The techniques which automatically move the program blocks to or from the…

Concept — Virtual memory organisation deliberately separates the address space in which a program is written and executed from the physical main memory actually installed on the machine. The processor issues virtual (logical) addresses; a memory-management unit translates each of them into a physical address, and the operating system automatically transfers blocks of program and data between secondary storage and physical main memory as execution demands them. This automatic block movement is what allows a program larger than the available physical memory to run.

Application — The operative words in the stem are "automatically" and "when they are required for execution": the transfer is performed by the system itself, on demand, without the programmer arranging it. That is exactly the standard textbook statement — techniques which automatically move program and data blocks into the physical main memory when they are required for execution are called virtual-memory techniques. The blank is therefore filled by virtual memory organisation.

Cross-check — the remaining candidate terms each name something narrower or different:

• Paging: a fixed-size partitioning scheme — the address space is cut into equal-size pages and main memory into equal-size frames. It is one mechanism used to implement virtual memory, not the name of the family of transfer techniques.

• Overlays: a programmer-planned scheme that predates virtual memory, in which modules are written to share one region of memory and the programmer codes explicit load points. The movement is arranged by hand rather than performed automatically by the system on demand, so it does not satisfy the stem — and removing that burden from the programmer is exactly why virtual memory was introduced.

• Framing: the division of physical memory into equal-size page frames (and, in networking, the delimiting of a bit stream into frames). It names a division of storage, not a technique for transferring program blocks.

Result — the techniques that automatically move program blocks to or from physical memory as execution requires them are collectively called virtual memory organisation, that is, virtual-memory techniques. This is the standard definition used in Hamacher, Vranesic and Zaky, Computer Organization.