Data Structure
ISO 9660 data structures fall into three main categories: the Volume Descriptors, the Directory Structures, and the Path Tables. The Volume descriptor tells where the directory structure and the Path Table are located, the directories tell us where the actual files are located, and the Path table gives us shorts cuts to each directory.
File Location (The Volume Descriptors)
There are currently four types of Volume Descriptors defined in ISO 9660. Only one of these, the Primary Volume Descriptor, is commonly used. The other types are the Boot Record, the Supplementary Volume Descriptor and the Volume Partition Descriptor. The Volume Descriptors are recorded starting at Logical Sector 16 which corresponds to two seconds and sixteen sectors into the CD, or in CD "Atime", 00:02:16. This sector contains file locations represented in LBA (Logical Block Address), the number of Volumes in the current set, the size of a logical block and more importantly a Root Directory Record and Path Table that is desgined for a host to access data location and the actual file. Table 1. is a simply structural diagram of the primary volume descriptor of a CD.
The Primary Volume Descriptor
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Table 1. Simply Structural Digram of the Primary Volume Descriptor
In the Porta-AMP, the first goal of the CDROM Interface Module is to able to read all data from the primary volume descriptor.