2. input output storage

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Input & Output DevicesInput & Output Devices

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Input DevicesInput Devices
 Input devices are used to feed data and
instructions to the computer systems.
 They consist of a range of devices that take
data and programs from the outside world that
people can read or comprehend and convert
them to a form that the computer can
manipulate.

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Input DevicesInput Devices
 The form of the input devices :
 Keyboard, Pointing device
 Writing & drawing input devices
 Video, Text, voice input

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Key board
 It’s similar as normal typewriter
keyboard, plus a number of special keys.
 Standard keys are used to enter words &
numbers. Special keys so called “function
keys” labeled as F1,F2 ... are used to
enter commands.
 A numeric keypad that resembles an
electronic calculator’s keypad.

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Key board
 Cursor-movement key
 104-key enhanced keyboard
 Used for data entry and to issue commands
into the system.

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Traditional KeyboardTraditional Keyboard

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Pointing device - Mouse
 A mouse is a device that can be rolled on a
desktop to direct a pointer (cursor) on the
computers display screen. The cursor is the
symbol on the screen that shows where data
may be entered next or the command to be
activated.
 Pointing devices commonly have two or three
buttons that are used to issue commands to the
computer.

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Pointing device - Mouse
 Command Actions
 Point - an act of moving the pointing
device to an object on-screen.
 Click - select the object on-screen.
 Drag - holding down the pointing-device
button while moving the selected object on-
screen.

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Pointing device - Trackball
 A trackball performs like a stationary, upside-
down mouse.
 Most portable laptop computers use a built-in
or clip-on trackball.

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Pointing device - Joystick
 A joystick is a small lever that
can be moved in any direction
to move an object on the screen.
 Usually associated with playing
computer games.

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Graphics Input - Scanner
 Image scanners or graphic
scanners convert the printed or
photographic image on paper into
electronic signals and then into
digital form.
 These digital information then can
be stored in a computer &
manipulated.

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Text Input - Scanner
 Text are scanned from the printed page
into the computer, as an attempt to reduce
errors in data entry while speeding up the
process as well.
 The software incorporated converts the
scanned images into character codes and
thus enables text processing.

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Text Input - OCR
 Optical Character Recognition (OCR)
 An input device that can read and recognise
the symbols of text (special printed characters)
& convert them to the machine readable form.

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Writing & Drawing Input
Devices - Light Pen
 The light pen is a light sensitive stylus, or pen
like device, connected by a wire to the
computer terminal.
 The user brings the pen to a desired point on
the display screen and presses the pen button,
which identifies that screen location to the
computer.

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Devices - Touch Screen
 The touch screen is
video display screen
that has been sensitized
to receive input from the
touch of a finger.

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Devices - Digitizing Tablet
 A digitizing tablet consists of a tablet
connected by a wire to a stylus or puck.
 A stylus is a pen like device with which the
user “sketches” an image.
 A puck is a copying device with which the
user copies an image as it is moved over a
desired path on a sketch.

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Devices - Digitizing Tablet
 More sophisticated
stylus or pointing
devices with high
accuracy are used by
designers, architects,
artists, desktop
publishers, map makers,
etc.

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Video input
(Digital Camera)
 As with sound, most films & video are
generated and recorded in analog forms in
which the signals are in continuously varying
nature. Thus the signals come from the systems
such as VCR, videodisk or laser disk, or a
camcorder must be converted to digital form
through a special video capture card installed
in the computer.

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Video input
 Two type of video cards:
 Frame grabber video card
• Can capture & digitize only a single frame at a
time.
 Full motion video card
• Can convert analog to digital signals at the rate
of 30 frames per second, giving the effect of a
continuously following motion picture.

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Voice input
(Voice Recognition)
 Converts the person’s
speech in to digital code
by comparing the
electrical patterns
produce by the
speaker’s voice with a
set of prerecorded
patterns stored in the
computer.

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Source Data Input - MICR
 Magnetic Ink Character Recognition (MICR)
 MICR characters which are printed with magnetic
ink , containing magnetic particles are read by
MICR equipment producing digitised signals.
 Used by banks to read the information such as
printed serial numbers on the bottom of cheques
using magnetic ink.
 MICR reader/sorter can process cheques and other
documents at speeds of up to 2000 documents per
minute.

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Source Data Input – Magnetic strip
 Used on the backs of credit cards and bank
debit cards, and various other plastic cards.
 Enables readers, such as automated teller
machines (ATM) to read account information.

