Input devices -> sensory organs—the eyes, ears, and fingers.
it enables us to enter information and commands into the computer
Most common input devices : keyboard & mouse.
Alternative input devices ?
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The Keyboard The most common input device, Skill is called keyboarding
IBM Enhanced Keyboard: Common layout, has 100 keys in five groups.
The Alphanumeric Keys : QWERTY,
Special functions: Tab, CAPS Lock, backspace, & Enter
Modifier Keys: SHIFT, ALT, & CTRL
Numeric Keypad: like calculator, 10 digits & operator (+ - */). NUM LOCK key
Function keys: input commands, depends on application, Fl = help.
Cursor-Movement Keys.
Special-Purpose Keys
Start Key(Windows logo), Shortcut key (Opens onscreen menu), Page Up / Page Down
Esc is used to “back up" one level in a multilevel environment.
The Print Screen key: capture screen as an image.
Scroll lock : cursor remain stationary, & document's contents move around It.
Pause Key : stop a command In progress
latest trends :addition of Internet & multimedia controls on keyboards 3A-4
How keyboard works – 5 steps 1)A key is pressed on the keyboard 2)The keyboard controller sends scan code for the key to
the keyboard buffer 3)The keyboard controller sends an interrupt request to the
system software. 4)The system software responds to He Interrupt by reading
the scan code from the keyboard buffer. 5)The system software passes the scan code to the CPU keyboard controller handles input from keyboard &
mouse and stores the settings for both devices. Repeat rate: determines how long you hold down a key
before keyboard will repeat the character.
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The Mouse All modern computers have a variant
Allows users to select objects
Pointer moved by the mouse
Mechanical mouse
Rubber ball determines direction and speed
The ball often requires cleaning
Inside the mouse, rollers and sensors send signals to the computer, telling it the distance, direction, and speed of the ball's motions
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The Mouse Optical mouse
Light shown onto mouse pad
Reflection determines speed and direction
Requires little maintenance
Interacting with a mouse
Actions involve pointing to an object
Clicking selects the object
Clicking and holding drags the object
Releasing an object is a drop
Right clicking activates the shortcut menu
Modern mice include a scroll wheel
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The Mouse Benefits
Pointer positioning is fast
Menu interaction is easy
Users can draw electronically
Mouse button configuration
Configured for a right-handed user
Can be reconfigured
Between 1 and 6 buttons
Extra buttons are configurable
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Variants of the Mouse Trackballs
Upside down mouse
Hand rests on the ball
User moves the ball
Uses little desk space
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Variants of the Mouse Track pads
Stationary pointing device
Small plastic rectangle
Finger moves across the pad
Pointer moves with the pointer
Popular on laptops
Track point
Little joystick on the keyboard
Move pointer by moving the joystick
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Pointing slows : Linux wins! Pointing, however, slows you down
As menus and dialog boxes become increasingly crowded, commands can be hard to find and their locations can be as difficult to re member as keyboard shortcuts.
The passive matrix LCD relies on transistors for each row and each column of pixels arranged in a grid
inexpensive, narrow viewing angle
Poor refresh rate : Animation are blurry (Submarining)
Dual-scan LCD: scans the pixels twice, for better results.
Active matrix LCD : assigns a transistor to each pixel
Each pixel is activated directly, Pixels have 4 transistors:
One each for red, green, blue, One for opaqueness
Thin-film transistor (TFT ) Technology.
Animation is crisp and clean
Monitors Paper-white displays
High contrast between foreground and background
Page-white display: LCD version of the paper-white.
Utilize a special technology, called supertwist, to create higher contrasts.
Electro-luminescent displays (ELD)
Uses phosphor film between 2 sheets of glass. A grid of wires sends current through the film to create an image
Plasma monitor
Sandwiches gas (neon / xenon) between 2 glass sheets
Monitors and Video Cards Monitors impacts user effectiveness
Monitors should have
Crisp text
Clear graphics
Adjustable controls
Clear edges
Monitors and Video Cards Size of monitor
Measured in inches
Measured diagonally
Actual size
Distance from corner to corner
Viewable size
Useable portion of the screen
Monitors and Video Cards Resolution
Number of pixels on the screen
Higher number creates sharper images
Higher number creates smaller images
VGA standard 640 X 480 : horizontally X vertically
SVGA expanded resolutions : 800 X 600 & 1024 X 768
Monitors and Video Cards Refresh rate
Number of time the screen is redrawn
Modern equipment sets this automatically
Improper settings can cause eyestrain
phosphor dots fade quickly after the electron gun charges them with electrons. If the screen is not refreshed often enough, it appears to flicker which causes of eyestrain
Refresh rate is measured in Hz: cycles / sec, this means that if a monitor’s refresh rate is 100 Hz, it refreshes its pixels 100 times every second.
Monitors and Video Cards Dot pitch
Distance between the same color dots
Ranges between .15 mm and .40 mm
Smaller creates a finer picture
Should be less than .22
Video Cards Device between the CPU and monitor
Better cards result in better output
Removes burden of drawing from CPU
Have their own processor and RAM
Modern cards have up to 512 MB RAM
Capable of rendering 3D images
Ergonomics and Monitors Eyestrain
Fatigue of the eyes
Steps to avoid
Choose a good monitor
Place the monitor 2 – 3 feet away
Center of screen below eye level
Avoid reflected light
Electronic magnetic fields (EMF) Generated by all electronic devices
EMF may be harmful to health
Steps to avoid
Keep the computer at arms length
Take frequent breaks
Use an LCD monitor
Data Projectors Replaced overhead and slide projectors
Project image onto wall or screen
LCD projectors
Most common type of projector
Small LCD screen
Very bright light
Require a darkened room
Digital Light Projectors (DLP)
A series of mirrors control the display
May be used in a lighted room
DLP vs LCD working
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Sound Systems Integral part of the computer experience
Capable of recording and playback
Sound card
Device between the CPU and speakers
Converts digital sounds to analog
Can be connected to several devices
Modern cards support Dolby Surround Sound
Sound Systems Headphones and headsets
Replacement for speakers and microphones
Offer privacy
Does not annoy other people
Outside noise is not a factor
Headsets have speakers and a microphone
Review Questions 1. There are two basic types of monitors used with PCs. List them.
2. How does a color CRT monitor produce images on the screen?
3. What are two disadvantages of CRT monitors, compared to flat-panel displays?
4. What are two disadvantages of LCD monitors, compared to CRT monitors?
5. How does a plasma display monitor work?
6. List the four factors you should consider when comparing monitors.
7. As it relates to monitors, what does the term '’resolution'’ refer to?
8. What is dot pitch?
9. How should you position your monitor, if you want to avoid eyestrain?
10. How does digital light processing (DLP) technology work? 3A-46
