Input Devices Notes

August 28, 2018 | Author: pmaina | Category: Computer Keyboard, Image Scanner, Optical Character Recognition, Barcode, Touchscreen
Share Embed Donate

Short Description

computer systems input devices...


COMPUTER SYSTEMS softwar e and live-ware all working together in A Computer system is a collection of computer hardware, software data inputting, processing and production of required output from a computer. There a computer system consists of three functional elements, that is:i.  the physical/tangible components that make up the computer system Hardware –  the Software  –  the ii.  the programs instructions that enable computer c omputer to perform its functions. iii.  (people-ware) –  these  these are the computer users, that is people who coordinate the various Live-ware (people-ware) –  activities which are necessary to make a computer system perform useful tasks e.g. data entry clerks, computer operators, programmers, system analysts, administrators etc Basically a System is a collection collect ion of independent entities that collectively work together to achieve a desired goal. Basically, a computer is made up of two main components, namely hardware and software. However a computer cannot work on its own without human intervention hence the term computer system. A computer system is a collection collecti on of three components namely hardware, software and liveware that work together to receive, process, manage and present information in a meaningful format. • Hardware are physical or tangible components that make up a computer. oftware refers to sets of instructions that direct a computer on what to do. They are mainly clas sified into • S oftware two categories namely system namely system software and application software. t he computer to • Liveware refers to the human being. It is the user who dictates what task he/she wants the  perform. However, in this chapter, emphasis is on the hardware hardware and software components. In this book, more emphasis has been placed on the first two, i.e. hardware and software. Computer hardware Computer hardware is classified into four categories namely input devices, central processing unit, output devices and storage and storage devices. INPUT DEVICES Input devices convert user input which is in human language form into machine language that a computer can process. Thus the main functions of input devices includes:- Accepts data and instructions from the computer user to relay it into computer memory and CPU for  processing. - Converts (codes) data input into a form that the c omputer can understand, that is machine readable form. Input devices can be classified according to the methods they use to enter data namely: keying   , pointing, scann i ng devices devices,, voice r ecogni ti on and other technologies used to capture data. Different types of input devices transmit different types of data or transmit data in different ways. A. KEYING DEVICES Keying or typing is the most common way to input data. A keying device converts typed numbers, letters and special characters into machine readable form before processing takes place. Some common types of keying devices include: 1. Keyboard A computer keyboard is an input device that contains keys that all ow you to type letters of the alphabet, numbers, spaces, punctuation marks, symbols and other basic characters. A computer ke yboard also contains special keys that allow you to perform specific functions on the computer. Characteristics Characteristics of a keyboard a numeric keypad designed to make it easier to enter numbers,   function keys programmed to issue commands and accomplish certain tasks, arrow keys and other cursor-control keys (e.g., home, end, page up, and page down) that controls the  insertion point (Cursor - a symbol on the screen that indicates where the next typed character will display), and  Toggle keys that can be switched between two different states. status lights that indicate modes that can be turned on and off by toggle keys (e.g., caps lock and num  lock)


special keys such as esc, shift, ctrl, and alt that have varying functions depending on the software Types of keyboards A standard computer keyboard  sometimes is called a QWERTY keyboard because of the layout of its  typing area.  An enhanced keyboard  has 12 function keys along the top row, 2 ctrl keys, 2 alt keys, and a set of arrow and additional keys between the typing area and the numeric keypad.  Cordless keyboards transmit data via infrared light waves.  Keyboards for notebook and handheld computers usually have smaller and fewer keys than desktop computers. A portable (flexible) keyboard  is a full-sized keyboard you can attach to and remove from a handheld  computer. It is a more portable type of keyboard that can be folded and packed into a bag. 2. Ergonomic keyboard - An ergonomic keyboard is specially designed to provide comfort and alleviate wrist strain. 3. Keypad - A keypad is a miniature keyboard used on portable devices such as PDAs, laptops and mobile  phones. 4. Br ail le keyboard - Braille keyboard is an accessibility option for the blind. It consists of keys identified  by raised dots. ; Advan tages of K eyboards  

The keyboard is very reliable compared to other methods of text input such as voice input or optical character recognition which are prone to error. The keyboard is vrcstef1tective, since every computer comes with a keyboard and there is no additional cost involved.

