OUTPUT DEVICES
One of the most important output devices in computer system is its screen commonly called monitor. It is an output device and displays all the programs and applications which are running on the computer system. A Monitor is the visual display unit of the computer system. It displays images generated from the video output. It displays images without keeping a permanent record.
A Graphic display is made up of a series of dots called 'pixels' (picture elements) whose
pattern produces images in computer system. Each dot on the screen is defined as a separate unit which can be addressed separately. Since each dot on the screen can be controlled separately it gives greater flexibility in drawing pictures. The Number of dots per inch (dpi) is called the resolution of the screen and represents the quality of the computer system.
Cathode Ray Tube Monitors (CRT)
Monitors display what is going on in your computer. They can run at various resolutions. It is the part of computer which looks like a TV set. After typing the characters from the keyboard, we can see them on the monitor.
The main components of a CRT monitors are the electron gun, the electron beam controlled by an electromagnetic field and phosphor coated display screen. These older monitors are bulky and require a lot of space for installation.
In CRT monitors, the image is projected on the screen by directing the electron beam onto the computer screen. To precisely direct the electron beams, copper steering coils are used to create a magnetic field inside the tube. By applying varying voltages to the copper coils a beam can be positioned at any point on the screen.
Liquid Crystal Displays (LCD)
First introduced in watches and clocks in the1970's, LCDs are now used to display images in monitors. A newer technology in computer screens is TFT LCD monitors. These are light weight monitors and are used in laptop computers. Active matrix structure is used by most of the modern LCD monitors and television sets. In this technology, a matrix of thin-film transistors (TFT) is added to the polarizing and color filters. It enhances the display to make it look brighter and sharper. It can also produce much better images and have quicker response times.
These monitors are portable, reliable and consume less electricity. Images produced by these monitors are of better quality than that of old CRT monitors. The LCD monitors have very high resolution and emit less radiation than CRT monitors. The screen is also flicker free.
Thin Film Transistor Liquid Crystal Display (TFT LCD)
It is type of monitor which used thin film transistor technology to enhance the image quality of LCD Monitors. These are used as monitor in television set, desktop computer, laptop computer and mobile phones etc.
Light Emitting Diodes Monitors (LED)
Light Emitting Diodes (LED) is the latest technology which is being used now a days for making high definition TV screens and monitors. It is a semi-conductor light source. In this technology diodes are used to light up the screen instead of liquid crystal Diodes.
LED is known as light emitting diode. It is an electronic device that lights up when electricity is passed through it. LEDs are usually red. They are good for displaying images because they can be relatively small, and they do not burn out. However, they require more power than LCD monitors. LED is light weight monitors and is used in laptop computers and in TV.
The Life of LED monitors is three times than that of LCD monitors and they have less warm up time than that of CRT or LCD monitors. These monitors require less space on the desk, less power consumption and have flicker free screen.
Projection Displays
These are normally used for large group presentations. These systems can be connected to a computer and whatever appears on the computer terminal gets enlarged and projected on a large screen. Video projector receives video signals and projects the corresponding image on a projection screen. It uses a lens system for this projection.
These are popularly used for seminars, class room lectures, marketing presentations and conference room presentations etc.
Classification of monitors on the basis of color
In terms of color capabilities, monitors can be divided into the following groups:
1. Monochrome : These monitors display the result in two colors, i.e., black/white, green/black, amber/black. One color is for the background of the screen and other for the foreground.
2. Gray Scale: It is a monochrome type of monitor. But it displays the output by using different shades of gray, made by a combination of black and white.
3. Color Monitor: It can display the output in many colors, ranging from 16 to over 1 million different colors. These are also called as RGB monitors, because they accept three separate signals, which are red, green, and blue.
Classification of monitors on the basis of size
After color classification, the most important aspect of a monitor is its screen size. The Size of computer screen is measured in diagonal inches and is given by measuring the distance from one corner to the opposite corner (diagonally). The smallest size for VGA monitors is 14 inches, which is also the entry level monitor for most computer systems. The Larger size landscape monitors can display two full pages side by side at a time. Other typical monitor sizes are 17 inches, 20 inches, 23 inches etc.
