What are Dynamic Loading, Dynamic Linking and Overlays?

Dynamic Loading:

o   Routine is not loaded until it is called

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

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

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

Dynamic Linking:

Linking postponed until execution time.

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

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

o   Operating system needed to check if routine is in processes’ memory address.

o   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.