B. POINTING DEVICES A pointing device is an input device that allows you to control the pointer on the screen and are mostly used on computers running graphical user interface (GUI) operating systems such as Microsoft Windows. In a graphical user interface, the pointer is a small symbol on the screen. Common pointing devices include the mouse, trackball, touchpad, joystick, touch screen, light pen, and a stylus. 1. Mouse A mouse is a pointing device, designed to fit comfortably under the palm of your hand that is moved across a flat surface allows you to move the pointer on the screen. You also can make choices and initiate  processing on the computer by using a mouse buttons. How a mouse works As you move a mouse across a flat surface, the movement is translated into signals t hat are sent to the computer, and the pointer on the screen also moves. When you move the mouse to the right, the pointer moves to the right on the screen. For Windows users, the top of a mouse has at least two buttons and sometimes also a wheel. Generally, you use a mouse to move the pointer on the screen to an object and then  press a button, or click, to perform a certain action on that object. Other operations you can perform using a mouse include right-click, double-click, drag, right-drag, rotate wheel, and press wheel button. Uses of a Mouse - The mouse is used to select options from or from a s et of icons (simple graphic images) by clicking the mouse button. - To position the cursor when editing text or using a design package, - To select an object in a drawing or a piece of text to be copied, moved or deleted. Different types of mice i. A mechanical mouse has a rubber or metal ball on its underside, two buttons and may have an optional scroll wheel. When the ball rolls in a certain direction, electronic circuits in the mouse translate the movement into signals that are sent to the computer. For better traction, you should  place a mechanical mouse on a mouse pad. ii. An optical mouse has no moving parts; instead it uses uses light emitting diode (LED), an optical sensor and digital signal processing (DSP) in place of the traditional mouse ball and


electromechanical transducer to detect the mouse’s movement. An optical mouse can be used on nearly all surfaces, is more precise than a mechanical mouse, and does not r equire cleaning. iii. A cordless mouse, or wireless mouse, is a battery powered mouse that transmits data using wireless technology, such as radio waves or infrared light waves. Thus does not require physicall y to be connected to the system unit. Advantages of using a mouse instead of a keyboard - The mouse is easy & convenient to use. - Most Modern software includes an option to use it. - It selects a position on screen much more quickly than a keyboard. - It is inexpensive. Disadvantages of Using a Mouse - The mouse cannot be used to input text easily thus you still need a keyboard to do that. - It is relatively slow for selecting menu options. A user who is familiar with the ke yboard commands can select the options more quickly. - It is not very accurate for drawing purposes. - The rnouse requires flat surface too operate. 2. Trackball A trackball is a stationary pointing device that works just like a mouse only that its ball is located at the top and Instead of moving the device on a flat surface, the user instead rotates the ball using a finger. Some computer keyboards come with an integrated trackball hence no need for a mouse. : The tracker ball does not require a flat surface to operate. Advantage  3. Joystick A joystick is a specialized hand-held pointing device used for playing games. A joystick has a vertical lever mounted on a base. The user controls game actions by var ying the pressure, speed and direction of the joystick. The joystick usually has buttons used to issue commands or trigger actions once the cursor is in the right place. Some give more control on the screen by rotating the stick as well. Advantages

- It allows the fast interaction needed in games. - The lever can be moved in any direction from its z ero position. 4. Light pen A light pen is a handheld light-sensitive pen-like pointing device. The light-pen is used to select a point on the screen. It is sensitive to the presence and absence of light through a light sensitive cell at its end. It operates by identifying a pixel on the screen hence pointing to the current location. Uses of L i ght Pens

