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Internal Directory Structures
Every file on the hard disk is stored in a directory. A directory is nothing more than a file itself, except that it is specially structured and marked on the disk so that it has special meaning to the operating system. A directory is a table that contains information about files (and subdirectories) that it contains, and links to where the file (or subdirectory) data begins on the disk. The paper analogy would be a table of contents to a book, except that directories of course use a hierarchical tree structure and books do not. (In some ways, a better analogy would be this web site itself; each index frame points to either individual pages, or another sub-index. The PC Guide is hierarchical in the same way as a PC's directory structure, and the home page would be the equivalent of the root directory.)
Each entry in a directory is 32 bytes in length, and stores the following information:
Every regular directory on the disk has two special entries. These are named "." (single dot), which refers to the current directory, and ".." (double dot), which refers to the parent directory. These entries are used for navigation purposes; if you type "chdir .." then DOS will change your current directory to the parent of the one you were in. Note that the root directory has no parent directory, for obvious reasons. :^)