Input devices
An input device can be defined as an electromechanical device that allows the user to feed data into the computer for analysis and storage and to give commands to the computer. The data is entered into the main memory through the input devices. They accept instructions from the user and convert the accepted instructions into the machine language. Some of the commonly used input devices are keyboard, mouse, trackball, joystick, light pen, touch screen, barcode reader, OMR, OCR, MICR, smart card reader, a biometric sensor, scanner, Mic, webcam, PC card, etc. which are described below.
Keyboard
It is one of the most common input devices. The user can type text and commands using this device. The layout of the keyboard was borrowed from the regular typewriter with some additional keys. The keyboard is used to enter data or information in a computer system, which may be in numeric form or alphabetic form. When a key is pressed, the keyboard interacts with a keyboard controller and keyboard buffer. The keyboard controller stores the code of the pressed key in the keyboard buffer. There are different types of keyboards such as QWERTY, DVORAK, and AZERTY.
Types of Keys on Keyboard
The keys are categorized under the following groups
- Alphanumeric Keys: Alphanumeric Keys include the alphabet keys (A, B, C, ..., Z) and number keys (0, 1, 2, 3, ..., 9).
- Numeric Keys: Numeric Keys are located on the right-hand side of the keyboard. They consist of digits and mathematical operators.
- Function Keys: Function Keys are programmable keys, i.e. the programs can assign some specific actions. They are numbered from F1 to F12.
- Cursor Control Keys: Cursor Control Keys include four directional (left, right, up, down) arrow keys that are arranged in an inverted T formation between the alphanumeric and numeric keypad. Above the arrow keys, there are four more keys to control the cursor. These are as follows
- Home: It is used to return the cursor to the beginning of the line or the beginning of a document.
- End: It moves the cursor to the end of the line.
- Page Up: When it is pressed, the page view will be moved up one page and the cursor goes to the back page.
- Page Down: When it is pressed, the page view will be moved down one page and the cursor goes to the next page.
- Other Keys: A keyboard contains some other keys such as follows
- Control Key: It performs a special operation with the combination of other keys.
- Enter Key: It is used to finish an entry and begin the new entry in a document. Enter key is an alternative to pressing the ok button.
- Shift Key: Some keys on the keyboard like numeric keys have a symbol printed on their upper portion. The shift key is used to print these symbols. This key is also called a combination key.
- Escape Key (Esc): It allows a user to cancel or abort operations, which are executing at present. It opens the Start menu with the combination of the Ctrl key.
- Backspace Key: It is used to erase anything typed.
- Delete Key: It is used to erase information from the computer’s memory and characters on the screen.
- Caps Lock Key: It is used to type the alphabet in capital letters. It enables or disables all the letters from being typed in capital letters. When this key is enabled, the alphabet would be in capital letters and when it is disabled, the alphabet would be in small letters.
- Num Lock Key: It is used to enable and disable the numeric keypad.
- Windows Key: It is used to open the Start menu.
- Spacebar Key: It provides a space between two words. It is the longest key on the keyboard.
- Tab Key: It is used to move the cursor over to the right to a pre-set point. In a Word document, the tab is used to indent a paragraph.
QWERTY keyboard contains a total of 104 keys.
Caps Lock and Num Lock keys are called ‘toggle keys’ because when pressed, they toggle or change their status from one state to another.
Shift, Ctrl, and Alt keys are also known as modifier keys.
Pointing Devices
A pointing device is used to communicate with the computer by pointing to the locations on the monitor. Movements of the pointing device are echoed on the screen by movements of the pointer. Some commonly used pointing devices are a mouse, trackball, joystick, light pen, touch screen, etc. which are described below:
Mouse
It is a small handheld device having two buttons on its upper side and also has a small wheel between these buttons. It is a pointing device that provides a means to input data and commands in graphic form by selecting through moving an arrow called a pointer on the monitor.
The mouse may be used to position the cursor on screen, move an object by dragging or select an object by clicking. Mouse was invented by Douglas Engelbart at Stanford Research Center in 1963. There are three types of mice as follows
- Wireless mouse
- Mechanical mouse
- Optical mouse
There are four actions of the mouse as follows
- Click or Left Click It selects an item on the screen.
- Double Click It is used to open a document or program.
- Right, Click It displays a list of commands on the screen. Right-clicking is used to access the properties of the selected object.
- Drag and Drop It is used to move an item on the screen.