- Light pens are usually used as design aids. The light pen is used to indicate which shapes to draw, where they should be drawn on screen and the size. - Light pens are also used to read bar codes and to indicate a point on a screen or pad, e.g. for selecting options for drawing. (An alternative to this is a touch-scr een, where a finger is used to point instead of a pen). Advantages of a light pen as an input device, - Light pens provide a direct mode of input. - It is a faster input device because it involves just pointing on the screen and selecting options. - They are more precise than using a mouse. - Can be used to draw images on the screen. - It is light and easily portable (saves energy). - A light pen will result in few errors. Disadvantages of Light Pens - Can only detect the presence and absence of light. - Can only be used in conjunction with a graphic VDU, which is able to sense light shining on the screen using special hardware and software. 5. A stylus


A stylus on the other hand is used on touch sensitive devices such as PDA screens that recognize a handwritten text. A stylus looks like a ballpoint pen but uses pressure, instead of ink, to write text and draw lines. An electronic pen can be used on a graphics tablet, which consists of a flat, rectangular, electronic plastic  board used to input graphical data. 6. Touch screen A touch screen is a touch-sensitive display on the screen through which data can be entered into a computer just by touching it with a finger in order to select an item. Items are selected just as they would  be with a mouse pointer or light pen. The screen consists of infrared light crisscrossing behind it. When the user touches a location on the screen, the finger interrupts the infrared light and the command touched is executed. A touchpad is a flat, rectangular pointing device that is sensitive to pressure and motion. Uses of Tou ch Screen

Touch screens are used in places where ke yboards would be prone to damage due to the environment, or there is little space for the keyboard. For example, bars and fast food places would use touch screens. The screens can be positioned so that they are out of the way of spillage, but easily accessible to the  person serving. The touch would be linked to a microcomputer in an office nearby, which would record the sales and update stock. The touch screen can display a series of menus and displays through which options can be selected. When the items are sold, the computer adds up the bill and updates the accounts/stock. Advantages of Tou ch Screen 

-  No extra peripherals are needed except the monitor, although the monitor must be adapted to respond to touch. - Effective where a keyboard or mouse would get wet or dirty. A screen c an be positioned out of the way of the work area. - It is useful for people who work when standing and moving about. Di sadvantages of T ouch Scr een


It is not useful for office use, because it is tiring to keep reaching to touch screen. It is unsuitable for inputting large quantities of dat a, since selecting screen options can only input relatively few data.

C. SCANNING DEVICES A scanner is a light-sensing input device that reads printed text and graphics and then translates the results into a form a computer can use. Scanning means capturing data from an object and converting it into digital format, for further processing or incorporating it into other documents. There are two types of scanners namely optical, and magnetic scanners. Also can be classified as either hand-held or flat bed scanners. Hand-held scanners: They are moved manually by hand across the page being scanned. -Usually they are cheap and portable, but not very accurate and consistent for picture or image capture. Flat-bed scanners:  Flat-bed scanners move across the page or roll the page through the scanner mechanically. The document is laid flat and the scanner remains stationary on a table while the document is scanned. -A flat-bed scanner is accurate and consistent. Optical scanners Optical scanners capture data using optical or light technology. A light beam passes over an object, and the image is analyzed by specialised software. Examples of optical scanners include: i. Optical mar k r ecogniti on

Optical mark recognition (OMR) devices detect/read marks made on a piece of paper using ink or a soft pencil, by passing an infrared beam of light over them. The position of the mark relative to a fixed  point of reference is analyzed to determine whether it is in the required place. Types of codes on Documents include:  Marks - Short lines made by hand, usually in pencil on a document. 4

Characters - Hand-written e.g. on meter-reading, printed, e.g. in magnetic ink on cheques.  Printed lines The most common of these is the bar code. Uses of OM R 


Multiple-choice examination papers or aptitude test. Insurance premium collection by insurance companies. Supermarkets for stock recording. Traffic surveys. Voters’ registration process. Used in banks to verify a customer’s signatures against the one stored in the computer. Used for IQ tests and lotto tickets It is also used on school attendance registers and surveys.

