Dynamic Loading:

► Routine is not loaded until it is called

► Better memory-space utilization; unused routine is never loaded.

► Useful when large amounts of code are needed to handle infrequently occurring cases.

► No special support from the operating system is required implemented through program design.

Dynamic Linking:

► Linking postponed until execution time.

► Small piece of code, stub, used to locate the appropriate memory-resident library routine.

► Stub replaces itself with the address of the routine, and executes the routine.

► Operating system needed to check if routine is in processes? memory address.

► Dynamic linking is particularly useful for libraries.

Overlays:

► Keep in memory only those instructions and data that are needed at any given time.

► Needed when process is larger than amount of memory allocated to it.

► Implemented by user, no special support needed from operating system, programming design of overlay structure is complex.