Supper floppies  -- Zip drives, LS120, HiFD

  • Rapid growth in HDD & slow growth in FDD
  • Cheap
  • Good for back up
  • Portable PC card version available

Zip drive (Bernoulli’s box) – Inventor – Iomega 

  • Similar to floppy but use zip cartridge for media
  • Twice thicker than floppy disk
  • Size: 4 inch square
  • Capacity: 100MB & 250 MB
  • Variable sectors/track – max usable disk space
  • Better reliability & portability
  • Used for OS installation without CD/Several floppy
  • Can be internal or external drive

Type of Interfacing

Ls 120

  • 120MB std aims to replace regular fdd
  • Can read 31/2” floppy faster
  • SCSI version of ZIP faster than LS120 drive

Hifd (high floppy disk – sony’s)

  • Capacity of 200MB on 31/2” floppy disk
  • Can read & write old & new floppy disk
  • Faster than LS120 drives

Mo drives (magnetic optic drives)

  • Magnetic medium
  • Laser beam-laser guided magnet heats very minute area 300o C
  • During Read, Laser beam detects polarization of micro magnets
  • Fast
  • Extremely stable
  • Wear Proof
  • Data Life Span: 30years
  • Popular: Sony’s Recordable Mini Disc

MODEM

  • MODulator Cum DEModulator
  • I/O device to link computer  to telephone line to communicate with another computer
  • Transmits voice and data as analog signals
  • Transmits digital data into analog voltages & transmit over telephone line
  • Receiving end – another modem converts analog to digital data
  • Now, a house hold device

Fax modem

  • Modem with additional capability of sending & receiving faxes
  • Fax- s/w transmits document in a system
  • Files can be printed if needed

Cd rom drive (Compact disk read only memory)

  • Read only device – large capacity – low cost
  • Essential in multimedia system
  • Highly reliable
  • Uses optical technology
  • Storage capacity: 680Mb – Larger
  • Speed: HDD > CD Drive > FDD

Storing Information

  • Laser beam used for storing information
  • Data on CD is stored on single continuous spiral track from centre of length is 5Km & 650Mb that is divided into sector 
  • Track Density – very high
  • Gap between tracks is 1.6 microns
  • Data bits – represented by “pit” (1) & “land” (0)
  • Land reflects & Pit does not reflect
  • While recording a laser burns spots on disk forming pits & lands
  • During reading, laser beam is focused on the track
  • Light reflected from Land > Pit

Cross section of a CD media

Sectors

  • CD is made of reflective material encased in plastic layer
  • Each sector stores 2048 bytes of data
  • In each sector a 12 byte sync field & 4 byte header field
  • Sector address format – mins:Secs:Sector
    • First sector – 00:00:00
    • Second sector – 00:00:01
    • 1st three sectors – reserved & no user data
    • Equal length for all sectors

CD-ROM drive operation

  • Constantly changing rotational speed
  • Linear Velocity (CLV): On reading outer area, single speed CD ROM Drive spins at 200rpm & on reading inner area – 530 rpm
  • CD-ROM drives spin faster than CD players
  • CD’s Data transfer is 150 Kb/Sec
  • CD-ROM’s speed is specified as multiple of data transfer rate of CD – 1x, 2x, 4x, 36x, 48x, etc

Advantages of CD ROM drives

  • Both readable & Writable CD available
  • Essential for multimedia application
  • Distribution medium by software suppliers
  • Not Sensitive to dust, scratch, magnetic fields & temperature variation
  • Large capacity & High reliability

CD-R Drive (Compact Disk – Recordable) (Burner)

  • It has once only writable capability
  • Uses: To distribute s/w, S/w backup, File archiving
  • A Preformed raised grove is present
  • Pits are burnt on groove by firing laser on hot layer organic dye
  • Can read from CD – R
  • Std Capacity: 628MB & 737MB

CD – RW Drive (Compact Disk – Rewritable)

  • Can read & write
  • Re-burning of 1000 times is possible 
  • Phase-change alloy forms recording layer
  • Over writing data is  done with 2 different temperature & laser beam alternating between them 

Scanner

  • Input device to convert pictures & text into stream of data

Types

1. Drum scanner

  • High quality & price
  • High sensitivity & good signal – to – noise ratio
  • Photo Multiplier (PM) tube – light sensing
  • Image – spinning drum (captures shadow info) – transform to visible region

2. Flatbed scanner

  • Material kept on flat bed of glass
  • Light source & CCD (Charge coupled device) mounted on carriage
  • CCD – converts light to electric pulses
  • Scanning head (with CCD) moves across pictures

3. Sheetfed scanner

  • Paper is pulled over scan head
  • Small Size 
  • Improper Mechanism can skew the paper

4. Hand held scanner

  • Held in hand and moved over document sliding over it
  • Low cost
  • Portability
  • Poor quality

Digital camera

  • Captures instant digital images on internal memory/floppy – interface to PC – transfers to hard disk
  • Lens – focus image
  • CCD – primary sensing
  • CCD array of tiny photo transistors arranged in grid

Block diagram of a digital camera

DVD (digital versatile disk)

  • Storage capacity 17 GB
  • Uses MPEG & Dolby compression tech – ideal multimedia peripheral device
  • High quality video & audio
  • Distance  between  track – less than half that in CD
  • Pits – smaller than in CD
  • Laser spots ‘ve to be smaller – reduced wavelength.