Advantages of OM R

- Fewer mistakes are made by machines reading marks than are made when reading hand-written characters. - Data can be prepared without any special equipment. - Data can be prepared where it is collected, e.g. students sitting for a multiple choice exam mark the answers themselves on the answer sheet provided, or market researchers can mark questionnaires while asking people questions on the street. - OMR can eliminate transcription errors provided the instructions given to users are clear. - OMR is useful when a high amount of forms to be processed is r equired in a short time. Di sadvantages of OM R

- It is difficult for a computer to check marked data, i.e. verification of the data is difficult. - Documents may be difficult to understand and fill or impractical to design. For example, if a document has several values the format has to have a different box to mark for each possible value. - The person putting the marks on the document has to follow the instructions precisely. - The document reader has to be reprogrammed for each new document design. - Document for mark reader are complicated to design. - Input of the data to computer is slow. - Very expensive to design forms and implement OMR ii. Optical B ar r ecogniti on The optical bar code (OBR) scanners are used to c apture data coded as lines of varying thickness known as bar codes or Universal Product Code (UPC). Bar codes are most common on consumer  products and contain information such as country of manufacture, manufacturer and the product code. Bar codes do not have the price details because prices vary from one place to another. The two common types of bar code scanners are the hand held wand and desktop bar code reader. Barcode Reader A barcode reader is a hand-held or stationary input device used to capture and read data contained in a  bar code. The data must be sent to a computer so that a software application can  process it. A barcode reader works by directing a beam of light across the bar code and measuring the amount of light that is reflected back. (The dark bars on a barcode reflect less light than the white spaces between them.) The scanner converts the light energy into electrical energy, which is then converted into data by the decoder and forwarded to a computer.  A barcode is simply a numeric code represented as a series of thick and thin black lines, with numbers underneath for humans to read. Uses of barcode readers - Mostly used in shops and supermarkets for products The most common use of barcode readers is at Point-of-Sale (POS) in a supermarket. The code for each item to be purchased needs to be entered into the computer. Advantages:

- Fast-selling items can be identified quickly and automatically reordered to meet consumer demand, - Slow-selling items can be identified, preventing a build-up of unwanted stock,


- The effects of repositioning a given product within a store can be monitored, allowing fast-moving more  profitable items to occupy the best space, - Historical data can be used to predict seasonal fluctuations very accurately. - Items may be re-priced on the shelf to reflect both sale prices and price increases. - This technology also enables the profiling of individual consumers, typically through a voluntary registration of discount cards. While pitched as a benefit to the consumer, this practice is considered to be potentially dangerous by privacy advocates. - Reading the barcode is far quicker and more accurate than typing in each code using a keypad. Barcode can be found on many other items that have numeric codes which have to be read quickly and accurately - for example ID cards. - If the code becomes damaged or mis-formed it may not be read

iii. Optical character recogniti on An optical character recognition (OCR) is a technology that is used reads typewritten, computer  printed, or handwritten characters from ordinary documents and translates the images into a soft copy that can be manipulated using a word processor. Most OCR document readers reco gnise at least one of two fonts, but as software improves, OCR readers and scanners can recognise a greater range of fonts, and printed documents can be used a source documents. Today an OCR comes as integrated feature of more advanced scanners called flat-bed scanners. Flat bed scanners are used to capture  pictures and real objects. Uses of OCR 

Turnaround documents  –  it’s popularly  used to process turnaround documents. turnaround documents are documents produced as output and which can be re-used as input by the computer. For example, a printed electricity bill with billing information is reused to capture details and input  payment details. - Sales Order forms —  these can be printed by the computer with standard data, e.g. stock codes, account code. The salesman then enters details of the order form and returns it for OCR processing. - Stocktaking sheets —  the computer can print out stock sheets in OCR characters and the stock checkers enter actual stock quantities on the form in careful handwriting. The sheet can then be optically read into the computer for amending the stock records. Advantages

