Information on an optical volume is organized into units called directories and the basic element of optical storage is the optical file.
A directory is a logical partition that can contain files and other directories called subdirectories. Every volume contains at least one directory called the root directory. You are not required to have other directories below the root directory. Directories are a convenient way to keep files organized.
Any data that is available to application programs can be stored in or retrieved from optical files in the form of a data stream. Optical files have the following characteristics:
