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directory(5) - Unix First Edition Manual Page
11/3/71DIRECTORY (V)

NAME format of directories
DESCRIPTION A directory behaves exactly like an ordinary file, savethat no user may write into a directory. The fact that a

file is a directory is indicated by a bit in the flag wordof its i--node entry.

Directory entries are 10 bytes long. The first word is thei--node of the file represented by the entry, if non--zero; if zero, the entry is empty. Bytes 2--9 represent the (8--character) file name, nullpadded on the right. These bytes are not necessarily cleared for empty slots. By convention, the first two entries in each directory arefor "." and "..". The first is an entry for the directory itself. The second is for the parent directory. The meaningof ".." is modified for the root directory of the master file system and for the root directories of removable filesystems. In the first case, there is no parent, and in the second, the system does not permit off--device referenceswithout a mount system call. Therefore in both cases ".." has the same meaning as ".".

SEE_ALSO file system format
OWNER ken, dmr