-  No typing or transcription requirements and therefore not prone to transcription errors. The documents are turned around thus saving on stationery. - It is understood by humans and computers- The contents of the documents are both human and machine sensible, and can therefore be read and checked b y people. - Provides a faster input as compared to typing. - Documents for OCR do not have to be designed as precisely for OMR. Disadvantages

- It’s expensive method of input because specialised techniques and equipment required. - Handling precaution necessary, e.g. the document should not be folded or creased for accurate reading. Good paper quality is therefore crucial to minimize creasing. - Document size and type area may be limited for a ccurate reading. Special typing and characterformation are important, since OCR systems cannot recognise some characters, particularly handwritten or in unusual fonts. -  Not always 100% accurate and requires proof reading before saved and confirmed. - Human handwriting is rarely accurately recognizable by OCR, the computer might confuse different shapes like '5' and 'S'. Magnetic scanners The magnetic scanners use the principles of magnetism to sense the document characters that have been written using magnetic ink or coded onto a magnetic strip. The two common types of magnetic scanners are: i. M agnetic in k character recogniti on (MICR) MICR  devices are used to read characters written using magnetic ink. The document characters are


typed or printed in ink containing iron II oxide that gives them magnetic property. As the document  passes into the reader the ink is magnetised and the characters are recognized by the strength of the magnetism. The magnetised characters cause current to flow through the read head depending on the magnetised surface area occupied by individual characters. The different characters are discriminated depending on the magnetic pattern that induces the different amount of currents. The MICR recognizes those patterns and conveys them to go as computer input in ter ms of electrical signals. Uses of M I CR

An example of an MICR is the cheque reader  used in banks. Usually Bank cheques use MICR to encode the cheque number, branch number of the bank and the customer’s account number along the  bottom of the cheque. This information is printed on the cheques before they are issued to the customer. When the customer writes a cheque to pay someone, the cheque is paid into a bank and it is then sent to a clearing house. At the clearing house, the amount of money is added to the bottom of the cheque in magnetic ink using a MICR encoder. The cheque can then be sorted automatically and sent back to the bank of the original customer, where the amount is deducted from his/her account. Advantages of M I CR

- MICR is difficult to forge cheques, sine it is hard to reproduce the ink. - MICR is more ‘robust’, that is, the documents can still be read even if it's folded or dirty, writtenon, etc, -  No extra peripherals are needed apart from the touch screen/monitor itself Di sadvantages of M I CR

- MICR readers and encoders are very expensive. - The system can only accept a few different characters. -  Not suitable for inputting large amounts of data - Selecting detailed objects can be difficult with fingers ii.  Magnetic card reader  A magnetic card reader is used to read data coded on a magnetic strip on a plastic card such as the one used on an automated teller machine (ATM) and credit card reader. How scanners and other reading devices work  One of the more popular scanners is a flatbed scanner, which works similarly to a copy machine except it creates a file of the document in memory instead of a paper copy.  Many scanners include OCR software, which converts a scanned image int o a text file that can be edited. D. SPEECH INPUT [VOICE RECOGNITIO]N DEVICES Data can be entered directly into a computer using voice input devices such as microphones. Voice input is the process of entering data by speaking into a microphone that is attached to the sound card, which has an analog-digital converter, on a computer. Voice recognition is the computer’s capability of distinguishing spoken words. Speech recognition software allows the user to issue commands using natural language. Old day’s voice/speech recognition software’s were speaker dependent which required to make a profile of your voice, that means you have to train the computer to recognize your voice. Today, most voice/speech recognition programs use speaker-independent software, which has a built-in set of word patterns and does not have to be trained to recognize your voice. Some voice recognition software requires discrete s peech, meaning that you have to speak slowly and separate each word with a short pause but nowadays most voice recognition products support continuous speech, allowing you to speak in a flowing conversational tone. Uses of Speech I npu t