Trackball
It is another pointing device that is an alternative to a mouse. A trackball is also used to control cursor movements and actions on a computer screen. It is generally a built-in laptop since there is no space for the mouse to move on the laptop. A trackball is used on CAD/CAM workstations and sometimes seen on computerized special purpose workstations such as radar consoles in an air-traffic control room and sonar equipment on a ship or submarine.
Joystick
It is a device that moves in all directions and controls the movement of the cursor. Joysticks are used in flight simulators, CAD/ CAM systems, etc. A joystick is similar to a mouse except that the movement of the cursor on the screen stops working as soon as the user stops moving the mouse. But with a joystick, the pointer continues moving in the previously pointing direction. The joystick allows movements in all directions (360°).
Light Pen
It is a handheld electro-optical pointing device, which is used for making drawings, graphics and for menu selection. The pen contains a photocell in a small tube. It senses the light from the screen when it becomes closer and generates a pulse. It is used to especially in Personal Digital Assistants (PDA). It is very useful in identifying a specific location on the screen. However, it does not provide any information when it held over a blank part of the screen.
Touch Screen
It is an input device that accepts input when the user places a fingertip on the computer screen. Touch screens have an infrared beam that crisscross the surface of screen. The ability to interact directly with a display typically indicates the presence of a touch screen. Touch screen is generally used in applications like ATM, hospitals, airline reservation, supermarkets, etc.
Barcode Reader
It is an input device used for reading printed barcodes (Universal Product Code) available on product to be sold. A barcode reader emits a beam of light which reflects off the barcode image. A light sensitive detector in the barcode reader identifies the barcode image by recognizing special bars at both the ends of the image. A perfect example of a barcode reader, use in a super market where barcode scanner reads the price of a product. A barcode is a machine-readable representation of information in the form of stripes of dark and light ink.
Optical Mark Reader (OMR)
OMR is also known as Optical Mark Recognition. It is the process of detecting the presence of intended marked responses. OMR is mainly used 22 Learn, Revise & Practice ~ Computer Awareness Trackball Barcode Reader Joystick 5050574807678 Barcode to detect marks on a paper. It uses a beam of light that is reflected on the paper with marks, to capture presence and absence of data (marks). The OMR interprets the pattern of marks into a data record and sends this to the computer for storage, analysis and reporting. OMR is widely used to read the answer of objective type tests, voting applications and other evaluation studies.
Optical Character Recognition (OCR)
OCR is a technique for the scanning of a printed page, translating it and then using the OCR software to recognize the image as ASCII text that is editable. It translates the array of dots into text that the computer can interpret as words and letters. OCR is widely used technique for acquiring the textual data from image. It is used in many applications such as telephone bills, electricity bills, insurance premium, etc. OCR technology is being developed for greater accurate recognition and is also known as Intelligent Character Recognition (ICR).
Magnetic Ink Character Recognition (MICR)
MICR reads the characters by examining their shapes in a matrix form and the information is then passed on to the computer. The characters are printed using a special ink, which contains iron particles that can be magnetized. It is generally used in banks to process the cheques for recognizing the magnetic encoding numbers printed at the bottom of a cheque.
Smart Card Reader
It is a device which is used to access the microprocessor of a smart card. There are two kinds of smart cards; Memory cards and Microprocessor cards. Memory cards are the cards which contain only non-volatile memory storage components and some specific security logic. Microprocessor cards contain volatile memory and microprocessor components. The card is made-up of plastic generally PVC. Smart cards are used in large companies and organizations for stronger security authentication.
Biometric Sensor
It is a device which recognizes physical or behavioral traits of the individual. Biometric sensors are used for marking attendance of employees/students in organizations/institutions. As biometric sensors are working with accuracy so these are widely used in security purpose also.
Scanner
It is used to convert the data and image on paper into the digital form. Scanner is an optical input device and uses light as an input source to convert an image into an electronic form that can be stored on the computer. Scanners can be used for storing the documents in their original form that can be modified and manipulated later on. Scanner stores images in both gray scale and color mode. The most common types of scanners are as follows
- Handheld Scanners: They are very small in size which can be held in a hand. These are less expensive and less wide. Hence, in order to scan a single page image, multiple passes are required. But their handiness is a major advantage of handheld scanner.
- Flatbed Scanners: They are large and more expensive scanners that create high quality images. Flatbed scanners have a flat surface on which the printed image to be scanned, is placed. These scanners can scan a page in a single pass.
