Chp06_inputouputdevices

By. Shafiq A chachar 1

INPUT AND OUTPUT DEVICES

Chapter 03


Definition of Input DevicesEquipment that supplies data and programs to the computer.An input device is a peripheral device that converts symbols that people understand into bits that computers can process.An input device includes a keyboard, a terminal, a touch screen, a mouse, a scanner, etc.


KeyboardsA keyboard is a device used to encode data by key depression, which enters information into a system.The keyboard converts alphabets and numbers, and other special symbols into electrical signals that processor can understand and process. These signals are sent to the computer's CPU.


KeyboardsThe keyboard is divided into four groupsAlphanumeric keypad: This is main part of the keyboard. By using this keypad the letters a-z, A-Z, numbers 0-9, and special characters like ! @ # $ % ^ & * ( ) _ + | \ = - ] [ { } ’ ; : ” / . , < > ? ` ~ may be typed.Numeric keypad: It is located on the right side of keyboard.


Keyboards

Function keypadA set of twelve keys (F1 to F12). All of these keys have predefined meanings which depends on the application software.

Special Function keypad: When “Num Lock” is turned on, the keys on Numeric Keypad such as arrows, Home, End, PgUp, PgDn and Del are disabled.


KeyboardsThere are three different layouts.QWERTY: This is a standard keyboard layout. QWERTY indicates the arrangement of the upper left corner six letters in the first row of the alphabetic keys.AZERTY: This is a keyboard layout that is similar to the QWERTY layout and some European countries use this keyboard.Dvorak: This is another keyboard layout modified greatly from a standard layout. The keyboard is devised to increase typing speed by placing frequently used keys more naturally.


TerminalsA terminal is an input/output device that usually includes a keyboard for input, a video display for output, and a communications link to send and receive information. There are three different types:Dumb Terminal: This is an input/output terminal that does not have a capability of processing. It only enters and receives data without processing.


TerminalsSmart Terminal: This terminal has some processing capability. It has a small memory. It performs some editing of data before sending them to a main computer.Intelligent Terminal: This is a terminal that has a full processing capability. It has a processing unit, primary storage. Recently, most intelligent terminals have local disk. It is actually a microcomputer with communications capability.


Pointing Devices


What are Pointing Devices

A piece of equipment that moves onscreen such as an arrow, cursor, or insertion point.

The pointing device determines the repositions the onscreen pointer by determining position, distance and speed of the pointing device.


MouseAn object used as a pointing and drawing device.It usually has a ball and buttons and is connected to the system unit through serial port.As a mouse is rolled across the flat desktop in any direction, it locates the pointer correspondingly on the screen. Then it issues commands using the selection buttons on the mouse.Many portable microcomputers such as lap-tops use trackballs instead of mice.


Light PenA light pen is a light-sensitive pen-like device used by pointing it at the display surface.A user brings the light pen to the desired point on the screen and presses a button, causing it to identify the current location. It is used to select options from a menu or to draw images.The light pen doesn't require a special screen or screen coating, as does a touch screen, but its disadvantage is that holding the pen up for an extended length of time is tiring to the user.


Touch ScreenA touch screen is a monitor screen that allows users to interact with a computer system by touching an area of the display screen.The screen is covered with a clear plastic layer that has a matrix of cells. A user touches a graphic button that displays option on the screen. Touch screens are easy to use. Thus, many kiosks use touch screens as input forms.


JoystickIt is usually used for playing computer games.It usually has a square or rectangular plastic base to which is attached a vertical stem. Control buttons are located on the base and sometimes on top of the stem. The stem can be moved in all directions to control the movement of an object on the screen. The buttons activate various software features, generally producing on-screen events.


TrackballA trackball consists of a ball resting on two rollers at right angles to each other, which translate the ball's motion into vertical and horizontal movement on the screen.A trackball typically has one or more buttons to initiate other actions.A trackball is useful for fine work because the user can exert fingertip control; a mouse is better for bold moves, such as those used with a graphical user interface.


Digitizer TabletA digitizer tablet is also called a graphics tablet or just a digitizer. The digitizer is a drawing tablet used to sketch new images or trace old drawing or photograph. The user uses a pen-like device called stylus or cursor to draw images.Designers and architects usually use digitizers.Light pen and digitizer technologies are used for pen-based computing.


Crosshair CursorAn input device that you move over hard-copy images of maps and drawings to enter them into computer storage.It is also known as Puck.It is a mouse-like device with buttons for selecting items or choosing commands and a clear plastic section extending from one end with cross hairs printed on it.The intersection of the cross hairs on the puck points to a location on the graphics tablet, which in turn is mapped to a specific location on the screen.