- Electronic funds transfer. - House/car security using voice activated locks. - Office security for room access. 7

- Voice-activated toys and games. - Quality control and automation in factories. A checker whose hands are busy does not stop work to make entries in log books but instead he/she simply speaks out th e data on the products being examined. In Japan, speech input is used to control robots. - Automated materials handling - In airports, handlers speak the c ommands to direct luggage on conveyor  belts. - Computer-aided design (CAD) - A designer, e.g. architect, working at a terminal can call up design  patterns which are frequently used, instead of having to punch the catalogue numbers into a keyboard. - For people with special needs or disabilities (e.g. the handicapped especially those with impaired hands. - Emergency situations - Where faster data input is required - In language translator or programs - Voice tags for voice dialing - In automated materials handling e.g. in airports, a good handlers give spoken commands that direct the luggage to the appropriate conveyor belt. - For house/ office or car security where voice activated locks are used for access control - In voice- activated toys and games - In electronic funds transfer Advantage of speech input - Does not require training - Speech is preferred as an input because it does not require t raining - It is much faster than any other input. - information can be input while the person in engaged in other activities - Information can be fed via telephone or microphone which is relatively cheaper compared to current input systems. - Its suitable for people with special needs especially those with impaired hands - To allowing physically disabled people more work opportunities. There are extremely intelligent and skilled individuals whose limitations using computers can make them less attractive to employers. The application of speech technology instead of physical operation can allow more of these individuals to become valuable contributions to the labor force. - Speech recognition can also result in a higher level of efficiency. It can make computer users more efficient by reducing human error and improving their ability to multi-task. - Can be used in emergency situations - Businesses with customer service hotlines benefit from this type of technology because it allows them to engage their clients without a live representative, which can improve the experience for callers. In some cases, this technology can completely eliminate the need for callers to interact with a live representative. This reduces  businesses' labor costs by often allowing them to reduce the size of the staff on duty. - It can allow companies to collect information without human intervention. Many businesses employ it as a tool on their customer service hotlines. Instead of having callers remain idly on hold while agents are busy, speech recognition software allows them to input information such as the reason for their call and their account number, which can help to expedite their experiences and reduce the amount of time a representative needs to spend with each caller. Disadvantage of speech input - The phonemes in reference are recorded in isolation and it's spectrum is different from the phonemes in the input speech because they are affected by neighboring phonemes. - The same hindrance occurs when words are stored in reference template in continuous speech recognition. As already mentioned, in speaker-independent systems only isolated word recognition is commercially available. - Most buyers would like the system to be speaker independent, and uttering words in isolation can be quiet irritating especially when the input is bulk and the processing speed may not be very fast.

- Even the best speech recognition systems sometimes make errors. If there is noise or some other sound in the room (e.g. the television or a kettle boiling), the number of errors will increase. - Speech Recognition works best if the microphone is close to the user (e. g. in a phone, or if the user is wearing a microphone). More distant microphones (e.g. on a table or wall) will tend to increase the number of errors. - User may speak different languages - Local accents may not be recognized - Cannot differentiate words that have same sounds (homophones). E.g. two, to, too 8

- Accuracy rate in people with thick accents is low. -  Needs high memory, a microphone, and good program to operate successfully which may add up cost. - It cannot be used in a area where it is necessary to be quiet, such as in a library. - If you lost your voice it is hard - Word separation - connected speech has to be segmented. At present input is ‘clipped’ with distinct  pauses between words. - The response rates of speech input devices are relatively slow - Speaker variability - the speed, pitch, range, rh ythm, intonation, loudness and pronunciation of an individual speaker can ‘vary. - Can only recognise a limited vocabulary of words - most s ystems are still limited to words in isolation; connected speech is much harder to get right. - Voice input does not take care speech related problems such as accents, tone etc Input devices for physically challenged users Whether at work or at home, it may be necessary to obtain input devices that address physical limitations. Voice recognition is ideal for blind or visually impaired users, but several other input devices also are available.  A key guard, which is placed over the keyboard, allows people with limited hand mobility to rest their hands on the keyboard and guides a finger or pointing device so that only one key is pressed.  Keyboards with larger keys and on-screen keyboards on which keys are pressed using a pointing device also can help.  Pointing devices such as small trackballs controlled with a thumb or one finger and head-mounted  pointers also are available for users with motor disabilities.  Two new developments are gesture recognition and computerized implant devices. With gesture recognition the computer will be able to detect human motions. Computerized devices implanted in the  brain will allow paralyzed individuals to transmit signals to the computer.

