The smallest addressable unit on a CD.

For compact discs, the smallest addressable unit of information. The physical size is 2,352 bytes. Often, instead of Block the description Sector is also used.

It is identified by a time given in minutes and seconds and in the case of data through an additional identification character, whereby a Block corresponds to one seventyfifth of a second. On a CD there is a fixed number of blocks. A Block consists of 98 Frames and consists of 3234 Bytes. As a frame contains two times 4 EDC/ECC Bytes respectively and 1 control byte respectively, there are a maximum of 2352 Bytes of further useable data available. For audio CDs (CD-DA) these are fully utilized, for data a further large number of Bytes are lost (Synchronisation bytes, Header and further EDC/ECC Bytes for additional security).

CD-DA (Audio CD): 2352 Data per Block
CD-ROM Mode 1: 2048 Data per Block
CD-ROM Mode 2: 2336 Data per Block
CD-ROM Mode 2, XA Form 1/CD-I: 2048 Data per Block
CD-ROM Mode 2, XA Form 2/CD-I: 2324 Data per Block

A Block can take up 1/75 sec. of audio data, i.e. on a 74 minute CD there are 74*60*75=333000 blocks. On a 74 minute CD can thus save 333000*2352=783216000 Bytes, that is 747MB (see MB = Megabyte). As a data block can only take up 2048 Bytes, on a 74 minute CD it is possible to store 333000*2048=681984000 Bytes = 650MB.

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