1.  Storage Area:

The area data is stored in CD's is divided into three areas:
1. Lead -In Area:
    The lead in contains digital silence in the main channel and a Table of Contents in the subchannel Q. The Table of Contents (TOC) contains the time code for each track, and the last time code is for the lead out ( hexadecimal code=AA).
2. Program Area:
        The program area contains up to 76 minutes of data divided into a maximum of 99 tracks.
3. Lead-Out Area:
        The lead out area contains digital silence and the code for the end of the CD program.

Subcode Channels:

In addition to the main data channel there are 8 subchannels that are interweaved with the main channel.

P-Channel: Indicates the start/end of each track, originally designed for simple audio players which did not have full Q channel coding.

Q-Channel: Time codes, Table of Contents, track type, catalogue number

R through W channels: Subcode graphics (CD-G), and CD-text , * allow graphics to be displayed while music is being played, only 3% of capacity of the CD is used for these channels

Error Correction:

Two levels of correction are included on a CD because it is impossible to produce a CD without making any mistakes.

1. CIRC (Cross Interleaved-Read Solomon Code):
    An encoder adds two-dimensional parity information to correct information, and then interleaves the data on the disc to prevent burst errors.

2. EFM Modulation (Eight to Fourteen):

• Encodes each 8 bit symbol as 14 bits plus 3 merging bits
• Used to define pits and lands on the CD, since the CD cannot read to "1" in a row
• Land/Pit are each no less than 3 bits and channels are no longer than 11 bits
• Reduces the effect of jittering

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Last edited on May 14, 2000