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Source Data Input - OMR
 Optical-Mark Recognition (OMR)
 An input device that senses marks on a piece
of paper, using a light beam, and converts
them into electronic signals which are sent to
the computer for processing.
 Commonly used to mark the questionnaires or
school examination answer sheets where the
students, using pencils mark certain boxes on
the examination answer sheets provided.

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Source Data Input - Bar codes
 Commonly used by
sales and stock people
in retail stores and
supermarkets.
 Point-of-sale (POS)
terminal scans the bar
codes of the Universal
Product Code (UPC) to
register the price, which
is programmed into the
host computer, as well
as to deduct the item
from stock.

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Output devicesOutput devices
 Translate information processed by the
computer into a form that human or another
machine can recognize.
 The two principle kind of outputs are
hardcopy & softcopy .
 Hardcopy refers to a printed output.
 Softcopy refers to the information that is
shown on the display screen or is in
audio or video form.

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 There are several ways
to produce output:
 Text output
 Graphics output
 Sound output
 Video output

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 Text Output :
 Simply the alphanumeric characters that
make up our language. Text output
appearance ranges from typewritten to
typeset quality.

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 Graphics Output :
 Includes line drawings, maps, presentations
business graphics, computer-aided design,
computer painting, photographic
reproduction.

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 Sound output :
 Ranges from the message beeps produced
by the computer system to the human voice
to music and other forms of sound.

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 Video output :
 Photographs (still images) or moving
images such as television and videotaped
material.

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PrintersPrinters
 A printer provides hard copy output on paper.
The basic criteria for evaluating printers
include:
 QualityQuality of the printed output.
 SpeedSpeed at which printed pages are produced.
 SoundSound levellevel during printing.
 CostCost of printing media (ribbons, cartridges).
 ConservationConservation of paper.

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 Translates information that has been processed byTranslates information that has been processed by
the system unitthe system unit
 OutputOutput referred to as hard copyreferred to as hard copy
 FeaturesFeatures
• ResolutionResolution
• Color capabilityColor capability
• SpeedSpeed
• MemoryMemory

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PrintersPrinters
 Impact Printers :
 Form characters or images by striking a
mechanism such as print hammer or wheel against
an inked ribbon leaving an image on paper. Make
high noise. Now used less.
 Non- Impact Printers :
 Form characters or images without making direct
physical contact between printing mechanism and
paper.

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Impact PrintersImpact Printers
 First printing technology.
E.g. 24 Pin Okidata Dot Matrix Printers - 475 cps
 Early days typewriters were adapted, produced same
high-quality output.
 Cannot change fonts nor can print graphics or
colours. Only the symbols available in the printing
mechanism can be produced on the paper.
e.g. daisy wheel printer, drum and belt printers.

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Impact PrintersImpact Printers
 Followed by dot-matrix printers.
 Dot-matrix output is produced by printers that
use wires in the print head. These wires extend
out in different patterns, pressing against the
ribbon to print the characters on paper. As this
mechanism enables the print control up to the
dot level on the paper, the can be used to
produce both text and graphics.
 Fast, but noisy. Wear out ribbons very quickly.

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Non-Impact Printers –Non-Impact Printers –
Laser PrintingLaser Printing
 Provide high-quality non-impact printing. Output is
created by directing a laser beam onto a drum to
create an electrical charge that forms a pattern of
letters or images.
 As the drum rotates, it picks up black toner on the
images and transfers them to paper. The heating
process then fixes the toner particles permanently
on the paper.

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Laser PrintingLaser Printing
 Excellent print quality and font selection.
 Fast printing.
E.g. 8-500 pages per minute
 High quality graphics with colour. High resolution.
 Medium level noise, but high cost.
 Primary disadvantages are expensive maintenance
and the high cost of toner cartridges.

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Inkjet PrintingInkjet Printing
 Inkjet printer transfers characters and images
to paper by spraying a fine jet of ink.
 Offers nearly the quality of laser printing, but
not the speed. Low-cost alternative for high
quality printing.

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PlottersPlotters
 It is a specialized output device designed to produce
high-quality graphics in a variety of colours. That are
especially useful for creating maps and architectural
drawings, although they may also produce less
complicated charts and graphics.
 Type of plotters :
 Pen plotter
 Electrostatic plotter
 Thermal plotter

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MonitorsMonitors
 Known as screens orKnown as screens or
display screensdisplay screens
 Output referred to asOutput referred to as
soft copysoft copy
 FeaturesFeatures
• Resolution-pixelsResolution-pixels
• Dot pitchDot pitch
• Refresh rateRefresh rate
• SizeSize

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 Cathode-ray tubeCathode-ray tube oror
CRTsCRTs
 Flat-panelFlat-panel
• Require less power toRequire less power to
operateoperate
• Portable and thinner thanPortable and thinner than
CRTsCRTs
 Other monitorsOther monitors
• E-booksE-books
• Data projectorsData projectors
• High-definition televisionHigh-definition television
(HDTV)(HDTV)

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Video MonitorVideo Monitor
 Provides soft copy output.
 Comes in either monochrome
or colour.
 A monochrome display a single colour
against a different coloured background,
such as green on black amber on black
or white on black.
 Colour display can show a variety of
colours.

