Examples of this rule may be found in file directories.
File directory can be compressed.
However, a side effect of this design is that reading the file directory of a tape usually requires scanning the entire tape to read all the scattered directory entries.
Occasionally, we would trade file directories, screen images, and illustrations.
In a disk file system there is typically a master file directory, and a map of used and free data regions.
When file backups are made, the tape reel number(s) are recorded in the file directory.
