Introduction to CDROM

1
Introduction to CD-ROM

• CD-ROM Compact Disc, Read-Only Memory
• Store digital data rather than digital audio
• Read-only, as publishing medium
• 600MB

2
Short History of CD-ROM

• 1960s/70s videodisk to store movie on disc
• LaserVision as the result of videodisk
• Early 1980s store digital data on LaserVision
  (analog form, no standard)
• 1984 CD audio by Philips and Sony as standard
  (digital format)
• 1985 CD-ROM
• 1986 file system standard of CD-ROM
• Today Recordable-CD, DVD

3
Physical Organization of CD-ROM

• Master disc glass, coating changed by laser
  beam, pits and lands
• Read CD-ROM using high- and low-intensity of
  reflected light to reconstruct the original
  digital information
• Encoding 1s are represented by pit/land or
  land/pit transitions, 0s by the run length
  between transitions.

4
EFM Coding

• EFM - Eight to Fourteen Modulation
• Look-up table

Decimal Original Translated value bits bits 0 0
0000000 01001000100000 1 00000001 10000100000000
2 00000010 10010000100000 3 00000011 10001000100
000 4 00000100 01000100000000 5 00000101 0000010
0010000 6 00000110 00010000100000 7 00000111 001
00100000000 8 00001000 01001001000000
5
CLV vs. CAV
Constant angular velocity
Constant linear velocity
6
CLV Addressing

• Sector-addressing schema
• Each second of playing time is divided into 75
  sectors.
• MinuteSecondSector (162034)
• 60Minutes, 75Sectors/second, 2KB/sector
• 60 x 60 x 75 x 2 540000 KBytes
• 600MB with more than 70 minutes playing time

7
Structure of a Sector

• 2 Bytes to store one sample frequency
• Sample 44100 times per second
• Stereo sound
• 2 x 44100 x 2 176400 Bytes per second
• 176400 bytes into 75 sectors
• 2352 bytes per sector

8
Structure of a Sector
276 bytes error correction
12 bytes sync
4 bytes sector ID
2048 bytes user data
4 bytes error dection
8 bytes null
Totally 2352 bytes per sector
9
Strengths and Weaknesses

• Seek performance - chief weakness
• Data transfer rate - 150KB/sec.
• Storage capacity - 600MB
• Read-Only access - using to design and optimize
  the file system
• Asymmetric writing and reading - writing once,
  reading many times