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Input and Output
UNIT 4 INPUT OUTPUT DEVICES Devices
- 4.0 Introduction Structure Page No.
- 4.1 Objectives
- 4.2 Input Output Devices
- 4.3 What is a Port?
- 4.3.1 Parallel Port
- 4.3.2 Serial Port
- 4.3.3 Universal Serial Bus (USB)
- 4.3.4 Small Computer System Interface (SCSI) Port
- 4.4 Input Devices
- 4.4.1 Keyboard
- 4.4.2 Mouse
- 4.4.3 Digitizing (Graphic) Tablet
- 4.4.4 Trackball
- 4.4.5 Joystick
- 4.5 Pick Devices
- 4.5.1 Light Pens
- 4.5.2 Touch Screens
- 4.6 Source Data Entry Devices
- 4.6.1 Digital Camera
- 4.6.2 Scanner
- 4.6.3 Optical Mark Reader (OMR)
- 4.6.4 Magnetic Ink Character Reader (MICR)
- 4.6.5 Bar-Code Reader
- 4.6.6 Magnetic Stripe Reader
- 4.7 Output Devices
- 4.7.1 CRT Monitor
- 4.7.2 LCD Monitor
- 4.7.3 Thin Film Transistor Liquid Crystal Display (TFT LCD)
- 4.7.4 LED Monitor
- 4.7. 5 Projection Displays
- 4.7. 6 Printers
- 4.7. 7 Plotters
- 4.7. 8 Speaker and Microphones
- 4.8 Summary
- 4.9 Answers to Check Your Progress
- 4.10 Further Readings
Basics of Computer
Hardware 4.0^ INTRODUCTION
In the previous unit, we have discussed the history of computer systems and methods to store data in computers. In this unit we shall discuss something about input/output devices and their functions. Input/output devices constitute a major part of a computer system. These are also called peripheral devices. Without I/O devices, a user cannot communicate with the computer. They are required to enter data and instructions in a computer so that the computer can process that data and provide the result to the user through output devices. In computer, inputs are the signals and data received by the system and outputs are the signals and data which are generated from the system.
First we will discuss briefly about input/output devices and then move on to the function and structure of input and output devices. And finally, we will discuss about recent trends in input devices such as digital camera, barcode reader, magnetic ink character recognition and magnetic stripe reader such as ATM machines and Electronic Point of Sale (EPOS).
4.1 OBJECTIVES
After studying this unit you should be able to understand:
the basic concepts of input/output devices; functions of input/output devices; types of input/output devices; types of Ports; types of monitors, printers, scanners and graphics tablet; and newer technologies in computer hardware.
4.2 INPUT OUTPUT (I/O) DEVICES
The computer will be of no use if it is not communicating with the external world. Thus, a computer must have a system to receive information from the outside world and must be able to communicate results to the external world. Thus, a computer consists of input/output devices. Input and output devices can also be written as I/O devices.
Input and output devices of a computer system are the devices that connect you to computer. Input devices let you to transfer data and user command into the computer system. I/O devices are used to interact with the computer system. For example, you can type in data by using a keyboard, or you can input data in picture form by using a scanner in computer system.
Inputs are data or signals received by the computer system. An Input unit takes the input and converts it into binary form, so that it can be understood by the computer
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reflects the inability of human-operated keyboards or keypunches to supply data at a speed that matches the speed of digital computers.
Check Your Progress - 1
Part I: State True/False
- Keyboard is an input device. True / False
- Monitor is an input device. True / False
- Printer is an input device. True / False
- Graphic Tablet is an input device. True / False
- Joy-stick is an output device. True / False
- Speaker is an output device. True / False
- Microphone is an input device. True / False
Part II: Short answer type questions
- What do you mean by input devices? …………………………………………………………………………………………. …………………………………………………………………………………………. ………………………………………………………………………………………….
- What do you mean by output devices? …………………………………………………………………………………………. …………………………………………………………………………………………. ………………………………………………………………………………………….
