Wednesday, June 13, 2012

The logical sector on CD

Logical Sector and Logical Block

Mode 1
Sync Sector head User data EDC ECC
12 4 2048 4 8 276
physical sector 2352 byte
logical sector
2048 byte

A physical sector in CD-ROM has sync, sector head, error checking and revising. The rest parts are using data area with a size of 2048 bytes. 2048 bytes, 2 KB data area can be defined as a logical sector. Each sector has its unique LSN, logical sector number. The physical address of the first logical sector on CD-ROM starts from 00:02:00 with a LSN of 0.

The address of logical sector allows user to define, but it should be 2n, n shall be positive integer.

Each logical sector can be divided into one or several logical blocks. This is very useful to store many small files on the disc. In a logical sector with 2048 bytes, the logical blocks can be 512, 1024 or 2048 bytes. But the size of logical blocks should not be larger than that of the logical sector. Each logical block has a LBN, logical block number. The first logical block with number of LBN 0 is the first block of the first logical sector LSN0, then it goes like LBN1, 2, 3 and so on. In the CD-ROM, all documents and ot
her important data are accord with LBN addressing. 

LSA and LBA:
There are many sectors in the discs; every sector has only one address. Logical sector address needs not to match with the physical address. The address that used by hardware is physical address which is used by operating system as logical address.

Entire sector data(Raw):
Raw does not contain files and folder but includes sync code, Piclist and ECC.
Of the CD burning methods, there is a way called RAW. It refers to burn all the readable data on the CD-ROM, which does not only pick up the user data but also draw the sub-channel data. However, not all CD-ROM supports RAW burning.

Cooking is the process on the information of each sector that indicates the increase of user data such as data address, sync information ECC, data type, instruction and so on. 

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