CD Technology

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CD Technology
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Development

• Developed in 1978 by Philips and Sony
• CD-ROM
• compact disk read only memory
• First used 12 platters
• Current standard size is 4.72 platter
• CD-R stores data in a spiral pattern, center out
  to edge and uses a systems of pits and lands.

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Typical Store Bought CD
Stamped from a master CD
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How Data is Read from a CD
Laser light is sent thru a prism Laser moves to
areas of the disc If it hits a pit, light is
dispersed reads a 0 data value If it hits a
land, light is reflected back to a photocell and
turned into electrical energy reads a data
value of 1
LASER
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Typical CD-R
Compact Disc Recordable CD-WORM write once
read many
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Typical CDRW
Compact Disc ReWritable
POLYCARBONATE MATERIAL
Center of CD
LASER
POLYCRYSTALLINE STRUCTURE
Write Laser uses 2 states High Heat 935F
to1292F -polycrystalline loses reflective
quality Low Heat 392F -polycrystalline
changes back to reflective
The reflective qualities of the surface can be
arranged an rearranged using the high and low
heat into a state similar to the land and pit
technique
Composite silver-indium-antimony-tellurium
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Important Specifications

• Data Transfer Rate (KBps MBps)
• Speed at which data can be transferred in a given
  time
• Access Time (ms)
• Time it takes to send the get command to when the
  first data is read (average)

40X drive spins 40 times faster than a 1X drive
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CD Format Standards

• High Sierra Format
• Organization of the information
• Track 1 identifies the CD as media
• Synchronizes the drive mechanism
• Identifies the directories on the volume
• Reads the Volume TOC that tells how data is laid
  out on the disc
• ISO 9660/ CDFS (CD-ROM File System)
• Used today
• Same as HSF except formatting is different
• Allows long file names
• Files stored in sectors, similar to HDs
• UDF (Universal Disk Format)
• Used primarily in CDRW and DVD
• Allows for bootable disk
• Packet writing similar to way HDs store data

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How Data is Read from a CD

• Constant Liner Velocity (CLV)
• Varies the speed of the CD
• Constant data flow
• To read data from the edges, rpm reduced
• To read data from the center, rpm increased
• Constant Angular Velocity (CAV)
• Constant speed of the CD
• Speed of data flow varies

Data spins faster at the edge
1
Data spins slower at the center
0
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Compatibility Issues

• Old CD drives may not be able to read CDRWs
• New CD Drives can read older technologies
• Should have no trouble reading store bought CDs
  in all drives