Single-User Allocation
• Drawbacks
• user program is limited in size.
• user program cannot be larger than size of memory
• Solution: Overlays
• user memory space is divided into 2 sections:
• fixed portion: essential program data is loaded and stay
through out duration of execution.
• overlay area: an area where various modules can be assigned
the same region of memory, with a main program responsible
for switching the modules in and out as needed — different
segments of programs can be swapped in and out during
execution.