Under ISO 9660 standard, there are three interchanges. Only the first interchange can support most main systems, the first layer requires that the data of each file shall be stored on the CD without any intervals. The content of files can not be separated or staggered. The name of files should obey the roles, it must belong to the character set from A to Z, 0 to 9 and "_", moreover, it shall fit for the regulation of DOS. It should have an eight character primary filename and a 3 character sub ordinate file name.
The second layer can use any character as file name which includes the 8 plus 3 length file name, but the content of files should not have any intervals or staggering or segregation. The third layer has no limitations. In the above three layers, ISO9660 file system can not use a directory structure more than 8 layers.
This is the file system defined by Microsoft which can support systems advanced than Win 9x.It can be used during the process of backing up Win 9X to CD. It is the extension of ISO 9660 file system. Under Win9x system, it can display long file name, at most 64 characters, no more than 120 characters including the path.
It is the early stage of 8 plus 3 format with a file name of at most 8 characters.
Romeo support Win9x, WinNT, and Win 2000 to show long filename at most 128 characters.
Rock Ridge is the extension of ISO-9660 that supports uppercase and lowercase, symbol character, long file name, and directory more than 8 layers. As it is compatible with ISO-9660, even if the system can not support Rock Ridge, but Rock Ridge can be checked by ISO-9660. Rock Ridge is a file system that can make CD-ROM compatible with UNIX file system, So it is widely used in CD-ROM under UNIX system.