Lecture # 4

Output Devices

Output Devices

• Devices that convert machine language into human understandable form.

• Output can be in display form, on paper or sound on speakers.

Output Devices• Monitor

• Sound System

• Printer

Monitors

• Monitors are the most commonly used output devices.

• A peripheral device with a screen for the visual display of information.

Types of Monitor

• Cathode ray tube (CRT)

• Flat-panel display

Monitors - CRT Monitors

• CRTs are the most common way of displaying images today.

• It uses a large vacuum tube called Cathode-Ray Tube.

CRT Monitors

Working of CRT

Scanning Mechanism

Monitor Categories Based on Color Display

Monochrome:

One color= Background, Other Color=Foreground

Color: RGB (Red, Green, Blue)

From 16 to 16 million unique colors.

Flat-Panel Monitors

• A monitor that uses an LCD panel or Plasma .

• Flat-Panel monitors are lighter in weight and require less power.

Flat-panel monitors take up less desk space.

Liquid Crystal Display (LCD) Monitor

•Most common flat-panel monitor.

•It creates images with a special kind of liquid crystal that is normally transparent.

•It becomes opaque when charged with electricity.

Two Categories of Liquid Crystal Displays

• Passive matrix LCD

• Active matrix LCD

Flat-Panel Monitors

• 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.

Other Kinds of Monitors

• Paper-white display

• Electroluminescent (ELD) display

• Plasma/gas plasma display

Considerations When Monitor Shopping

• Size• Resolution• Refresh rate• Dot pitch

Comparing Monitors - Size

• A monitor's size is the diagonal measurement of its face, in inches.

• Larger monitors are available, but can be expensive.

The diagonalsize (often 17”)

Size of Laptop vs. Size of CRT???????

Comparing Monitors - Resolution

• It is defined as a sharpness of a screen.

• Resolution = No. of pixels on the screen

• More the number of pixels, the better the resolution is.

• The Video Graphics Array (VGA) standard is 640x480. Super VGA (SVGA) monitors provide

resolutions of 800x600, 1024x768 or higher.

What happens as Resolution increases….????

Comparing Monitors - Refresh Rate

• Refresh rate = No. of times per second that the electron guns scan the screen's pixels.

• It is measured in Hertz (Hz) or cycles per second.

• Look for a refresh rate of 72 Hz or higher.

• It controls flicker.

• A slower rate may cause eyestrain.

Refresh Rate of Active Matrix LCD vs.Passive Matrix LCD

???????

Comparing Monitors - Dot Pitch

• Dot pitch is the distance between pixels.

• Closer the dots, crisper the image.

• Look for a dot pitch no greater than .28 millimeter.

Viewing Angle

•The angle from which the display’s image can be viewed clearly.

•CRT Monitors

•LCD

Viewing Angle of Active Matrix & Passive

Matrix LCD????????

Interlaced & Non-Interlaced Monitors

Interlaced Monitors: It scans odd lines in the first pass and in the second pass

scans the even lines. It causes flickering of screen.Obsolete.

Non-Interlaced Monitors: It scans an entire line of pixels at a time.No flickering.Commonly used.

Video Controller• Intermediary device

between the CPU and the monitor.

• Controls how things look on-screen.

Monitors - 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).

VRAM

Graphic intensive applications suchas games require plenty of VRAM.

Video Control Board with Monitor Cable

PC Projectors• A PC projector connects to a PC and is used to

project images on a large screen.

• Many PC projectors provide the same resolutions and color levels as high-quality monitors.

• Digital light processing (DLP) projectors use a microchip containing tiny mirrors to produce very sharp, bright images.

Projected Screen

Sound Systems

• Multimedia PCs come with a sound card, speakers, and a CD-ROM or DVD drive.

• A sound card translates digital signals into analog ones that drive the speakers.

• With the right software, you can use your PC to edit sounds and create special sound effects.

Sound Card•Translates digital sounds into the electric current that is sent to the speakers.

Sound Card• The most basic sound card is a printed circuit board

that uses four components:

1. An analog-to-digital converter (ADC) 2. A digital-to-analog converter (DAC) 3. An interface to connect the card to the motherboard.4. Input and output connections for a microphone and

speakers.