Dynamic linking and static linking

*   A dynamicllay linked executable is smaller than its statically
   counterpart.  It saves disk and virtual memory, as libraries
   are only mapped in to the process when needed.

*   All executables dynamically linked to a particular library share
   a single copy of the library at runtime.  The kernel ensures that
   libraries mapped into memory are shared by all processes using
   them.  This provides better I/O and swap space utilization and
   in sparing of physical memory, improving overall system throughput.

*   Dynamic linking permits easy versioning of libraries.  New libraries
   can be shipped; once installed on the system, old programs
   automatically get the benefit of the new version without needing
   to be relinked.

*   Finally (much less common), dynamically linking allows users to
   select at runtime which library to execute against.  It's possible
   to create library versions that are tuned for speed, or for
   memory efficiency, or that contains extra debugging information,
   and allow the user to express a preference when execution takes
   place by substituting one library file for another.