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Video DisplaysVideo Displays
 Resolution - describes the degree of
details in a video display.
 The higher the resolution the characters
and images are sharper and crisper as
film image.
 Conventional television display is low
resolution as we can see lines, jagged
edges and graininess in the image.

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 Bit-mapped display offers extremely
high-resolution. Bit map means that each
dot on the screen, called a pixel (for
picture element) is represented by one bit
(a 1 or 0) by the computer. (monochrome)
 Bit-mapped graphics is the colour version
of a bit map display. Each pixel identifies
a number (e.g. 1-256 on a 256-colour
palette) indicating what colour that pixel
should be.

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 The liquid crystal display (LCD) is a
flat-screen display commonly used with
portable computers.

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TerminalTerminal
 A monitor-keyboard combination.
 Has no system unit of its own, but instead uses
the facility from a central computer via a
communication link.
 Mainframes, minicomputers and workstation
systems support multiple terminals.

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TerminalTerminal
 Dumb terminal performs the simplest input
and output operations but no processing.
e.g. A bank ATM
 Smart (intelligent) terminal may have its
own CPU or processing capabilities, as well as
built-in disk for storage.
e.g. Point-of-sale (POS) cash register

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Optical Storage DevicesOptical Storage Devices
 Data recording is done by using laser technology.Data recording is done by using laser technology.
 Types of Optical Storage Devices :Types of Optical Storage Devices :
 Compact Disk Read Only Memory (CD-ROM)Compact Disk Read Only Memory (CD-ROM)
 Compact Disk Recordable drives (CD-R)Compact Disk Recordable drives (CD-R)
 CD-ROM PlayersCD-ROM Players
 CD-ROM TowersCD-ROM Towers
 Erasable Optical Disk (EOD)Erasable Optical Disk (EOD)
 CD-ROM JukeboxesCD-ROM Jukeboxes
 DVD-ROM DrivesDVD-ROM Drives
 Magneto-optical DrivesMagneto-optical Drives
 Optical storage mediaOptical storage media

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CD-ROMCD-ROM
 Holds approximately 650 MBHolds approximately 650 MB
 Used for :Used for :
 Data StorageData Storage
 EncyclopaediasEncyclopaedias
 CataloguesCatalogues
 GamesGames
 EntertainmentEntertainment
 MoviesMovies
 Magazines and booksMagazines and books

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DVD DevicesDVD Devices
 OriginallyOriginally- Digital Video Disk (DVD)- Digital Video Disk (DVD)
 NowNow - Digital Versatile Disk (DVD)- Digital Versatile Disk (DVD)
 Refers to a storage medium that can store TV-qualityRefers to a storage medium that can store TV-quality
images on a CD-ROM disk with a capacity exceedingimages on a CD-ROM disk with a capacity exceeding
5 GB.5 GB.

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Removable media drivesRemovable media drives
 Including tape drives, zip, LS120, and DAT drivesIncluding tape drives, zip, LS120, and DAT drives
except floppy drives.except floppy drives.
 Magnetic TapesMagnetic Tapes
 Very popular with mainframe computers.Very popular with mainframe computers.
 Storage density is expressed in ‘bytes per inch’Storage density is expressed in ‘bytes per inch’
((bpibpi) or character per inch () or character per inch (cpicpi).).
 Storage density varies with the quality of theStorage density varies with the quality of the
tape & the equipment used to read form andtape & the equipment used to read form and
write on it.write on it.