- Name some input and output devices. …………………………………………………………………………………………. …………………………………………………………………………………………. ………………………………………………………………………………………….
4.3 WHAT IS PORT?
Port is a connecting socket, outside the system into which different types of cables are plugged. It is a specific place from which other devices can be physically connected. I/O ports are the interfaces through which computers communicate with external devices such as printers, modems, joysticks and terminals. There are many types of ports used in computer system. Some of them are given as follows.
4.3.1 Parallel Port
Various peripherals can be connected through parallel port, which is a parallel communication physical interface. A parallel port transmits 8 bits of a byte of data in parallel. It is used for transmitting fast data over short distances. It is used to connect a printer to a computer. Since a parallel port transmits an entire byte at a time, it operates
I/O ports are the interfaces through which computers communicate with external devices such as printers, modems, joysticks and terminals
Input and Output Devices
I/O devices at a relatively high speed. A Parallel port is primarily used to connect printers to a computer and hence it is often called a printer port.
Figure 4.1: Parallel Port
4.3.2 Serial Port
Serial port transmits one bit of a byte, one at a time as a single stream of bits. It is meant for transmitting slow data over long distances. Communication over a phone is an example of serial communication. It is a serial communication physical interface which transmits one bit at a time. Dial-up modems and serial mice use serial ports.
Figure 4.2: Serial Port
4.3.3 Universal Serial Bus (USB)
A USB Port can connect up to 127 peripheral devices such as a digital camera, digital speakers, scanners, speakers etc. It permits Plug and Play – configuring of expansion cards and peripheral devices as and when they are installed.
Figure 4.3: USB
4.3.4 Small Computer System Interface (SCSI) Port
SCSI-Small Computer System Interface Port allows data to be transmitted in a daisy chain to up to 7 devices at a speed higher (32 bits at a time) than those possible with serial and parallel ports. It is a fast data transmitting device and is used to connect HDD, CD ROM drives and scanners with the computer system.
Input and Output Devices All the modern keyboards of computer are classified as:
(a) Original PC keyboard having 84 keys;
(b) Advance Technology (AT) Keyboard having 101-104 keys; and
(c) Multimedia Keyboard having 120 – 140 keys.
4.4.2 Mouse
A Mouse is a handy device which can be moved on a smooth surface to cause the movement of a cursor on the screen. It is a pointing device which is used to input data and information into the computer system by pointing on it. Physically, a mouse contains a small case, held under one of the user’s hands with one or more buttons. For GUI-based systems a mouse is an essential pointing-device. The cursor of the mouse moves in the same direction in which the mouse ball rolls.
Figure 4.5: Mouse
Its name is derived from its shape, which looks a bit like a mouse, with its connecting wire that one can imagine to be the mouse’s tail. A Mouse rolls on a small ball and has two or three buttons on the top. When you roll the mouse across a flat surface on the screen, sensors sense the mouse in the direction of mouse movement. The cursor moves very fast with a mouse giving you more freedom to work in any direction. It is easier and faster to move through a mouse compared to movement using keys.
Types of Mouse
Mouse could be mechanical, optical or cordless types. Further information regarding these types are as follows :
Mechanical Mouse : Mechanical Mouse uses ball for the movement of cursor on the computer screen. When the ball is rolled in any direction, a sensor of the mouse detects it and also moves the mouse pointer in the same direction.
Optical Mouse : Optical Mouse uses Laser rays for the movement of cursor on the computer screen. It is an advanced pointing device. Movement is detected by sensing changes in the reflected light rather than the motion of a rolling sphere.
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Cord-Less Mouse : Cord-Less Mouse is battery driven and does not need any wire for the physical connection with the motherboard. It transmits data through infrared or radio signal.
Computer mice are very useful in designing pictures and graphs and computer and video games by multimedia designers. A Mouse pad is required to move the mouse because it provides a smooth surface. However, an optical or laser mouse doesn’t require a mouse pad.