Classification of monitors on the basis of Resolution
The resolution of a monitor means the number of pixels per inch appearing on its surface. In general the greater the number of pixels the sharper is the images. Most modern monitors can display 1024 by 768 pixels. Some high-end models of computer monitors can display 1280 by 1024, or even 1600 by 1200 pixels. Even 3280 by 2048 resolution monitors are available for special purposes. While CRTs provide variability in resolution LCDs monitor have a fixed resolution.
Classification of monitors on the basis of signal
Computer monitor can be divided into two categories on the basis of the type of signal which they accept. These are:
1. Analog Monitor
2. Digital Monitor
Analog Monitor
The Electronic signal that is sent by signals of varying frequency, amplitude or phase instead of being sent as an ON or OFF data transmission is called an analog signal. Analog signals allow equipment to handle information that continuously changes such as voltage, current, etc.
Analog signals can be represented by a wave sign and watches which changes their position continuously as shown in Figure.
These are the traditional type of color monitors and are based on CRT technology. These work like the television screen and accept analog signals.
Digital Monitor:
An electronic signal that is sent as binary digits of either ON or OFF is called a Digital signal. As shown in Figure 4.22 examples of digital signals and how they look like. In the first diagram signals are either 0 or 1 i.e. up or down for ON and OFF mode. In the right digital pictures are shown where a pixel is either ON or OFF helping to create an image on the display screen.
The digital monitor receives digital signals and can use CRT technology. The data in these monitors is received from the video adapter. These are of different types such as CGA (Color Graphics Adapter), EGA (Enhanced Graphics Adapter), VGA (Video Graphics Array), and SVGA (Super Video Graphics Array). These are fast and produce clear images.
Check Your Progress
Part I: True / False
1)
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Pick devices are used to pick objects on the monitor
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True / False
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2)
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CRT monitors consume more electricity than LCD monitors
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True / False
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3)
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Light Emitting Display is the full form of LED monitors
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True / False
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4)
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Bar Code Reader is an OUT PUT Device
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True / False
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5)
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A Graphics tablet can be used as a mouse.
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True / False
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6)
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Graphic tablets are used for designing purposes.
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True / False
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(1) True (2) True (3) True (4) False (5) True (6)True
Part II: Short answer type questions
1) What is the function of Graphic Tablet?
Digitizing or Ggraphics' tablet is a computer input device that allows one to hand-draw images and graphics, similar to the way one draws images with a pencil and paper. These tablets may also be used to capture data of handwritten signatures.
2) What do you mean by multimedia graphics tablet?
A graphics tablet is a computer input device that allows one to hand-draw images and graphics, similar to the way one draws images with a pencil and paper with the natural feel
of a pen-like object to manipulate the cursor on their screen. These tablets are used to capture data of handwritten signatures. Architects, engineers and designers use it in
Computer Aided Design (CAD) for designing purposes.
3) What do you meany by Computers Microphones ?
A microphone is an acoustic-to-electric transducer or sensor that converts sound signals into electrical signals. A microphone is an input device which converts the sound and
voice into digital signal and then gives it to the computer for further processing.
4) What do you mean by barcode reader?
A barcode reader is an electronic device which is used to read printed barcodes. It is a fast and effective way to input data. A Barcode reader uses a laser beam to read the
series of thick and thin lines which represent the bar code number.
5) What do you mean by digital camera? Explain its various characteristics.
A Digital camera is an electronic device which takes video or still photographs or both, digitally by recording images via an electronic image sensor. Digital cameras have
sufficient memory in form of chips. Most digital cameras allow users to choose the resolution. The digital cameras can connect directly to a computer to transfer data. A
Wireless connection can also be used for connecting to a computer via Bluetooth. These cameras use memory cards with flash memory to store images.
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