Virtual storage (virtual memory) behavior Under a virtual storage system, which statement describes how primary memory is used?

Introduction / Context:
Virtual storage, commonly called virtual memory, decouples the logical address space of a process from physical memory. The operating system and hardware collaborate to load and evict pages so that programs can run even when their total size exceeds available RAM.

Given Data / Assumptions:

• Paged virtual memory is assumed.
• Page tables map virtual pages to frames in physical memory.
• The working set idea says that only currently needed pages must reside in RAM.

Concept / Approach:

Virtual memory loads only active pages into RAM, keeping inactive parts on secondary storage. Page faults trigger on demand loading, while replacement algorithms such as LRU choose victims to evict. This allows large programs and multiple processes to coexist, giving the illusion of large contiguous memory.

Step-by-Step Solution:

Verification / Alternative check:

Operating systems literature describes demand paging and working set models; tools like task managers display commit versus working set sizes, illustrating that only active portions are resident.

Why Other Options Are Wrong:

a: describes multiprocessing, not virtual storage. b: can be true even without virtual memory and is not the defining behavior. d: good isolation prevents interprogram interference in virtual memory systems.

Common Pitfalls:

Assuming all of a program must be loaded to run; confusing swapping entire processes with paging of small units.

Final Answer:

Only the active pages of a program are stored in primary storage.