2. chapter 2: Input-Output in Computer.ppt

Introduction to Computers
Chapter No 2
I/O Devices and Peripherials
I/O Devices and Peripherials
Compiled By:Akhter Jahangir
Akhter_jahangir@yahoo.com

ITC - Chapter 2 I/O Devices and Peripherials 2
About the Course
 Text Book:
 Computer, Communications and Information.
By Sarah Hutchinson and Stacey Sawyer.
 Reference Book:
 Living With Computers
By Patrick Mckeown.

What Computers Do ?
Four basic functions
of computers
include:
 Receive input
 Process
information
 Produce output
 Store information

Input and Output Hardware
 Input Hardware
Consists of devices that translate data into a
form the computer can process.
 Output Hardware
Consists of devices that translate information
processed by the computer into the form that
humans can understand

Input Devices
 Computers accept information from the
outside world.
 The keyboard is the most common input
device.
 Pointing devices like the mouse also
receive input.

Process Information
 The processor, or central processing
unit (CPU), processes information, and
performs all the necessary arithmetic
calculations.
 CPU is like the “brain” of the computer.

Output Devices
 Computers produce information and
send it to the outside world.
 A video monitor is a common output device.
 Printers also produce output.

Store Information
 Memory and storage devices are used to
store information.
 Primary storage is the computer’s main
memory.
 Secondary storage uses disks or other
media.
Primary storage Secondary storage

Computer’s Core: The CPU and
Memory
 The transformations are
performed by the CPU -
the central processing
unit or processor.
 The microprocessor,
which is a silicon chip, is
located on the
motherboard.

 When you purchase a computer, the
selection of the CPU is a very important
choice. There are two factors that are
very important to computer users are:
 Compatibility
 Speed
Computer’s Core: The CPU and
Memory

Compatibility
 Not all software is compatible with any
given CPU. Each computer has a unique
instruction set - a vocabulary of
instructions the processor can execute.
 New microprocessors can usually run
older software, but new software is not
usually compatible with old
microprocessors.

Speed
 The computer’s speed is measured by the
speed of its internal clock - a device to
synchronize(match) the electric pulses.
 Speed is measured in units called megahertz
(mHz).

Primary Storage: The Computer’s
Memory
RAM ( Random Access Memory):
 RAM is the most common type of primary
storage, or computer memory.
 used to store program instructions and
data temporarily
 unique addresses and can store in any
location
 can quickly retrieve information
 will not remain if power goes off (volatile).

 ROM
( Read-Only Memory):
 information is stored
permanently on a
chip.
 contains startup
instructions and other
permanent data.
Primary Storage: The Computer’s
Memory

 Information travels between
components through groups of wires
called Buses.
Buses, Ports, and Peripherals

 Peripherals are external devices for
receiving input or producing output.
 Example (keyboard, monitor, and mouse).
 Communicate with other parts of the
system.

 Ports provide attachment and
communication with external devices by
means of:

Slots ( For internal attachments )

Ports ( For external attachments )

The Keyboard
 A standard computer keyboard has about
100 keys.
 Most keyboards use the QWERTY layout,
named for the first six keys in the top row
of letters.

 Do you know where these keys are located
on the keyboard and how to use them?
 Letters, Numbers, Cursor Keys, Delete
Key, Enter (Return) Key, and Function Keys
The Omnipresent Keyboard

 Most keyboards have keys arranged in five
groups:
 Alphanumeric keys
 Numeric keypad
 Function keys
 Modifier keys

Cursor-movement keys
Standard Keyboard Layout

Standard Keyboard Layout

Working of Keyboard

Mouse Joystick
Graphics Tablet
Touch Screen
Pointing Devices

Mouse
 The mouse is a pointing
device. You use it to
move a graphical
pointer on the screen.
 The mouse can be used
to issue commands,
draw, and perform
other types of input
tasks.

 Using the mouse involves five techniques:

Pointing;

Move the mouse to move the on-screen pointer.

Clicking

Press and release the left mouse button once.

Right-clicking

Press and release the right mouse button.

Double-clicking

Press and release the left mouse button twice.

Dragging

Hold down the left mouse button as you move the
pointer.
Mouse Techniques

Other Pointing Devices
 Trackballs:
 A trackball is like a mouse turned upside-
down. Use your thumb to move the
exposed ball and your fingers to press the
buttons.

