Input and Output Devices

Input and Output Devices

Input and Output Devices

          Input devices

         Input devices gather data and convert them into electronic form for use by the computer.


          The principal method of data entry for entering text and numerical data into a computer

         Pointing Devices

          A computer mouse is handheld device with point-and-click capabilities that is usually connected to the computer by a cable.
          Touch screens allows users to enter limited amounts of data by touching the surface of a sensitized video display monitor with finger or a pointer.

          Source Data Automation

         Captures data in computer-readable form at the time and place they are created.

         Optical Character Recognition (OCR) devices translate specially designed mark, characters, and codes into digital form.

         Magnetic ink character recognition (MICR) technology is used primarily in check processing for the banking industry, which the bottom of typical check contains characters identifying the bank, checking account, and check number that are preprinted using a special magnetic ink.

         A MICR reader translates these characters into digital form for the computer.

         Handwriting-recognition devices such as pen-based tablets, notebooks, and notepad are promising new input technologies.

         These pen-based input devices convert the motion made by an electronic stylus pressing on a touch-sensitive tablet screen into digital form.

         Digital scanners translate image such as pictures or documents into digital form.

         Voice input devices convert spoken words into digital form for processing by the computer.

         Sensors are devices collect data directly from the environment for input into a computer system.

What Is Input?

Ø  Data or instructions entered into memory of computer
Ø  Input device is any hardware component that allows users to enter data and instructions

          What are the two types of input?

          Unprocessed text,
numbers, images,
audio, and video
          User responses

The Keyboard

          How is the keyboard divided?
          Typing area
          Numeric keypad
          Function keys, special keys that issue commands

Pointing Devices

          What is a mouse?
          Pointing device that fits under palm of hand
          Pointing device controls movement of pointer, also called mouse pointer
          Mechanical mouse has rubber or metal ball on underside

Other Pointing Devices

          What is a trackball?
          Stationary pointing device with a ball on its top or side
          To move pointer, rotate ball with thumb, fingers, or palm of hand

          What are a touchpad and a pointing stick?
          Touchpad is small, flat, rectangular pointing device sensitive to pressure and motion
          Pointing stick is pointing device shaped like pencil eraser positioned between keys on keyboard

          What are a joystick and a wheel?
          Joystick is vertical lever mounted on a base
          Wheel is steering-wheel-type input device
          Pedal simulates car brakes and accelerator

           What is a light pen?

          Handheld input device that can detect light
          Press light pen against screen surface and then press button on pen

          What is a touch screen?

          Often used with kiosks
          Touch areas of screen with finger

Keyboard and Pointing Devices

          What is a stylus and a digital pen?
          Looks like a ballpoint pen, but uses pressure to write text and draw lines
          Used with graphics tablets, flat electronic boards

Voice Input

          How does voice recognition work?
          Step 1.  A user dictates text into a microphone.

          Step 2.  An analog-to-digital converter (ADC) translates sound waves into digital measurements computer can process. Measurements include pitch, volume, silences, and phonemes. Phonemes are sound units such as aw and guh.

          Step 3.  Software compares spoken measurements with those in its database to find a match or list of possible matches.

          Step 4.  To narrow a list down, software presents user with a list of choices or uses a natural language component to predict most likely match. User may correct any selection made by software.

          What is a MIDI
(musical instrument digital interface)?
          External device, such as electronic piano keyboard, to input music and sound effects

Digital Cameras

          How does a digital camera work?

         •          Step 1.  Point to the image to photograph and take picture. Light passes into the lens of the camera.

         •          Step 2.  Image is focused on a chip called a charge-coupled device (CCD).

         •          Step 3. CCD generates an analog signal that represents the image.

         •          Step 4. Analog signal is converted to digital signal by analog-to-digital converter (ADC).

         •          Step 5.  Digital signal processor (DSP) adjusts quality of image and usually stores digital image on miniature mobile storage media in the camera.

         •          Step 6.  Images are transferred to a computer’s hard disk by plugging one end of the cable into a camera and the other end into a computer; or images are copied to hard disk from storage media used in the camera.

         •          Step 7.  Using software supplied with the camera, images are viewed on screen, incorporated into documents, edited, and printed.

          What is resolution?

Ø  Sharpness and clarity of image
Ø  The higher the resolution, the better the image quality, but the more expensive the camera
Ø  Pixel (picture element) is single point in electronic image
§  Greater the number of pixels, the better the image quality

Video Input

          What is video input?

