How does virtual memory move program data between RAM and a hard disk?

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Virtual memory enables a computer to run programs that require more memory than is physically available in RAM. It achieves this by creating a large address space for programs, where only a portion of the code and data resides in main memory at any given time.

The system manages the movement of data between RAM and the hard disk through an automated process:

Block Management: The operating system divides program data into blocks of addresses.
Automatic Swapping: When a program needs data that is not currently in RAM, the system automatically copies the required block from the hard disk into main memory.
Locality of Reference: This process relies on the principle of locality of reference—the tendency of a processor to access the same set of memory locations repetitively over a short period—which ensures that the necessary data is typically available in RAM when needed, maintaining efficient performance despite the speed difference between storage types.1