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Compact Disk Formats

While at the lowest level all CDs record information in the same way, on a spiral track using lands and pits, there are many different types of data that can be placed on a CD. For example, an audio CD contains bits and bytes just like a CD-ROM data CD, but the information is laid out in a totally different manner. These different ways of organizing the ones and zeros on the disk are called CD formats. There are several different formats in use today, with new ones being invented all the time. Some are more popular than others; some require special drives to access them, while others are compatible with each other to some degree.

These formats are basically equivalent to the logical structures and file systems used on hard disks or floppy disks. Unlike those media, CD formats are fixed in terms of how the data is structured, storage capacity, block size, etc. There is no way to "format" a compact disk the way a hard disk or floppy disk is formatted, and there is no concept of partitioning either. The structures are basically the same for each CD that uses that particular format.

The sheer number of different formats, and the fact that some drives will handle certain formats while others will not, makes all of this a rather confusing issue for most people (including myself, at first.) This section describes the different formats and tries to make some sense of them, including looking at cross-format compatibility.

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