4.4.3 Digitizing (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. Some tablets are intended as a general replacement for a mouse as the primary pointing and navigation device for desktop computers. These are used by architects, engineers and designers in Computer Aided Design (CAD) for designing purposes, such as buildings, cars, mechanical parts, robots etc. These are also used in Geographical Information System (GPS) for digitizing of maps.
Figure 4.6: Graphics Tablet
Graphics tablet is most suited for artists and those who want the natural feel of a pen-like object to manipulate the cursor on their screen. Wacom is the most well known manufacturer of graphics tablets, and is incredibly well respected.
4.4.4 Trackball
Trackball is a moveable ball mounted on a stationary device, which can be rotated manually by using fingers. It is also a pointing device. In a trackball, the ball is placed on the top along with buttons which can be rolled with the fingers. These are used in playing video games.
Figure 4.7: Trackball
These are used by architects, engineers and designers in Computer Aided Design (CAD) for designing purposes, such as buildings, cars, mechanical parts, robots etc.
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- What do you mean by scanners and what are their functions?
- What do you mean by joystick and trackballs in a computer system?
4.5 PICK DEVICES
Pick devices are used to select an object on the screen. The selected object can be text or graphics. Examples of pick devices are light pens and touch screens.
4.5.1 Light Pens
A Light pen is a pen like light-sensitive device. It is connected by a wire to the computer terminal to detect the CRT beam when pointed towards the screen and generate a narrow electrical pulse that can be fed to the computer as an input signal. It is used to draw on the screen or to point to the displayed objects. It operates by detecting the light emitted by the screen phosphors.
A light pen can work with any CRT monitor but not with LCD monitors. It is used by architects and engineers for CAD applications and editing.
Figure 4.9: Light Pen
4.5.2 Touch Screens
Touch screens are monitors / electronic visual display screens which detect where they are being touched. The user makes selections by directly touching the screen, rather than moving a cursor to the point on the screen with a mouse or joystick Now days touch screens are being used in ATM machines for making it user friendly and Kiosk machines are used for guiding the travelers about their travel plans. Touch screens are also used in many of the modern cell phones.
A light pen can work with any CRT monitor but not with LCD monitors
Input and Output Devices
Figure 4.10: Touch Screen
4.6 SOURCE DATA ENTRY DEVICES
Entry of data into a computer system directly from the source, without transcription is called source data entry. Source data entry devices have a lower probability of error in input data than standard keyboard entry. Some of the common source data entry devices are discussed below:
4.6.1 Digital Camera
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 can do things which film cameras can’t, for example displaying images on screen immediately after they are recorded.
Images recorded on a digital camera can be cropped for editing, deleted and various types of special effects can be created by using Photoshop software.
Digital cameras look like ordinary cameras but have sufficient memory in the form of chips to store thousands of images, rather than using photographic films.
Figure 4.11: Digital Camera
Most digital cameras allow users to choose the resolution needed for a picture. Most of those can connect directly to a computer to transfer data. A USB port is generally used for this purpose. A Wireless connection can also be used for connecting to a computer via Bluetooth.
Input and Output Devices
4.6.4 Magnetic Ink Character Recognition (MICR)
Magnetic Ink C haracter Recognition is a character recognition system that uses special ink and characters. When a document that contains this ink needs to be read, it passes through a machine, which magnetizes the ink and then translates the magnetic information into characters.
MICR technology is used by banks for faster processing of large volumes of cheques. Numbers and characters found on the bottom of checks (usually containing the check number, sort number, and account number) are printed using Magnetic Ink. To print Magnetic Ink codes, we need a laser printer that accepts MICR toner.
MICR provides a secure, high-speed method of scanning and processing information. This technology is used for processing large volume of data. It speeds up data input for the bank because cheques can be directly fed into the input device as it also ensures accuracy of data entry. The most commonly used character set by MICR devices are known as E13B font which consists of the numerals 0 to 9, and four special characters.
4.6.5 Bar Code Reader
A barcode reader is an electronic device which is used to read printed barcodes. Barcodes represent alphanumeric data which is a combination of vertical lines (bars) that vary in width and length. 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.