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Magnetic TapesMagnetic Tapes
 Tape width = ½ inchTape width = ½ inch
 Data storage in tracksData storage in tracks
 Tape tracks = 9Tape tracks = 9
 Data recorded in blocks of charactersData recorded in blocks of characters
 Read/write speed = 50 ips (inches per second)Read/write speed = 50 ips (inches per second)
 Recording density = 1,600 bpi (bytes per inch)Recording density = 1,600 bpi (bytes per inch)
 Tape length = 2400 feet = 28,800 inchesTape length = 2400 feet = 28,800 inches

Storage capacityStorage capacity 40 MB40 MB

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Magnetic TapesMagnetic Tapes
 Time to write a block = 128 msTime to write a block = 128 ms
 Tape start/stop time = 0.02 sec = 20 msTape start/stop time = 0.02 sec = 20 ms
 Time to write a block + start and stop timesTime to write a block + start and stop times
= 20 + 128 + 20 = 168 ms= 20 + 128 + 20 = 168 ms

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Digital TapeDigital Tape
 Magnetic tapeMagnetic tape
 A tape made of thin plastic with a magneticallyA tape made of thin plastic with a magnetically
layer on which data can be stored.layer on which data can be stored.
 Digital tape store data in digital format, instead ofDigital tape store data in digital format, instead of
analogue format.analogue format.

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ZIP DevicesZIP Devices
 Zip drive (portable or internal) uses a special 3.5 inchZip drive (portable or internal) uses a special 3.5 inch
disk that holds 100 Mb or 250 MB.disk that holds 100 Mb or 250 MB.

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Hard Disk Drive (HDD)Hard Disk Drive (HDD)
 The mechanism that reads and writes data on a hardThe mechanism that reads and writes data on a hard
disk.disk.
 A sealed unit that a PC uses for nonvolatile dataA sealed unit that a PC uses for nonvolatile data
storage.storage.
 HDDs are sometimes calledHDDs are sometimes called Winchester drives.Winchester drives.
 Used to store crucial programming and data.Used to store crucial programming and data.
 Contains rigid, disk-shaped platters, usuallyContains rigid, disk-shaped platters, usually
constructed of aluminum or glass.constructed of aluminum or glass.
 Many disk drives improve their performance through aMany disk drives improve their performance through a
technique calledtechnique called cachingcaching..

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Hard Disk Drive OperationHard Disk Drive Operation
 HDD consists of spinning disks with headsHDD consists of spinning disks with heads
that move over the disk and store data inthat move over the disk and store data in
tracks and sectors.tracks and sectors.
 The heads read and write data in concentricThe heads read and write data in concentric
rings called tracks.rings called tracks.
 Tracks are divided into segments calledTracks are divided into segments called
sectors which store 512 bytes.sectors which store 512 bytes.
 Disk consists of several platters (e.g. 3).Disk consists of several platters (e.g. 3).
Each platter has two sides. A number refersEach platter has two sides. A number refers
to each side (e.g. side 0, 1, 2, 3 for 4to each side (e.g. side 0, 1, 2, 3 for 4
surfaces). A Disc pack may have 20 surfacessurfaces). A Disc pack may have 20 surfaces
or = 11 Plattersor = 11 Platters
 The platters can’t bend or flex.The platters can’t bend or flex.

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Magnetic Disk (Hard Disk)Magnetic Disk (Hard Disk)
 Removable Disk :Removable Disk :
 Removable disk pack used in earlier Mainframe &Removable disk pack used in earlier Mainframe &
Mini Computers.Mini Computers.
 Disk cartridge - easy to remove like cassettes.Disk cartridge - easy to remove like cassettes.
 Fixed Disk :Fixed Disk :
 Installed in a sealed container and it’s notInstalled in a sealed container and it’s not
removable.removable.
 most of the fixed disks use the “Winchester”most of the fixed disks use the “Winchester”
technology.technology.

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Magnetic DiskMagnetic Disk
 A disk starts out very unstructured – just a lot of bitsA disk starts out very unstructured – just a lot of bits
of magnetic stuff without any organisation, rhyme orof magnetic stuff without any organisation, rhyme or
reason. Before the system can start writing records toreason. Before the system can start writing records to
it, the disk must have a structure a grid work intoit, the disk must have a structure a grid work into
which the information can be placed.which the information can be placed.
 Formatting a disk is the process of putting the gridFormatting a disk is the process of putting the grid
work on the disk and building the organisationalwork on the disk and building the organisational
structure so that file can be found. Once a disk isstructure so that file can be found. Once a disk is
formatted it is ready for the system to write data to it.formatted it is ready for the system to write data to it.

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 Formatting organises disks into numbered ringsFormatting organises disks into numbered rings
called cylinders. A cylinder on a single side iscalled cylinders. A cylinder on a single side is
referred to as a track.referred to as a track.
 Each track is broken into numbered pie slices calledEach track is broken into numbered pie slices called
sectors. Each sector stores information.sectors. Each sector stores information.