Source Data Automation


DefinitionThe process of collecting data in digital form.This procedure has resulted in saving of thousand of hours of wasteful and duplicated effort.It speeds up inventory taking at supermarkets, quality control operations in factories, and check processing in banks.


Optical Character Recognition (OCR)The use of reflected light to input marks, characters, or codes.The optical reader shines light on the characters and the reflection of the character is compared with a stored reference of characters.Optical Fonts have the advantage of being readable by both computers & human beings.

Optical characters are widely usedIn processing turnaround documents, such as the credit card slips used for customer transaction in stores and restaurants.

for public utilities’ remittance advice slips e.g., by the gas and electricity boards.

hire-purchase companies who issue a book of payment vouchers encoded with the borrower’s code number and amount.Each voucher is returned with the payment so that the borrower’s account is correctly updated.


Optical CharacterRecognition (OCR)

Advantages of OCR1. Input is both human and machine readable.2. No labor-intensive keyboard preparation.

Disadvantages of OCR1. Form design, stationery and printing costs

are high.2. The specialist hardware and software

required can be expensive.


Optical Mark Reader (OMR)Standard pre-printed documents are used on which horizontal marks are made with a black marker (pencil, ball-point pen, typewriter) in predetermined positions.The positioning of each mark is determined by dividing the form into areas or boxes printed in a distinctive color.

OMR is used bySome utility companies, such as the gas and electricity boards for meter reading purposes. Each numeric digit on the electricity meter is represented by a mark on the form.Certain educational establishments use to evaluate multiple-choice examination papers


Optical Mark Reader (OMR)

Advantages of OMRIt is simple and cheap to use.

Data is captured without labor intensive keyboarding and verifications.

Disadvantages of OMRAlphabetic characters cannot be easily identified.


Optical CodesThe most widely used type of optical code is the bar code.Bar codes are represented in the form of optical bars. Two bars normally represent each digit in the code. The spacing and the thickness of each bar identify the digit.The code is read by using a gun, scanner or wand which is hand held or by passing the bar code over a static reader.


A complex coding system relates the pattern of widths of the dark and light bars to the number they represent. The widely used EAN bar codes represent 13-digit numbers. The pattern can be “read” rapidly by a laser scanner. The number obtained can be used to retrieve such information about the product as its nature, type and cost. The number also appears in ordinary human-readable form beneath the bar code.

Bar Code


Optical CodesThe bar code is written onto a data carrier, which may be a ticket, tag, label or plastic card and is then attached to the product.Bar coding systems allow for stock control and re-ordering. They also provide detailed information about ‘buying habit’ which can then be used for strategic planning and marketing.Book shops and libraries also use bar coding systems.Dot matrix printers can print bar codes. Some supermarkets also have electronic scales that can print bar coded labels for attachment to fresh produce.Two types of bar coding systems: the American Uniform Product Code (UPC); and the European Article Number (EAN).


Point of Sale SystemA point-of-sale system is a generic term for various types of device used in retailing.At their simplest they consist of cash registers which store data in computer sensible form. They also print a customer receipt, security log, and display the details of each transaction, the change required, and a total.POS systems are widely used in chains of supermarkets or cash and carry warehouses which need regular information on stock levels and takings. Special purpose keyboards have been designed for use in some outlets.


Point of Sale SystemData can be entered via a keyboard or by a sensor or pen reader reading a bar-coded label.Advantages of system include:

speed of processingavailability of sales informationthe ability to update prices quickly


Image ScannersA image scanner is a device that reads spatial pattern such as images, graphics and texts, and then generates digital signals of that pattern.Converted digital data may be processed by a computer, stored in a disk, printed by a printer or displayed on a monitor.Image scanners are commonly used to capture graphic images that can then be placed in a page or on any document.Scanners which include optical character recognition (OCR) software are called intelligent image scanners. Because it enables test editing through a word processing package.Dumb scanners cannot recognize any of the text they read.


A banking-industry technology that processes checks by sensing special characters in a magnetic ink.There are two technologies in magnetic data entry.

A magnetic ink character recognition (MICR) technologyA magnetic stripe technology

A magnetic ink character recognition (MICR) technology reads iron oxide ink preprinted or encoded on checks, deposit slips or on documents. An MICR reader electronically captures data, by first magnetizing the magnetic ink characters and then sensing the signal

Magnetic Ink Character Recognition (MICR)


Voice input devices are also called speech- recognition devices or voice-recognition systems.This device converts a user's speech into a digital code.Spoken words are first digitized and then matched against a dictionary of patterns previously stored in the computer.