E. OTHER DIGITAL INPUT DEVICES 1. Digitizers A digitizer, also known as graphic tablet, is made up of a flat surface and allows the user to draw an image using a stylus. The image drawn does not appear on the tablet but on the computer screen. The digitizer is used for tracing highly detailed enginee ring and architectural drawings and designs. 2. Digital cameras Digital cameras capture pictures the same way as other cameras do but the images are stored in digital form. Pictures are stored on a memory card instead of a film. The digital image taken can be streamed directly into a computer, uploaded to internet using a webcam or directl y printed using a special photo  printer. Many digital cameras allow you to review and edit the i mages while they are in the camera. You also can download, or transfer a copy of, the stored image to a computer. Once on a computer, the pictures can be edited with photo-editing software, printed, faxed, sent via electronic mail , included in another document, or posted to a Web site. There are three basic types of digital cameras.  A studio camera is a stationary digital camera used for professional studio work.  A field camera is a portable camera, often used by photojournalists, that has many lenses and other attachments.  A point-and-shoot camera  is more affordable and lightweight and provides acceptable qualit y  photographic images for the home or small business user.  Video digital cameras - used to capture pictures as well as videos. Describe the uses of PC video cameras and Web cams A PC camera is a DV camera that allows home users to record, edit, capture video and still images, and make video telephone calls on the Internet. During a video telephone call, both parti es can see each other as


they talk. Although usually placed on top of the monitor and attached to a computer’s USB port, some PC cameras are portable and can be used anywhere. A Web cam is a video camera whose output displays on a Web page. Some Web sites have live Web cams that display still pictures and update the displayed images at specified time intervals. Video Digitizer These consist of special hardware and software which converts video signals frames by frame into a digital representation in computer memory which can be saved on disk if necessary. A sequence frames can have graphics, cartoons, text added, etc. Input Devices Selection Criteria Choosing the most optimum input facility is usually not as easy task because of the involved costs and the associated operational drawbacks. The following factors are to be given consideration when selecting an input faci lity for Computer system: 1. Device Cost The initial and recurrent cost to be weighed against the expected benefits and/or operational characteristics of the facility. The cost involved in acquiring the machinery, space, Environmental requirements, media, operation etc. should be considered. 2. Device input Speed This is a crucial factor because if quicker response is required then a fast method of data collection/input e.g. the document reader may be suitable, though expensive. Note that the response required is directly proportional to the cost of the facility. 3. Data Volume The facility selected should cope with the data volume to be input with appropriate timing. 4. Device Accuracy The data being input should be accurate and give confidence and appropriateness in the inte nded application. 5. Device Reliability It is important that the facility selected is known to have a success record in the market on the application, it is to be acquired for. 6. Mode of Operation The choice of input medium depends much on the nature of the system (data processing system). For example, key-to-disk systems are more appropriate in providing fast-bulk input medium (data collect ion method! media) in an on-line system. 7. Appropriateness The most appropriate input (data collection) facilit y is arrived at by weighing out the merits and demerits of the concerned facility in the light of where it is to be applied (used). For example, the document reader may be considered to be very fast input devices suitable for (MICR  —  banking, OCR  —  billing) applications but they require standardised documents appropriate for the reader. 8. The needs of the user 9. Type of data to be input 10. Availability of the data entry device 11. Availability of space


View more...


Copyright ©2017 KUPDF Inc.