- Drum Scanners: They are medium size scanners with a rolling drum. The sheet is fed through the scanners so that the drum rolls over the entire sheet to be scanned (just as the sheets are fed in a fax machine).
Microphone (Mic)
We can send input to the computer through a special manual input device called microphone or mic. A mic converts the received sound into computer’s format, which is called Digitized Sound or Digital Audio.
To convert a voice into digital form, you need an additional hardware known as Sound Card. Sound is used most often in multimedia, where we can make our presentations more attractive using recorded narration, music or sound effects.
A microphone can be attached to a computer to record sound. Now-a-days, microphones are also being used with speech recognition software. This means that we do not have to type, rather just have to speak and the spoken words appear in our document.
Webcam (Web Camera)
It is a video capturing device. Webcam is a digital camera attached to computers and can be used for video conferencing, online chatting, etc. A camera connected to a computer allows anyone, those are connected to the Internet, to view either a still picture or motion video of a user or other object.
Now-a-days, Webcams are either embedded into the display with laptop computers or connected via USB or firewire port or Wi-Fi to the computer.
PC Card
A PC card is a credit card size memory or I/O device that fits into a personal computer, usually a notebook or laptop computer. Probably the most common use of a PC card is the telecommunications modem for notebook computers.
Output Devices
An output device is any piece of computer hardware equipment used to communicate the results of data processing carried out by an information processing to the outside world. Some of the commonly used output devices are monitor, printers, plotter, speaker, headphones, projector etc. which are described below.
Monitor
It is also known as Visual Display Unit (VDU). The monitor is provided along with the computer to view the display result. A monitor is of two kinds; monochrome display monitor and colour display monitor. A monochrome display monitor uses only one colour to display text and colour display monitor can display 256 colours at a time. An image on the monitor is created by a configuration of dots, also known as pixels. The refresh rate of monitor is measured in Hertz (Hz). The clarity of image depends on three factors which are as follows
- Resolution of Screen: Resolution refers to the number of pixels in horizontal and vertical directions. The resolution of monitor is higher when the pixels are closer together.
- Dot Pitch: It refers to the diagonal distance between two coloured pixels. The smaller the dot pitch, the better the resolution.
- Refresh Rate: It is the number by which per second. The higher the refresh rate, the more solid the image looks on the screen. The popular types of monitors are as follows
Cathode Ray Tube (CRT)
It is a typical rectangular shaped monitor that you see on a desktop computer. The CRT works in a same way as a television. CRT has a vacuum tube. CRT works by moving an electron beam back and forth across the back of the screen. A screen covered with a fine layer of phosphorescent elements, called phosphores.
Liquid Crystal Display ( LCD)
These screens are used in laptops and notebook sized PCs. A
special type of liquid is sandwiched between two plates. It is a thin, flat and
light weight screen made up of any number of color or monochrome pixels
arranged in front of a light source.
Liquid/Light Emitted Diode (LED)
It is an electronic device
that emits light when electrical current is passed through it. LEDs usually
produce red light, but today’s LEDs can produce RGB (Red, Green and Blue)
light, and white light as well.
3-D Monitor
It is a television that conveys depth
perception to the viewer. 3-D describes an image that provides the perception
of length. When 3-D images are made interactive then user feels involved with
the scene and this experience is called virtual reality.
Thin Film Transistor (TFT)
TFT and Active-Matrix LCD (AMLCD)
is a Liquid Crystal Display (LCD). With active-matrix displays, each pixel is
controlled by one to four transistors that can make the screen faster,
brighter, more colorful than passive-matrix and capable of being viewed at
different angles. Because of this improved technology, active-matrix screens
are often more expensive.
Printers
A printer prints
information and data from the computer onto a paper. It can print documents in
color as well as in black and white. The quality of a printer is determined by
the clarity of a print. The speed of a printer is measured in Characters Per
Second (CPS), Lines Per Minute (LPM) and Pages Per Minute (PPM). Printer
resolution is a numerical measure of print quality that is measured in Dots Per
Inch (DPI). Printers are divided into two basic categories
- Impact Printers: This type of printer strikes paper and ribbon together to form a character, like a typewriter. Impact printer can print a character or an entire line at a time. They use pins or hammers that pressed an inked ribbon against the paper. They are less expensive, fast and can make multiple copies with multipart paper. There are four types of impact printer
- Dot Matrix Printer: It forms characters using rows of pins which impact the ribbon on top of the paper therefore also called pin printers. Dot matrix printers print one character at a time. It prints characters and images as a pattern of dots. Many dot matrix printers are bi-directional, that is they can print the characters from either direction, i.e. left or right.