Speaker-dependent systems should be trained by taking actual user's word sample before using, but speaker-independent systems can recognize only limited vocabularies.The advantage of the voice-input systems is that they enable users to keep their hands free for other tasks.

Voice Input Devices


Smart CardSmart Card has a plastic strip with some integral memory and processing capacity.It is also known as an “intelligent card”.The credit card is not a smart card, as it is only equipped with a magnetic strip which stores information. It cannot be readily reprogrammed, and it can only interact with other computers in a simple way.The smart card is far more advanced. It can be used as an electronic purse or a multifunction security pass.This is because it is, in effect, a computer. It is capable of all the basic computer functions: retaining information (such as personal details, security privileges, credit levels); processing (such as calculating cash balances); and communicating with other computers.


Output Devices

Output Devices

Softcopy OutputDevices

Hardcopy Output Devices


Definition of Output DeviceAn output device is any peripheral device that converts machine-readable information into people-readable form.

For example, monitor, printer, plotter, voice output device, speakers, film recorders, computer output on microfilm etc.


Softcopy Output DevicesDisplay Devices

An output device that contains a viewing screen.Two categories of display devices

Monitor, a display device without a keyboard.Display terminal, a communication workstation that includes a screen and an attached keyboard.

Most common screen sizes are 14, 15, 17 inches – measured diagonally along the screen surface.


ResolutionA computer display is also called a display screen or video display terminal (VDT).Images are represented on monitors by individual dots called pixels.A pixel (picture elements) is the smallest unit on the screen that can be turned on and off or made different shades.The density of the dots determines the clarity of the images, the resolution.The screen resolution is usually expressed as the number of columns by the number rows. A 1024x768 resolution means that it has 1024 columns and 768 rows.Another measure of display resolution is a dot pitch. A display’s dot pitch indicates the distance between pixels in millimeters.Many displays have a dot pitch of 0.26 or 0.28. A smaller dot pitch produces better resolution.


Color DisplaysMost monitors are of red-green-blue (RGB) type.An RGB monitor forms all colors on the screen by mixing combinations of only these three colors.Most monitors sold today produce non-interlaced images.A non-interlaced technology that is developed later refreshes all the lines on the screen form top to bottom.The non-interlaced method gives more stable video display than interlaced method.It also requires twice as much signal information as interlaced technology.An interlaced technique refreshes the lines of the screen by exposing all odd lines first then all even lines next. Televisions use interlace technology.Interlace monitor cost less than non-interlaced monitor.There are two forms of display: cathode-ray tubes (CRTs) and flat-panel display.


CRT & Flat Panel DisplayA CRT (cathode-ray tube) is a vacuum tube used as a display screen for a computer output device. Although the CRT means only a tube, it usually refers to all monitors.CRTs have become very inexpensive and have excellent color output, but are bulky and fragile and consume a great deal of power.Display device which form image by manipulating charged chemicals or gases sandwiched between panes of glass are called flat-panel displays.Flat-panel displays use liquid crystal display (LCD) technology.LCD displays light up charged liquid crystals, special color filters to paint the screen.


CRT & Flat Panel DisplayLCDs compared to CRTs consume low power, do not emit any electromagnetic radiation, are portable and compact in size, but costs more and the screen provides less contrast with more glare and poor resolution. In order to improve resolution backlit LCDs are used for the purpose now.


Graphics StandardsBit mapping allows software to control each pixel on the screen as an individual element. The computer can create virtually any type of image on the screen.A monochrome monitor has two colors, one for foreground and the other for background. The colors can be white, amber or green on a dark (black) background. The monochrome monitors display both text and graphics modes.A color monitor is a display peripheral that displays more than two colors.Color Graphics Adapter (CGA)

It is a circuit board introduced by IBM and the first graphics standard for the IBM PC. With a CGA monitor, it is harder to read than with a monochrome monitor, because the CGA (320 x 200) has much fewer pixels than the monochrome monitor (640 x 350).It supports 4 colors.


Color MonitorsEnhanced Graphics Adapter ( EGA)

Resolution of 640 by 350 pixels.Supports 16 colors.

Video Graphics Array (VGA)Provides medium to high resolution.In a text mode, resolution = 720 by 400 pixels.16 colors with resolution of 640 by 480 pixels & 256 colors with 320 by 200 pixels.

Super VGA can support a 16.8 million colors at 800 by 600 pixels and 256 colors at 1024 by 768 pixels. A high-priced super VGA allows 1280 by 1024 pixels.Larger monitors (17" or 21" & larger) with resolution of 1600 by 1280 pixels are available.VESA (Video Electronics Standards Association) has set a standard for SVGA.


