The main advantage of the overlay technique in memory management is that it…

Concept

Overlaying is a memory-management technique in which a program is split into self-contained modules called overlays, only some of which must reside in main memory at any instant. Mutually exclusive parts of the program share the same physical memory region, taking turns: an overlay is loaded over (replacing) a previous one when its routines are needed.

Application

The total program text may be far larger than the available physical memory, yet only the overlay (or overlays) currently executing plus the resident root must fit. Because inactive overlays are not held in memory simultaneously, the technique lets a program whose full size exceeds the machine's memory still execute within that limited memory.

Example: a 100 KB program on a 60 KB machine. Keep a 20 KB root resident and divide the rest into overlays of at most 40 KB each that never run at the same time; each is loaded into the same 40 KB slot when called, so the program runs despite needing more than 60 KB in total.

Cross-check / Contrast

• Loading a program as a whole is the opposite of overlaying and still requires the whole program to fit in memory — it removes the size advantage rather than providing it.

• Sharing memory partitions among processes is multiprogramming/partition allocation, a separate goal concerning several processes, not enlarging one program's effective space.

• Direct process-to-process communication is interprocess communication, unrelated to fitting one large program into small memory.

Hence overlaying's defining benefit is running a program larger than the physically available memory.