2.7.1 Simple Structure
Many operating systems do not have well-defined structures. Frequently, such
systems started as small, simple, and limited systems and then grew beyond
their original scope. MS-DOS is an example of such a system. It was originally
designed and implemented by a few people who had no idea that it would
become so popular. It was written to provide the most functionality in the
least space, so it was not carefully divided into modules. Figure 2.11 shows its
structure.