to the instructions written
in software
 Input
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devices
The data or instruction given to the computer is
called input.
A hardware component used to enter data and
instruction into computer is called input device
 Output
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Devices
The data processed into useful information is
called output.
A hardware component used to display
information to the user is called output devices.
 System
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Unit
System unit is a box that contains different
electronics components of a computer system.
The electronics components in the system unit
are connected to the motherboard.
Important components of system unit are CPU
and memory
 Storage
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The hardware components used to store data,
instruction and information permanently are
called storage devices.
Examples: Hard Disk, floppy Disk, CD, DVD, etc
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The data or instruction given to the computer is
called input.
A hardware component used to enter data and
instruction into computer is called input device
Types of input Devices
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Keyboard
Mouse
Trackball
Touchpad/Track pad
Pointing Stick
Graphic Tablet
Touch Screen
Digital Scanner
Digital Camera
Joystick
 Hardware
components that are used to
receive information from the computer are
called output devices.
 Output devices take information from the
computer and convert it in a form that is
understandable by users.
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Printers
Plotter
Display devices
Speaker& Headsets
Data Projrctors
 Printer
is an output device that prints
characters, symbols and graphics on paper.
 Printed output is called hardcopy.
 There are two types of printers.
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Impact Printers
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Dot Matrix Printers
Daisy wheel printers
Line Printers
Non-Printers
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Laser Printer
Inkjet Printer
 Impact
printer works like a typewriter.
 Prints characters or images by striking print
hammer or set of pins against an inked
ribbon.
 Ink is pressed from ribbon on the paper to
produce the output.
 Impact printers are used where low-cost
printing is required.
 Produces
printed images when tiny pins on a
print head strike an inked ribbon.
 When ribbon presses against the paper it
creates dot that form characters and
graphics.
 Contains 9 to 24 pins.
 Higher number of pins creates more dots that
produce high quality image.
 Speed of most dot-matrix printer ranges from
350 to 1100 characters per second.
 It
uses a print wheel. Print wheel is called
daisy wheel.
 Each petal of daisy wheel contains characters
 A motor rotates the wheel.
 A hammer strikes a petal against the ribbon
when the desired character reaches the
position on the paper.
 This prints the character on the paper.
 Slower than dot matrix printer but better in
quality
 Line
printer is a fast impact printer.
 It can print multiple characters on the same
line at a time.
 Its speed is measured in line per minute.
 Speed range of line printer is from 300LPM to
2400LPM
 Faster than dot matrix and daisy wheel.
 More noisy and provide limited font
capability.
 Example:Band printer and chain printer
A
non impact printer prints characters and
graphics on paper without striking paper.
 The characters are printed on paper with
some mean such as laser
 Some printers use spray in while other use
heat and pressure to create images.
 These printers are faster than impact printer.
 More costly than impact printers.
 Produce no noise during printing
 Print quality is better than impact printers
 Light
Amplification by stimulated emission of
radiation.
 Similar to a photocopying machine.
 Uses laser beams to burn special powder on
page to create a permanent image.
 Prints a complete page at a time
 Typical laser printer provides a resolution 0f
1200 DPI or more.
 Produces very high quality prints.
 Printing speed of laser printer ranges from 12
to 45 ppm
 It
prints characters and graphics by spraying
tiny drops of liquid ink on paper.
 These printers can produce quality text and
graphics in both black and white and color.
 Typical inkjet printer provides resolution of
600DPI or more.
 Slower than laser printer.
 Printers can print from 10 to 35 ppm.
 Inexpensive than laser printer
 Plotter
is an output devices that is used to
produce image quality graphics in variety of
colors.
 Plotters are used to create maps,
architectural drawings, graphs and charts.
 A plotter works by drawing lines on paper
using pens held in a mechanical arm.
Monitor is most common output device.
 The output displayed by monitor is called soft
copy.
 Looks like a television and displays text and
graphics.
 Different display screen can be distinguished on
the following features.
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Size
Color
Resolution
Refresh rate
Dot Pitch
Display Adapter
 Cathode
Ray Tube
 It can display text and graphics
 It used CRT that creates an image by an
electronic beam.
 CRT consists of one or more guns that fire a
beam of electrons inside the screen.
 The screen is coated with very tiny phosphor
dots from inside.
 The beam of electrons repeatedly falls on
the surface of screen.
 CRT in color monitor consists of three guns
RGB
 Laptop
PCs use flat panel monitors
 These monitor take less space.
 Flat panel monitor use a variety of
technologies
 Common technology is Liquid Crystal display
 LCD monitor use much less power than CRT.
 These are available in different sizes such as
15, 17, 19, 21, 32 and so on.
A
type of output produced in the form of
sound, voice or music is known as audio
output.
 Speakers and headsets are two commonly
used audio outputs.
 Many personal computers have internal
speaker.
 Headsets are also used to produce audio
output
CPU is the brain of Computer
 It is the most important component of a
computer
 It is also called processor
 A computer cannot work without CPU
 CPU is located of Mother Board
 Performs operations on data according to the
given instructions
 It can performs arithmetic and logical operations
 It executes and controls the computer hardware
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ALU(Arithmetic and Logic unit)
Performs basic arithmetic functions such as addition
subtraction multiplication and division
 Logic unit perform logical operations like comparing
two data items to find which is greater
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CU(Control Unit)
It generates signal to direct the entire computer
system
 It controls and coordinates all activities of computer
system.
 It does not executes program instructions
 Control unit communicates with arithmetic and
logical unit and other parts
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A
small high speed memory inside CPU
 CPU contains number of registers
 Registers are used to store information being
processed.
 Temporary storage area of instruction or data
 Temporary results during processing are also
stored in registers
 Each registers has a predefined function
 Data
in digital computers is represented as a
collection of bits.
 The smallest unit of data that can be used by
computer is called bit.
 A set of 8bit is called byte.
 One byte is required to store one character.
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Different types of memories are random access
memory and read-only memory
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RAM(Random Access Memory)
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It is also called Main Memory or Direct Access Memory
Each individual byte in the entire memory is directly
accessible.
Program must be loaded into RAM before execution
RAM is Volatile
ROM(Read Only Memory)
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Instructions in ROM prepare the computer for use.
Contents of ROM can only be read but cannot be changed
or deleted.
It stores data and instructions permanently
ROM is NON-Volatile
 DRAM
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Dynamic Random Access Memory
It is a type of memory that is used in most
computers
Least Expensive kind of memory.
It requires an electric current to maintain its
electrical state.
Electrical charge of DRAM decreases with time
that may result in loss of data.
DRAM is recharged or refreshed again and again
to maintain data.
Processor cannot access data of DRAM when its
being refreshed.
 Static
Random Access Memory
 It can store its value without any need to
refresh the data.
 Expensive type of memory
 CPU does not wait to access data so it is
faster.
 It utilizes more power than DRAM
 It is normally used to built faster cache
memory.
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PROM
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EPROM
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Programmable Read-only Memory
This form of ROM is initially blank
Manufacturer can write data on it using special device
The user can write data and instruction only once
If there is an error chip becomes unusable
Erasable Programmable Read Only Memory
Program and data written on it can be erased using
ultraviolet rays.
EEPROM
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Electronically erasable Programmable ROM
User can erase and write instruction using electrical
devices
Contents can be modified easily
 Cache
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Memory
Designed to speed up the transfer of data and
instructions.
It is located inside or close CPU.
Faster than RAM.
Data and instruction that are most recently or
frequently used by CPU
Data and instructions are retrieved from RAM
when CPU uses them for first time.