Touchpads or Trackpads
 A touchpad is a touch-sensitive pad that
provides the same functionality as a
mouse.

To use a touchpad, you glide (slides) your
finger across its surface.

Touchpads provide a set of buttons that
function like mouse buttons.

Joystick
 It is also a pointing device.
 It consists of a vertical
handle like a gearshift
lever mounted on a base
with one or two buttons.
 They are primarily used for
playing games.
• Joysticks are popular for
flight simulator and driving
games.

Alternative Input Devices
 Light Pens
 Pen-based Systems
 Touch Screens
 Digitizing Tablets

Pen-based System
 With a pen-based system, you use an
electronic pen to write on the screen and
choose commands.
 Pens are common input devices for
handheld computers, like “personal
digital assistants (PDAs).”
 Pens are handy for making notes or
selecting commands, not for inputting a
lot of text.

Pen-based System
 The user can
point, tap, draw
and write on the
computer’s screen
with a pen

Touch Screens
 Touch-screen systems accept input
directly through the monitor.
 Touch screens use sensors to detect the
touch of a finger.
 They are useful where environmental
conditions prohibit the use of a keyboard
or mouse.
 Touch-screen systems are useful for
selecting options from menus.

Touch Screens

Digitizing Tablets
 An input device that enables you to enter
drawings and sketches into a computer.
 A digitizing tablet consists of an electronic
tablet and a cursor or pen.
 A cursor (also called a puck ) is similar to a
mouse, except that it has a window with
cross hairs for pinpoint placement, and it can
have as many as 16 buttons.
 A pen (also called a stylus) looks like a simple
ballpoint pen but uses an electronic head
instead of ink.

 A modem:
 Converts the digital stream of information
from a computer to an analog stream in
order to send a message on the telephone
network
Communication á la Modem

 A modem:
 Converts the analog stream of information
received over the telephone network into
the digital form that the computer
understands
Communication á la Modem

Terminal
Modem
Modem
Analog
signals
Phone line
Digital
signals
Digital
signals
Computer
 The word modem comes from the terms
modulation(carry) and demodulation
How a Modem Works
Modulation
Demodulation

Screen Output
 Video Monitor
 Also called Video Display Terminal (VDT)
 Image exists in video memory—VRAM

Monitor size is measured diagonally across the
screen

 Images are made up of dots called Pixels
for picture elements

The number of pixels affects the resolution
of the monitor

The higher the resolution, the better the
image quality
Pixels

CRT ( Cathode Ray Tube )LCD ( Liquid Crystal Display )
Classes of Monitors

 A CRT is a television-style monitor
 Its features include:
 Clear image
 Quick response time
 Low cost
 Very popular
CRT ( Cathode Ray Tube )

 LCDs comprise flat-panel monitors
 Features of flat-panel monitors include:
 Lighter weight
 More compact
 More expensive
 Dominate the portable
computer market
LCD (Liquid Crystal Display)

CRT Monitors
 In CRT monitors, electrons are fired at
phosphor dots on the screen.
 The dots are grouped into pixels, which
glow when struck by electrons.
 In color CRTs, each pixel contains a red,
green, and blue dot. These glow at
varying intensities to produce color
images.

CRT Monitors

Flat-Panel Displays Monitors
 Most flat-panel monitors use liquid crystal
display (LCD) technology.
 Passive matrix LCD uses a transistor for
each row and column of pixels.
 Active matrix LCD uses a transistor for
each pixel on the screen.
 Thin-film transistor displays use multiple
transistors for each pixel.

Factors affecting Screen Clarity
 Resolution
 Refresh rate
 Dot pitch

Resolution
 Resolution is the number of pixels on the
screen, expressed as a matrix. Example
such as 600x800.
 A 17" monitor offers resolutions from
640x480 up to 1280x1024.
 The Video Graphics Array (VGA)
standard is 640x480. Super VGA (SVGA)
monitors provide resolutions of 800x600,
1024x768 or higher.
 Resolution (image sharpness) is important.

Refresh Rate
 Refresh rate is the number of times each
second that the electron guns scan the
screen's pixels.
 Refresh rate is measured in Hertz (Hz), or
cycles per second.
 Look for a refresh rate of 72 Hz or higher.
A slower rate may cause eyestrain.

