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Input Devices - Keyboard

Input Devices - Keyboard. Similar to a typewriter keyboard alphanumeric keys tab, shift, capslock, enter numeric keypad function keys special keys: escape, control, alternate can be designed for various languages Chinese keyboard (which input method?) on applications

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Input Devices - Keyboard

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  1. Input Devices - Keyboard • Similar to a typewriter keyboard • alphanumeric keys • tab, shift, capslock, enter • numeric keypad • function keys • special keys: escape, control, alternate • can be designed for various languages • Chinese keyboard (which input method?) • on applications • fast food (keys correspond not to characters but products, or functions such as taxes) • ergonomic keyboards

  2. Mice and the like • As user moves mouse • a ball under the mouse rolls on a flat surface, the movements of the ball are translated into movements of the cursor • connected to the computer’s bus • through a mouse socket to a circuit board (“card”) • through a serial port (a socket) to which user can connect external devices such as mouse or modem • point, click, double-click, drag

  3. Track Ball • An upside-down mouse • user rolls the ball directly • requires less space • Optical Mouse • a photo-detector senses the mouse’s movement over a special pad with gridlines printed on it

  4. Touch Screens • Sensors in or near the computer’s screen • that can detect the touch of a finger • easy to use • not suitable for complicated input

  5. Bar Code Readers • a laser beam scans patterns of printed bars and converts them into numerical digits • faster and more accurate than manual input

  6. Pens • use an electric pen to point and write • on a special pad or the screen • used in personal digital assistants • Chinese hard writing input • not good for large amounts of text

  7. Scanners • converts image into a digitized form - a bit map • shines light onto an image and measures intensity of the reflection at every point • optical character recognition (off-line recognition is harder)

  8. Voice Input • speech recognition • converts sound waves into electrical waveform into binary code • speaker dependent • discrete word systems - user must pause between words • continuous word systems are much more difficult

  9. Output devices - The Monitor • the typical monitor users a cathode ray tube (CRT) • an electron gun systematically aims at every phosphor dot on the screen to reproduce an image - a pixel grows • the brightest and clearest for the money • a monochrome tube has only one beam • a color monitor has 3 beams (red, green, blue) • horizontal and vertical resolutions (e.g., 800x600, 1024x768, 1280x1024) • flicker appears when a monitor scans too slowly • refresh rate = the number of times the monitor repaints the entire screen each second (e.g., 60 Hz , 75 Hz)

  10. notebooks typically use liquid crystal displays (LCD) • a liquid crystal that is normally transparent, but turns opaque when charged with electricity • require less power • lower contrast (does not emit light) • can be improved with back-lighting

  11. The Video Controller • goes between the monitor and the CPU • contains the memory an other circuitry necessary to send information from the CPU to the monitor • dual port memory allows data to be stored into the memory from the CPU while the controller sends the data to the monitor • text mode • 80 columns x 25 rows of cahracters • 2 bytes per character position • controller reads the byte that specifies the character and displays the dot pattern • fast • cannot display complex graphics

  12. graphics mode • all points addressable • amount of memory required per pixel depends on number of color that can be displayed by the monitor • generations of graphics modes • Color Graphics Adaptor (CGA) • Enhanced Graphics Adaptor (EGA) • Video Graphics Adaptor (VGA) 640x480 • Super VGA (SVGA) 800x600 • Extended Graphics Array (XGA) 1024x768

  13. Printers Dot Matrix • first printers used with PCs • pins on a print head strike the paper through an inked ribbon to create an image • from 9 pins to 24 pins • have text modes and graphics modes • low image quality, slower, and noisier • cheaper • suitable for multi-copy forms

  14. Ink Jet • spray ink directly on paper through up to 64 nozzles • quiet, not very fast Laser • laser writes on a +ve charged drum • charge neutralized where laser writes • toner sticks to neutral spots • toner transferred to paper from drum

  15. Plotter • a robotic arm draws with colored pens • for large drawings or images

  16. Voice Output • speech synthesis is easier than speech recognition • voice synthesizers convert data into vocalized sounds • synthesis by analysis - • analyze the human voice input • store the spoken sounds • reproduce the sound when needed • more natural, but limited to the number of words stored • synthesis by rule • apply linguistic rules to create artificial speech

  17. Other Outputs • Microfilm • Music • Computer Graphics • Virtual Reality

  18. Secondary Storage • Separate from the computer • semi-permanent • necessary because memory is not permanent and limited in size

  19. Magnetic Disk • Diskettes, hard disks, and tape are magnetic • The surfaces are coated with iron particles • Each bit is stored on a magnetized spot on the disk: magnetized: 1; otherwise: 0 • The surface of each disk has concentric tracks of spots • to write:electromagnets on read/write heads magnetize/demagnetize the iron particles • to read: the presence/absence of magnetism in the spot is detected by the read/write head • the disk drive is a device that reads/writes to the disk

  20. Hard Disk • A metal coated with magnetic oxide • several disks can be assembled into a disk pack • a disk drive is a machine that can read/write on a disk, a disk pack is mounted on a disk drive, separate from the computer • all disks in a disk pack rotate together, although only one disk is being read/write at one time

  21. If the head touches the surface, it is a head crash and data may be destroyed • a disk pack has a stack of access arms which slips between the disks • most disk packs combine the disks, arms, and heads in a sealed module called a Winchester disk

  22. Optical disks • The surface of the disk is coated with a metallic material • a laser makes tiny spots on the surfaces, altering the way light is reflected • cheap, compact, high-capacity • read-only - recorded by the manufacturer • write once, read-many (WORM)

  23. CD-ROM • Compact disk, read only memory • format identical to audio CDs - plants making audio CDs can easily produce CR-ROMs to distribute software • up to 660 megabytes ~= 400 3-1/2 inch diskettes • there are now also record able CD-ROMs

  24. Floppy-Disk • floppy disks spin at ~300 RPM • portable • easy back up • convenient software distribution • holds 1.4 MB

  25. CD-R(ecordable) • A record able CD-ROM technology using a disc that can be written only once • the discs can be read on any CD-ROM reader • To record a full 650MB disc takes from 20 minutes to an hour depending on the speed of the drive • large numbers of CD-ROMs are duplicated on a pressing machine from a master plate derived from the original CD-R recording

  26. Drive Performance • Average access time (to position the head) floppy disk ~200 milliseconds hard disk ~15 milliseconds CD-ROM ~100 milliseconds • data transfer rate • MB per second

  27. Magnetic Tapes • Looks like audio tapes • data is stored linearly, and measured in terms of density:characters per inch or bytes per inch • digital audio tape (DAT) uses helical scan recording • usually used as back up

  28. Back up • Data in a computer may be corrupted by head crashes in the hard disk, other hardware errors, software errors, and human errors. • Hence it is prudent to store data in more than one place to protect it from damage or errors • large organizations usually back up on magnetic tape • PC users may back up onto diskettes • now Zip disks offer an alternative • 100MB capacity

  29. DVD • DVD stands for digital video disk • A DVD-ROM can store from 4.7 GB(more than seven times that of a CD-ROM) to 17 GB • Such storage capacity is needed for files containing both text, audio, graphics, and video- in other words, multimedia.

  30. Small Computer System Interface (SCSI) • Originally designed to connect 3rd party peripheral devices to IBM mainframes • popular, used on all sorts of computers • all circuitry on the drive itself • connects the drive to the system bus itself • high transfer rates • can be considered an extension of the system bus • several devices can be connected in a chain to a single SCSI port

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