Drawbacks of High ResolutionSpeed – because there is more information to

paint on a high resolution screen, the screen

takes longer to rewrite every time it is

changed.

Memory – More memory is required.


Hardcopy Output Devices Printers


Definition of a Printer

A printer is an output device that produces a hard copy of data.

The resolution of printer output is expressed as dots per inch (dpi). The higher the dpi, the harder it is to tell that dots were used to compose the image.


Types of Printers

Impact PrintersHammer hits ribbons, papers or print head.

Example, Dot-matrix & daisy-wheel printers

Nonimpact PrintersThey do not have the hammer & do not hit.

An example is an ink-jet and laser printer.

Types Of Printers

Impact Printer Non_Impact Printers


Small Computer SystemsDot-Matrix printersInkjet-PrintersLaser PrintersSolid-Ink Printers

Dot Matrix Printer prints characters and form graphic images using one or two columns of tiny dots on a print head.The dot hammer moves serially across the paper strikes an inked-ribbon and creates images on paperThey are highly reliable and inexpensive. They are used where a high-quality image is not essential.Kinds of dot matrix printers (7, 9, 18, or 24 pins).


Ink-Jet PrinterA printer that sprays one or more color of ink at high speed onto the paper and produces high-quality printing. This printer also produces color printing as well as high-quality image.Ink-jet printers can be used for variety of color printing at a relatively low cost.

Laser PrinterA printer that uses the electrophotograpic method used in a Photocopier.The printer uses a laser beam light source to create images on a photographic drum. Then the images on the drum are treated with a magnetically charged toner and then are transferred onto a paper. A heat source is usually applied to make the images adhere.In 1984, Hewlett-Packard introduced the first desktop laser printer, called the LaserJet.


Laser PrinterBecause of their speed and output quality, laser printers are by far the most popular type of printer for business applications.Common speeds = 4, 6, 8 and 12 ppm.Resolution = 300 to 600 dpi.Many laser printers come with 4 MB of RAM.Although a high-priced color laser printer is also available in the market, a less expensive, desktop gray scale laser printer is widely used


Large Computer SystemsLine Printers

A high speed printer that use impact method to produce a line at a time printer output.They normally print 80 to 132 characters, therefore these printers have 80 to 132 printing heads for each character.From 300 to over 3000 lines can be printed each minute.Three types: chain, band & drum printers.


Page PrintersA high-speed printer that generates a full page output at a time.For offices, the most common type is network laser printer.They work much faster at a rate of anywhere from 12 to 40 ppm.Many can collate and staple, as well.Page Printers for midrange & mainframe computers can print up to a few hundred ppm.They can produce output on both sides of the paper. Page printers offer considerable savings over line printers, because they do not require human intervention to switch paper and printing elements


Other Output Equipment

SpeakersPlotterVoice Output Devices

SpeakersOutput devices that produce sound.Cases on speakers are shielded to prevent magnetic interference.They are commonly used in video demonstrations and presentations as well as video conferencing.In desktop system unit, sound card is required to play sound through speakers or headphones.Portable computers use PC cards to gain sound card capabilities.


PlottersA plotter is a special-purpose output device that draws images with ink pens. That is, the plotter is a graphics printer for making sophisticated graphs, charts, maps, and three-dimensional graphics as well as high-quality colored documents. It can also produce larger size of documents.Plotters require data in a vector graphics format that can produce images with a series of lines.There are two main types of plotters:Ink-Jet Plotter

This is a plotter that has a drum. A paper wraps the drum that rotates to produce plots. Pens in a drum plotter move across the paper while the drum is turning. A drum plotter is usually used to produce smaller drawings.They are slow, low in cost and save space on the desktop.


Plotters

Electrostatic Plotter (Table Plotter)It creates images with a toner bed similar to that of a photocopying machine. It uses a matrix of tiny wires to charge the paper with electricity. When the charged paper passes over the toner bed, the toner adheres to it and produces an image. It is widely used for producing large drawings.It is faster and expensive than ink-jet plotter.


Computer Output MicrofilmA system for reducing computer output to microscopic form and storing it on photosensitive film.The microfilm can be in the form of Reel, Strip, and Microfiche.A 4 x 6 inch microfiche card = 270 printed pages.For example in motor trade: price lists of spare parts are supplied to dealers on microfiche.Advantages

Stationery costs are reduced: reproductions made from a master microfiche are quite inexpensive.Transport is simple and cheap.Retrieval of information is easier: a reel of film can be coded and automatic search facility provided in the viewer.

DisadvantagesSpecial equipment is need to view the film and to provide a full size hard copy is required.COM equipment is expensive.Microfilm can only be used internally because of the need to provide viewers

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