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For an example,For an example,
 Disk packDisk pack = 20 surfaces = 11 Platters= 20 surfaces = 11 Platters
 Disk = 2048 cylinders (figure has only 4)Disk = 2048 cylinders (figure has only 4)
 Cylinder = 20 tracks (track in each surface)Cylinder = 20 tracks (track in each surface)
 Track = 72 sectors (figure outermost has 13)Track = 72 sectors (figure outermost has 13)
 Sector = 512 bytesSector = 512 bytes
 Disk Storage = 512 * 72 * 20 * 2048 bytes = 1.44 GBDisk Storage = 512 * 72 * 20 * 2048 bytes = 1.44 GB
 Rotational speed = 3600 rpm (revolutions per minute)Rotational speed = 3600 rpm (revolutions per minute)
= 16.66 ms per revolution= 16.66 ms per revolution

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 The time required to position the read-write heads over theThe time required to position the read-write heads over the
required track is the seek time.required track is the seek time.
 The time required for the read-write head to come to aThe time required for the read-write head to come to a
complete stop after it is moved is called the settling time.complete stop after it is moved is called the settling time.
 The time required for the disk to rotate to the position whereThe time required for the disk to rotate to the position where
the beginning of the desired block arrives at the read-writethe beginning of the desired block arrives at the read-write
head is latency.head is latency.
 Average Rotational delay (latency) = ½ revolutionAverage Rotational delay (latency) = ½ revolution
 Track capacity = 72 x 512 = 36 KBTrack capacity = 72 x 512 = 36 KB
 Cylinder capacity = 20 x 36 = 720 KBCylinder capacity = 20 x 36 = 720 KB
 Disk capacity = 2048 x 720 = 1.44 GBDisk capacity = 2048 x 720 = 1.44 GB

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Hard Disk DriveHard Disk Drive

08/16/13 67
Hard Disk Technology –Hard Disk Technology –
RAID SystemsRAID Systems
 Stands for Redundant Array of Independent (orStands for Redundant Array of Independent (or
Inexpensive) Disk.Inexpensive) Disk.
 Designed to improve the fault tolerance andDesigned to improve the fault tolerance and
performance of computer storage systems.performance of computer storage systems.
 The main purpose is to increase the reliability andThe main purpose is to increase the reliability and
availability.availability.
i.e. If one disk fails, still no data is lost.i.e. If one disk fails, still no data is lost.
 RAID is an assembly of disk drives, known as diskRAID is an assembly of disk drives, known as disk
array, that operates as one storage unit.array, that operates as one storage unit.

08/16/13 68
 RAID functions are:RAID functions are:
 Immediate availability of data and, dependingImmediate availability of data and, depending
on the RAID level, recovery of lost data.on the RAID level, recovery of lost data.
 Redundancy of data at a chosen level.Redundancy of data at a chosen level.
 Depending on the level of RAID, this method of dataDepending on the level of RAID, this method of data
storage provides the data redundancy needed for astorage provides the data redundancy needed for a
highly secure system, with additional benefit of fasterhighly secure system, with additional benefit of faster
retrieval of data through multiple channel access.retrieval of data through multiple channel access.

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 The array includes drives, controllers, enclosure,The array includes drives, controllers, enclosure,
power supplies, fans, cables, etc. and software.power supplies, fans, cables, etc. and software.

08/16/13 70
ModemsModems
 A device used to provide remote connectivity over the
Telephone lines.
 For two modems to communicate, must share the same
protocol.
 Protocol :Protocol :
 Determines how two entities will communicate.Determines how two entities will communicate.

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ModemsModems
 Connection of informationConnection of information
superhighway is by way of a modem.superhighway is by way of a modem.
 This is connected to the serial port ofThis is connected to the serial port of
the computer.the computer.
 The faster modem, the less the time itThe faster modem, the less the time it
will take to download files to thewill take to download files to the
computer. If long distance telephonecomputer. If long distance telephone
charges are involved higher speedcharges are involved higher speed
modems can save cost as well time.modems can save cost as well time.
 Modems with speeds as high as 56,000Modems with speeds as high as 56,000
baud are advisable.baud are advisable.

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ModemsModems
 It converts digital data used by the computers intoIt converts digital data used by the computers into
analog signals for transmission over the telephoneanalog signals for transmission over the telephone
line & converts the analog signals back to digitalline & converts the analog signals back to digital
data. (Modulator & Demodulator)data. (Modulator & Demodulator)
 Three modulation methods are:Three modulation methods are:
 Frequency-shift keying (FSK)Frequency-shift keying (FSK)
 Phase-shift keying (PSK)Phase-shift keying (PSK)
 Quadrature amplitude modulation (QAM)Quadrature amplitude modulation (QAM)

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