Wednesday, June 13, 2012

Glossary on CD

Sync
Sync (sync code) the 12 byte area in the sector contains the sync signal. Except for the first and last byte area, the rest parts are all 00. (Audio CD has different sync code than others).


Address format

Min S Min/S
1 1 1
Standard:00~74, max:99 00~59 00~74

The address and intervals between Optical track rails are indicated by time. One second is 75 sectors and their code is from 00 to 74.Each number will be separated by a colon, such as 12:02:24.

Sub-Codes channel or sub-channel
In audio CD, the 98 bytes sub-codes channel is divided into eight sub-channels such as P, Q, R, S, T, U, V, and W. Each sub-channel is 98 bit.

Sub-channel P is to show the start point of audio data.
Sub-channel Q with 98 bit is divided into A, B, C, D, and E five areas.
Area A B C D E
Bit 2 4 4 72 16

A: 2 bit, sync control.
B: 4 bit, data type symbol.
C: 4 bit, the data symbol of the next area D.
D: 7 bit, data of Q sub-channel. In the boot area of CD, there is a table of contents.The rest area of the CD contains the current play time.
E: 16 bit, used for error checking.CRC, (Cyclic Redundancy Code).
Sub-channel R to W: They are not used in common audio CD, they are filled with 0.In CD - Text discs, they are used to record the author, song name, singer team. This additional information can not be read in CD player but they can be read by computer.
In data CD, the sub-channel is 12 bytes and each sector has eight sub-channels: P, Q, R, S, T, U, V and W. Sub-channel P and Q contain data of position and time. Sub-channel R to W can be used to store user's data. Each CD can store at most 20 MB of data. CD-G is the CD disc to store image data.

Cross-Interleaved Reed-Solomon Code
This is the revise code of audio CD. They are set between frames (Q checkout) and at the end of frames (P checkout).

EDC
Error Diagnosis Code
Gap:
The gap between Optical tracks can be divided into:
Post-gap:
At the end of the CD or a rail, there is a short gap (Commonly 2 seconds). Post gap has the same format with the current rail to ensure the readability of data before the change of rail.
Pre-gap:
Before each rail, there is a short gap, commonly 2 seconds. Pre-gap has the same format with the new rail to make the CD-ROM have enough time to adjust for the read of new rails.
Packet:
It is a data storage unit of 64 K bytes that is defined in the Yellow Book.
Close Disc (Finalize Disc):
It is to set the CD-R disc as no longer to write in, even if the disc is not full-written.
Close Session (Fixation):
After the writing of each session there is a writing of lead-in and lead-out with the action of close session, which will determine whether the disc can be continued to writing. If the data is not processed by close session action, it can be only read by CD burner but not CD-ROM.

TOC (Table of Contents):
Content indicates the information about disc and rails. During the process of close session, content shall be written into the Q sub-code channel in the Lead-In Area. It shall contain the number of Optical tracks, the starting and end address of rails, the total length of the CD and so on. 



More Details: http://www.powerdatarecovery.com/cd-dvd-resources/glossary-on-cd.html

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