Fast scanning = Quick refresh (less flicker)
Refresh Rate

Dot Pitch
 Dot pitch is the distance between the
phosphor dots that make up a single
pixel.
 In color monitors, three dots (red, green,
and blue) comprise each pixel.
 Look for a dot pitch no greater than .31
millimeter.

Dot Pitch
R + B
B + G
R + G
R + B + G
Phosphor Dot Color Mixing

Video Controllers
 The video controller is an interface between
the monitor and the CPU.
 The video controller determines many
aspects of a monitor's performance, such as
resolution or the number of colors displayed.
 The video controller contains its own on-
board processor and memory, called video
RAM (VRAM).
 Graphic intensive applications such as games
require plenty of VRAM.

VRAM
Graphic intensive applications such
as games require plenty of VRAM.
Video Control Board
with Monitor Cable

Video Controllers

Standards of Monitors
 VGA: Video Graphic Array-

Supports 16 x 256 colors depending on the
resolution
 At 320 x 200 pixels: 256 colors

At 640 x 480 pixels: 16 colors
 SVGA: Super VGA-

800 x 600 pixels and 1024 x 768 pixels – 256 colors
 XGA: Extended Graphic Array-
 16.7 million colors at 1024 x 768 pixels

Paper Output
 In computer, paper output is sometimes
called Hard Copy.
 Hard copy can come from one of two
kinds of printers:
 Impact Printers
 Non-Impact Printers

Printer Categories
Printers fall into two categories:
 Impact printers use a device to strike an
inked ribbon, pressing ink from the
ribbon onto the paper.
 Non-impact printers use different
methods to place ink (or another
substance) on the page.

Impact Printers
 Line Printers
 Used by mainframes for massive jobs
 Limited characters available
 Dot-Matrix Printers
 Image formed from dots printed on paper
 Good for text and graphics
 Inexpensive

Dot Matrix Printers
 Dot matrix printers are a common type of
impact printer.
 A dot matrix printer's print head contains a
cluster of pins. The printer can push the pins
out to form patterns in rapid sequence.
 The pins press an inked ribbon against the
paper, creating an image.

2. chapter 2: Input-Output in Computer.ppt

Dot Matrix Printers
 Lower-resolution dot matrix printers use
nine pins. Higher-resolution models have
24 pins.
 Speed is measured in characters per
second (cps). Some dot matrix printers
print 500 cps.

Non-Impact Printers
 Laser Printers
 Image transferred to paper with laser
beam
 Faster and more expensive
than dot-matrix
 High-resolution hard copy

Laser Printer
 Laser printers are non-impact printers.
 They use heat and pressure to bond
particles of toner to paper.
 Laser printers provide resolutions from
300 – 1200 dpi(dot per inch) and higher.
 Black-and-white laser printers usually
produce 4 – 16 ppm.
 Laser printers produce higher-quality print
than ink jet printers, but are more costly

Laser Printer Working

Other Non-Impact Printers
 Ink-Jet Printers
 Dots of ink are sprayed onto the paper to
form the image
 High-resolution hard copy
 Some models print can print color
photographs

Ink-jet Printers
 Ink jet printers are an example of non-
impact printers.
 The printer sprays tiny droplets of ink
onto the paper.
 Ink jet printers are available for color and
black-and-white printing.
 Ink jet printers offer speeds of (2 – 4
pages per minute ppm) and resolution
(300 – 600 dots per inch dpi), comparable
to low-end laser printers.

Other Non-Impact Printers
 Plotters
 Image transferred to paper with ink pens
 Very high resolution
 Excellent for scientific and engineering applications
 They are mostly used for print-outs that are too
large to be printed by printers.

Types of Plotters
 Ink-jet Plotters: They work like ink-jet
printers
 Electrostatic Plotters: They work like a
photocopy machine. They are faster
and more expensive.

Printer Quality
When evaluating printers, consider four
criteria:
 Image quality– Measured in dots per inch
(dpi). Most printers produce 300 – 600 dpi.
 Speed– Measured in pages per minute (ppm)
or characters per second (cps).
 Initial cost– Consumer printers cost $250 or
less, but professional printers can cost
thousands of dollars.
 Cost of operation– This refers to the cost of
supplies used by the printer.

2. chapter 2: Input-Output in Computer.ppt

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