          Process of entering full-motion images into computer
          Video capture card is adapter card that converts analog video signal into digital signal that computer can use
          Digital video (DV) camera records video as digital signals

          What are a PC video camera and a Web cam?

          PC video camerac—cDV camera used to capture video and still images, and to make
video telephone calls on Internet
          Also called PC camera
          Web camc—cvideo camera whose output displays on a Web page

Scanners and Reading Devices

          What is a scanner?

          Light-sensing device that reads printed text and graphics
          Used for image processing, converting paper documents into electronic images

          How does a flatbed scanner work?

          Step 1.  Document to be scanned is placed face down on the glass window.

          Step 2.  Bright light moves underneath scanned document.

          Step 3.  Image of the document is reflected into a series of mirrors.

          Step 4.  Light is converted to analog electrical current that is converted to digital signal by an analog-to-digital converter (ADC).

          Step 5.  Digital information is sent to memory in the computer to be used by illustration, desktop publishing, or other software; or it is stored on disk.

            •          Step 6.  Users can print image, e-mail it, include it in a document, or place it on a                     Web page.

          What is an optical reader?

Ø  Device that uses light source to read characters, marks, and codes and then converts them into digital data
Ø  Optical character recognition (OCR) reads characters in
OCR font

Ø  Optical mark recognition (OMR) reads hand-drawn pencil marks, such as small circles

Ø  What is a bar code reader?

Ø  Uses laser beams to read bar codes

Ø  What is a magnetic-ink character recognition (MICR) reader?

Ø  Can read text printed with magnetized ink
Ø  Banking industry almost exclusively uses MICR for check processing

Ø  What is biometrics?

Ø  Authenticates person’s identity by verifying personal characteristic

Ø  Fingerprint scanner captures curves and indentations of fingerprint
Ø  Hand geometry system measures shape and size of person’s hand

Biometric Input

          What are examples of biometric technology?

          Voice verification system compares live speech with stored voice pattern

          Signature verification system recognizes shape of signature

          Iris recognition system reads patterns in blood vessels in back of eye
          Biometric data is sometimes stored on smart card, which stores personal data on microprocessor embedded in card

        Output Devices


         Display data after they have been processed.

         Cathode Ray Tube (CRT)

          The most popular form of information output.
          It works much like a television picture tube, with an electronic gun shooting a beam of electrons to illuminate the pixels on the screen.


          Produce a printed hard copy of information output.
          Include impact printers ( dot-matrix printer), and non-impact printers (laser, inkjet, and thermal transfer printers).


          To created high-quality graphics documents with multicolored pens to draw computer output.
          Slower than printers but are useful for outputting large-size charts, maps or drawing.

         Voice output devices
          Converts digital output data into intelligible speech.

          To deliver an audio output such as music, that is connected to the computer.

          What is output?

         Data that has been processed into a useful form,
          Output device is any hardware component that can convey
information to user

          What is a display device?

         Output device that visually conveys information
          Information on display device sometimes called soft copy

         Monitor houses display device as separate peripheral

CRT Monitors

          What is a CRT monitor?
          Contains cathode-ray tube (CRT)

          Screen coated with tiny dots of phosphor material
          Each dot consists of a red, blue, and green phosphor

          Common sizes are 15, 17, 19, 21, and 22 inches
          Viewable size is diagonal measurement of actual viewing area

          How does video travel from the processor to a CRT monitor?
          Video card (also called a graphics card) converts digital output from computer into analog video signal

          Step 1. The processor sends digital video data to the video card.

          Step 2. The video card’s digital-to-analog converter (DAC) converts the digital video data to an analog signal.

          Step 3. The analog signal is sent through a cable to the CRT monitor.

          Step 4. The CRT monitor separates the analog signal into red, green, and blue signals.

          Step 5. Electron guns fire the three color signals to the front of the CRT.

          Step 6. An image is displayed on the screen when the electrons hit phosphor dots on the back of the screen.


          What is a printer?
          Output device that produces text and graphics on paper
          Result is hard copy, or printout
          Two orientations: portrait and landscape

Speakers and Headsets

          What is an audio output device?

          Computer component that produces music, speech, or other sounds
          Speakers and headsets are common devices

          What is voice output?

          Computer talks to you through speakers on computer
          Internet telephony allows you to have conversation over Web

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