Output Devices

Output Unit:

    The output unit of a computer provides the information and results of a computation to outside world.  Printers, Visual Display Unit (VDU) are the commonly used output devices.

Monitors:

    Monitors, commonly called as Visual Display Unit (VDU), are the main output device of a computer. It forms images from tiny dots, called pixels that are arranged in a rectangular form. There are three kinds of monitors are available.

• Cathode-Ray Tube (CRT)
• Liquid Crystal Display
• Light Emitting Diode Display

Cathode-Ray Tube (CRT) Monitor:

    In CRT monitors images are produced when an electron beam strikes a phosphor surface. Most of the desktop computer use the CRT monitors. This CRT monitors are similar to the "picture tube" in a television.

    A cathode ray tube consists of several basic components like, The electron gun generates a beam of electrons. The anodes accelerate the electrons. Deflecting coils produce an extremely low frequency electromagnetic field that allows for constant adjustment of the direction of the electron beam. The intensity of the beam can be varied. The electron beam produces a tiny, bright visible spot when it strikes the phosphor-coated screen.

Liquid crystal Display Monitor:

    Liquid Crystal Display (LCD) is a flat panel display technology commonly used in TVs and computer monitors. It is also used in screens for mobile devices, such as laptops, tablets, and smart phones.

    LCD displays don't just look different than bulky CRT monitors, the way they operate is significantly different as well. Instead of firing electrons at a glass screen, an LCD has back light that provides light to individual pixels arranged in a rectangular grid.

    The back light in liquid crystal display provides an even light source behind the screen. This light is polarized, meaning only half of the light shines through to the liquid crystal layer. The liquid crystals are made up of a part solid, part liquid substance that can be "twisted" by applying electrical voltage to them. They block the polarized light when they are off, but reflect red, green, or blue light when activated.

Light Emitting Diode:

    Light-Emitting Diode(LED) is an electronic device that emits light when an electrical current is passed through it. Early LEDs produced only red light, but modern LEDs can produce several different colors, including red, green, and blue (RGB) light. Recent advances in LED technology have made it possible for LEDs to produce white light as well. LEDs by a series of small lights that make up a larger display.

    The energy efficient nature of LEDs allows them to produce brighter light than other types of bulbs while using less energy. For this reason, traditional flat screen LCD displays have started to be replaced by LED displays, which use LEDs for the back light. LED TVs and computer monitors are typically brighter and thinner than their LCD counterparts.

Printers:

   Printer is an output device, which is used to print information on paper. Hard copy output produced by this output device. There are two types of printers −

• Impact Printers
• Non-Impact Printers

Impact Printers:

   Impact printers print the characters by striking them on the ribbon, which is then pressed on the paper.

Characteristics of Impact Printers are the following −

• Very low consumable costs
• Very noisy
• Useful for bulk printing due to low cost
• There is physical contact with the paper to produce an image

These printers are of two types −

• Character printers
• Line printers

Character Printers:

   Character printers are the printers which print one character at a time.

These are further divided into two types:

• Dot Matrix Printer(DMP)
• Daisy Wheel

Dot Matrix Printer:

    In the market, one of the most popular printers is Dot Matrix Printer. These printers are popular because of their ease of printing and economical price. Each character printed is in the form of pattern of dots and head consists of a Matrix of Pins of size (5*7, 7*9, 9*7 or 9*9) which come out to form a character which is why it is called Dot Matrix Printer.

Advantages:

• Inexpensive
• Widely Used
• Other language characters can be printed

Disadvantages:

• Slow Speed
• Poor Quality

Daisy Wheel:

   Head is lying on a wheel and pins corresponding to characters are like petals of Daisy (flower) which is why it is called Daisy Wheel Printer. These printers are generally used for word-processing in offices that require a few letters to be sent here and there with very nice quality.

Advantages:

• More reliable than DMP
• Better quality
• Fonts of character can be easily changed

Disadvantages:

• Slower than DMP
• Noisy
• More expensive than DMP

Line Printers:

    Line printers are the printers which print one line at a time.

These are of two types −

• Drum Printer
• Chain Printer 

Drum Printer:

    This printer is like a drum in shape hence it is called drum printer. The surface of the drum is divided into a number of tracks. Total tracks are equal to the size of the paper, i.e. for a paper width of 132 characters, drum will have 132 tracks. A character set is embossed on the track. Different character sets available in the market are 48 characters set, 64 and 96 characters set. One rotation of drum prints one line. Drum printers are fast in speed and can print 300 to 2000 lines per minute.

Advantages:

• Very high speed

Disadvantages:

• Very expensive
• Characters fonts cannot be changed

Chain Printer:

    In this printer, a chain of character sets is used, hence it is called Chain Printer. A standard character set may have 48, 64, or 96 characters.

Advantages:

• Character fonts can easily be changed.
• Different languages can be used with the same printer.

Disadvantages:

• Noisy 

Non-impact Printers:

     Non-impact printers print the characters without using the ribbon. These printers print a complete page at a time, thus they are also called as Page Printers.

These printers are of two types −

• Laser Printers
• Inkjet Printers

Characteristics of Non-Impact Printers:-

• Faster than impact printers
• They are not noisy
• High quality
• Supports many fonts and different character size

Laser Printers:

     These are non-impact page printers. They use laser lights to produce the dots on drum by polarization. This polarized drum rolled on toner (ink powder). This drum rolled on paper, that paper passes through heat chamber.

Advantages:

• Very high speed
• Very high quality output
• Good graphics quality
• Supports many fonts and different character size

Disadvantages:

• Expensive
• Cannot be used to produce multiple copies of a document in a single printing

Inkjet Printers:

    Inkjet printers are non-impact character printers based on a relatively new technology. They print characters by spraying small drops of ink onto paper. Inkjet printers produce high quality output with presentable features.

    They make less noise because no hammering is done and these have many styles of printing modes available. Color printing is also possible. Some models of Inkjet printers can produce multiple copies of printing also.

Advantages:

• High quality printing
• More reliable

Disadvantages:

• Expensive as the cost per page is high
• Slow as compared to laser printer