Page 66 - Computer - 9(A&B)

The three most commonly used monitors are:
CRT (Cathode Ray Tube) Monitor
It works just like a TV which has a CRT, made up of glass an having an electron gun fi xed
at the back. The gun fi res electrons at a group of phosphorous dots present on the screen
which glows to give the desired color to form an image. These types of monitors are quite
bulky in size and are almost obsolete nowadays.

LCD (Liquid Crystal Display) Monitor
This is a new technology which is rapidly replacing the CRT monitors. In these, a material called liquid crystal,
is sandwiched between the two polarisable glass sheets. When the electric current passes through the crystals,
they block the light to create pixels. In each pixels of the LCD, there is a device called TFT (Thin Film Transistor)
which sets the charge to make them work. That’s why they are also known as TFT- monitors. They consume less
power than CRT monitors.

LED (Light-Emitting Diode) Monitor
LED Monitor is called “Light Emitting Diode” monitor. It is a fl at panel computer monitor
which is reliable but more expensive than LCD monitor.

Printer

Printer is an output device used to get hard copy of the results produced by the computer. Such type of output
is printed on a paper which is permanent in nature, i.e., it cannot be changed once it is produced.
On the basis of printing technology, printers can be divided into two categories: Impact printers and Non-
Impact printers.
Impact Printers

In these types of printers, the printer head with moulded characters strikes the paper through an inked ribbon
to leave the impression on the paper. Due to this mechanical contact, they produce a lot of noise while printing.
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Print quality is generally measured in DPI (Dots Per Inch).

The advantages of these types of printers are low operating cost and robustness. Some examples of impact
printers are:
Dot Matrix Printers: These are widely used character printers which print one character at a time. In these, the
print head contains an array of tiny hammers which comes out and strike the ribbon to producea the desired
output. The head moves to and fro to print in both the directions. The print quality in these type of printers,
depends on the number of hammers present in the print head. There are 9 pins and 24 pins dmps (dot matrix
printers) available in the market and they can print 30 to 600 cps (characters per second). These printers are less
expensive but very noisy.

Daisy Wheel Printers: These printers are also known as letter quality printers.
In these, the print head, shaped like a daisy fl ower has unchangeable characters
fi tted on it. The print head rotates continuously at a high speed and hammers the character
on the paper when it is in position. It is used for high quality printout but its speed is very
slow. It can print upto 90 cps.

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