Figure 4.14: Bar Codes Figure 4.15: Bar Code Reader
The bar code is 13 digits long and it has four main divisions. The First two digits of a bar code represent the country, the second part represents the manufacturer’s code (five digits) the third part represents the product code (five digits) and the last digit is a check digit.
4.6.6 Magnetic Stripe Reader
A magnetic reader is a hardware device which is used to read the information encoded in the magnetic stripe located at the back of a credit/debit card. A bank card holds data about the owner of the card, bank account number and code of the bank branch, where the account is held.
MICR technology is used by banks for faster processing of large volumes of cheques
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Figure 16: ATM Machine with Card Figure 17: Magnetic Stripe Reader
Magnetic stripe readers are often used at supermarkets and in many different types of shops. In these machines data is read electronically and the point of sale is called Electronic Point of Sale (EPOS).
There are several other pick devices such as microphones and speakers. These have been discussed in length under the section Out Put Devices section of this unit.
4.7 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.
4.7.1 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.
A Graphic display is made up of a series of dots called ‘ pixels ’ (picture elements) whose pattern produces images in computer system
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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.
4.7.3 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.
4.7.4 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.
4.7.5 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.
Figure 4.20 : LCD Overhead Projector
These are popularly used for seminars, class room lectures, marketing presentations and conference room presentations etc.
Input and Output Devices Classification of monitors on the basis of color
In terms of color capabilities, monitors can be divided into the following groups:
- 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.
- 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.
- 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:
- Analog Monitor
- 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.
The greater the number of pixels the sharper is the images
Input and Output Devices
- What do you mean by multimedia graphics tablet? ………………………………………………………………………………………… …………………………………………………………………………………………. ………..……………………..…………………………………………………………
- What do you meany by Computers Microphones? ………………………………………………………………………………………… …………………………………………………………………………………………. ………..……………………..…………………………………………………………
- What do you mean by barcode reader? ………………………………………………………………………………………… …………………………………………………………………………………………. ………..……………………..…………………………………………………………
- What do you mean by digital camera? Explain its various characteristics. ………………………………………………………………………………………… …………………………………………………………………………………………. ………..……………………..…………………………………………………………
4.7.6 Printers
Printers are used for producing output on paper. There are a large variety of printers and printing devices which can be classified according to the print quality and printing speed.
These varieties of printers are:
Printing Technology – impact printers vs. non impact printers
Impact printers use variations of the standard typewriter printing mechanism where a hammer strikes paper through an inked ribbon.
A non Impact printer uses chemical, heat or electrical signals to produce symbols on paper. Some of these require special coated or treated paper to print characters on them.
Classification of printers on the basis of speed :
On the basis of speed printers are of following types
- Character Printer : These printers can print only one character at a time. They work similar to a typewriter. The examples are Daisy Wheel Printer, Dot Matrix Printer and Inkjet Printer.
(a) Daisy-Wheel Printer : This printer is similar to a ball-head typewriter. This type of printer has a plastic or metal wheel on which the shape of each character is embossed.
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Figure 4.23: Daisy-Wheel Printer A hammer presses the wheel against a ribbon, which in turn makes an ink stain in the shape of the character on the paper. Daisy-wheel printers produce letter- quality print but cannot print graphics. The print quality of this impact printer is very low as is the speed. These are practically obsolete now.
(b) Dot-Matrix Printer : This is one of the most popular printers used for
personal computing systems. These printers are relatively cheaper
compared to other technologies and use impact technology.
In the 1970s and 1980s, dot matrix impact printers were generally considered the best tradeoff between expense and versatility, and until the 1990s they were by far the most common form of printers used with personal computers. Characters in this printer are formed by the combination of dots.
Figure 4.24: Dot Matrix Printer
A Dot-Matrix printer creates characters by striking pins against an ink soaked ribbon. Each pin makes a dot and combinations of dots form characters and illustrations. The moving portion of the printer is called the print head.
Figure 4.25: Characters as a pattern of dots
