Computer 11 Notes for Computer Notes

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Output Devices


It is also known as VDU (Visual display unit). It is the most basic output device. It is used to display the output. Types of monitor on the basis of color display are:

1. Monochrome monitor
It is a single colored monitor. It can display only text and images of a single color against a contrasting background. The first monitor displayed text and images of light green color against black background.

2. Gray scale monitor
It can display 256 different variations of black and white color. It can also display video. The first television set was gray scale.

3. Color monitor
It can display 16-42 million colors. It uses 3 basic colors Red, Blue and Green. All the other colors are the combination of these colors. Color monitor is also known as RGB monitor.

Types of monitor on the basis of architecture:

- CRT Monitor
CRT is the large bulky sized monitor. It has high power requirement so it is not appropriate for portable devices. It is cheaper and has better brightness so, it is preferred by graphic designers.

Merits of CRT monitor are:

  • It has better brightness.
  • It is cheaper in cost.
  • It is more durable.
  • It has better graphics and larger viewing angle (~180)

De-merits of CRT monitor are:

  • Due to its high brightness human eyes are negatively affected.
  • It requires high power.
  • It is large in size so occupies more space.
  • It is not portable.

Flat panel monitor

LED contains multiple small bulbs. The contents are displayed by turning the bulbs “on” and “off”. Initially it was used only for simple digital displays like in calculator, digital watch, etc. At present it is also used in television, desktop PC, laptop, etc.

Merits of LED are:

  • It is light in weight so, it can be used in portable devices.
  • It requires less power.
  • It is small in size.
  • Its viewing angle is larger compared to LCD.

De-merits of LED are:

  • It has low brightness but is better than LCD and plasma.
  • It is expensive compared to CRT.
  • It is difficult to maintain.

LCD contains liquid crystals in between two plates of the screen. The plates are made by either glass or plastic. The front plate is transparent and the back plate is reflective. Liquid crystals are charged electronically to display the content. This monitor is popular for portable devices because of its small size, light weight, low power requirement however it has low brightness and it requires viewing angle of almost 90.

Merits of LCD:

  • It is small in size.
  • It is light in weight.
  • It has low power requirements so, can be used in portable devices.
  • It is cheaper than LED and plasma display.

De-merits of LCD:

  • It has low brightness.
  • It is expensive compared to CRT.
  • It requires viewing angle of almost 90.

Plasma display
It contains neon gas in between the two plates of the screen in place of liquid crystals of LCD. It has larger viewing angle but is expensive than LCD. It is smaller in size, light in weight and it has low power requirement and low brightness.

Merits of plasma display:

  • It is smaller in size and light in weight.
  • It has low power requirement so can be used in portable devices.
  • It has larger viewing angle.

De-merits of plasma display:

  • It has low brightness.
  • It is expensive than LCD.

Working mechanism of CRT:
A monochrome CRT contains single electron gun which emits beam of electrons. These electrons are attached towards positive phosphorous screen. When an electron strikes the screen it glows and emits light. A small area in which an electron strikes is known as pixel. To display a screen all the pixel are striked by electrons. Accelerating anode varies the speed of the electron and deflecting system changes the path of the electron.
A color CRT monitor contains three electron guns which emits three electrons at a time. These electrons converge in the same pixel to display a color.
Speaker is a soft copy output device for audio. It generates analog sound wave from stored digital sound by using vibrators. Different types of speakers vary on the loudness of sound generated. Some of the speakers used are:

  • Ear phone
  • Head phone
  • Normal speaker
  • Woofer
  • Loud speaker

Hard copy output devices:
Printer makes the permanent impression of color on the printing material like paper, plastic, clothes, rubber, metal, etc. A printer can be single or multi-colored. Types of printer are:

1. Impact printer
It prints by physically touching the printing material. It is noisier, slower for printing, single colored. It produces low quality output. It is usually cheaper and it can produce multiple copies at the same time by using carbon paper. It uses ink ribbon for printing.

Dot matrix printer
Daisy wheel printer
Line printer

2. Non impact printer
It prints without touching the printing material. It sprays liquid or powder ink. It uses electromagnetic or electrostatic mechanism. It is noiseless, faster for printing usually expensive, it has high printing quality, it can be single or multi-colored, it cannot produce multiple copies at the same time.
Example: ink jet printer, laser printer, thermal wax printer.

Printer can also be classified as:

  • Character printer
  • Line printer
  • Page printer

- Plotter:
It is large sized printer. It is used to plot large maps, designs, advertisements, etc. It is multi-colored, slow for printing, expensive and large in size. Paper, plastic (mainly flex) is used as printing material. It uses technology like ink jet technology, color pen technology. Ink jet technology uses liquid ink whereas color pen technology uses multi colored pens controlled by the mechanical arm. Ink jet is cheaper and color pen has better printing quality.

Different plotters in use are:

  • Drum plotter
  • Flat bed plotter
  • Micro grip plotter

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