• CD-ROM's store computer data
• CD-ROM's  are very similar to audio CD's, but have two important differences
• Data on CD-ROM discs is divided into sectors containing user data and additional error codes
• Data are contained in files- therefore a file system is needed to easily access these files

2.  Sectors:

• Equivalent to audio frames
• At normal play-back speed (1x), 75 sectors are read per second
• For 2x speed, 150 sectors/second, and so on
• Each sector needs to have header data and error conversion codes.  Two modes for doing this:

Mode 1 is intended for the storage of computer data.  The header contains mins, secs, sectors and the mode(1).  The ECC= Error Correction Code, and the EDC=Error Detection code.  Together the ECC and the EDC provide extra protection for correction digital storage.

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MODE 2:
 

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Mode 2 is mainly used for CD-ROMXA. Its main feature are the two forms instead of just one.  In form 2 there is no error correction.  This form is used for video and audio where errors can be concealed.  In the subheader, information related to the parameters (data type) is stored.

3.  Capacity of CD-ROM:

Mode 1: 2048bytes per sector times 656MB = 336,100 sectors

Mode 2:2048 or 2324 bytes per sector (form 1 or 2) higher capacity than Mode 1
**based upon a single track CD-ROM, for a CD-ROM with more than one track, capacity is reduced

4.  CD-ROM Formats:

1. PC CD-ROM - mode 1, most common, for win95, long file name

2. MPC - mode 1, multimedia PC configuration

3. Mac CD-ROM- mode1, Mac operating system

4. Mixed Mode- mode 1, audio and data combination

5. Photo/Video CD's- mode 2, CD-i bridge format

6. CD-Extra- Mode 2, NEW audio/data mixed mode

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Last edited on May 14, 2000