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 a

s taxes)

ergonomic keyboards

Mice and the like

As user moves mousea 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

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

Touch Screens

Sensors in or near the computer’s screenthat can detect the touch of a fingereasy to usenot suitable for complicated input

Bar Code Readers

a laser beam scans patterns of printed bars and converts them into numerical digits

faster and more accurate than manual input

Pens

use an electric pen to point and writeon a special pad or the screenused in personal digital assistantsChinese hard writing inputnot good for large amounts of text

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)

Voice Input

speech recognitionconverts sound waves into electrical waveform

into binary codespeaker dependentdiscrete word systems - user must pause

between wordscontinuous word systems are much more

difficult

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)

notebooks typically use liquid crystal displays (LCD)

a liquid crystal that is normally transparent, but turns opaque when charged with electricity

require less powerlower contrast (does not emit light)can be improved with back-lighting

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

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) 640x480Super VGA (SVGA) 800x600Extended Graphics Array (XGA) 1024x768

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

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

Plotter

a robotic arm draws with colored pensfor large drawings or images

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

Other Outputs

MicrofilmMusicComputer GraphicsVirtual Reality

Secondary Storage

Separate from the computersemi-permanentnecessary because memory is not permanent

and limited in size

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

Hard Disk

A metal coated with magnetic oxideseveral disks can be assembled into a disk packa 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

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

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-capacityread-only - recorded by the manufacturerwrite once, read-many (WORM)

CD-ROM

Compact disk, read only memoryformat 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

Floppy-Disk

floppy disks spin at ~300 RPMportableeasy back upconvenient software distributionholds 1.4 MB

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 readerTo 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

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

Magnetic Tapes

Looks like audio tapesdata is stored linearly, and measured in terms

of density:characters per inch or bytes per inchdigital audio tape (DAT) uses helical scan

recordingusually used as back up

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 tapePC users may back up onto diskettesnow Zip disks offer an alternative

100MB capacity

DVD

DVD stands for digital video diskA DVD-ROM can store from 4.7 GB(more

than seven times that of a CD-ROM) to 17 GBSuch storage capacity is needed for files

containing both text, audio, graphics, and video- in other words, multimedia.

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