Single-Level Directory

• The simplest directory structure is the single-level directory. All files are contained in the same directory, which is easy to support and understand (see Fig. 11).

  Figure 11: Single-level directory.

  
• On early personal computers, this system was common, in part because there was only one user. The world's first supercomputer, the CDC 6600, also had only a single directory for all files, even though it was used by many users at once.
• A single-level directory has significant limitations, when the number of files increases or when the system has more than one user.
• Since all files are in the same directory, they must have unique names. If two users call their data file $test$, then the unique-name rule is violated.
• Even a single user on a single-level directory may find it difficult to remember the names of all the files as the number of files increases.