- Daisy Wheel Printer: In daisy wheel printers, characters are fully formed on the petals, like typewriter keys. These printers produce high resolution output and are more reliable than dot matrix.
- Line Printer: It is a high-speed printer capable of printing an entire line of text at once instead of one or more characters at a time. These are impact shaped character printers which print one line at a time. Print quality of line printer is not high.
- Drum Printer: An old line printer technology that uses formed character images around a cylindrical drum as its printing mechanism. When the desired character for the selected position rotated around the hammer line, the hammer hit the paper from behind and pushed it into the ribbon and onto the character.
- Non-Impact Printer: This type of printer uses electrostatic chemicals and inkjet technologies. They do not hit or impact a ribbon to print. It can produce high quality graphics and often a wide variety of fonts than impact printers. There are following types of non-impact printer
- Inkjet Printer: It is a printer that places extremely small droplets of ink onto paper to create an image. It sprays ink onto paper to form characters and prints high quality text and graphics.
- Thermal Printer: It uses heat on chemically treated paper to form characters. Fax machines that use rolls of paper are also of thermal printers type. It is relatively slow, expensive and requires special paper.
- Laser Printer: It provides the highest quality text and images for personal computer. They can print in different fonts that is, type styles and sizes. Laser printer uses laser beam onto photo sensitive surface for printing. It prints high quality graphics and more expensive than impact printers.
- Electromagnetic Printer: Electrographic or electro-photographic printers are very fast printers and they fall under the category of page printers. The electrographic technology have developed from the paper copier technology.
- Electrostatic Printer: These printers are generally used for large format printing. They are favoured by large printing shops because of their ability to print fast and making low cost.
Plotter
It is an output device that uses a pen,
pencil, marker or other writing tools for making vector graphics. A plotter is
a special kind of output channel like a printer, that produces images on paper.
They are mainly used to produce large drawings or images such as construction
plans, blueprints for mechanical objects, AUTOCAD, CAD/CAM, etc. Plotters
usually come in two designs as follows
- Flat Bed Plotter: These plotters are of small size to be kept on table with restriction of paper size.
- Drum Plotter: These plotters are of big size using rolls of paper of unlimited length.
Speaker
It is an output device that receives sound in the form of electric current. It needs a sound card connected to a CPU, that generates sound via a card These are used for listening music, for being audible in seminars during presentations, etc. Computer speakers are the speakers which are attached internally or externally to a computer system.
Headphones
These are a pair of small loudspeakers or less commonly a single speaker, held close to a user’s ears and connected to a signal source such as an audio amplifier, radio, CD player or portable media player. They are also known as stereo phones, headsets or cans.
Projector
It is an output device which is used to project information from a computer onto a large screen, so it can be viewed by a large group of people simultaneously. Projectors are widely used for classroom training or conference holes with a large audience. It provides a temporary output display. There are mainly two types of projectors; LCD projector and DLP projector.
Both Input-Output Devices
Few devices that give input and also show or get the output through same device. These are as follows,
- Modems
- Network cards
- Touch screen
- Headsets (headset consists of speakers and microphone in which speaker acts as output device and microphone acts as input device).
- Facsimile (FAX) (it has scanner to scan the document and also have printer to print the document).
- Audio cards/sound cards.
Input/Output (I/O)Port
- Parallel Port: It is an interface for connecting eight or more data wires. The data flows through the eight wires simultaneously. They can transmit eight bits of data in parallel. As result, parallel ports provide high speed data transmission. Parallel port is used to connect printer to the computer.
- Serial Port: It transmits one bit of data through a single wire. Since, data is transmitted serially as single bit. It provides slow speed data transmission. It is used to connect external modems, plotters, barcode reader, etc.
- Universal Serial Bus (USB): It is a common and popular external port available with computers. Normally, two to four USB ports are provided on a PC. USB also has the plug and play feature, which allows devices ready to be run.
- Firewire: It is used to connect audio and video multimedia devices like video camera. Firewire is an expensive technology used for large data movement. Hard disk drive and new DVD drives connect through firewire. It has data transfer rate of upto 400 MB/sec.
MP3 is an audio coding format for digital audio which uses a form of lossy data compression.
The I/O devices that are attached, externally to the computer machine are also called peripheral devices. These are hardware.
Speech recognition software can interpret voice data into words that can be understood by the computer.
A dumb terminal is simply an output device that accepts data from the CPU.
