What is virtual memory?

Virtual memory is a memory management technique that allows the operating system to use a portion of the hard disk space as if it were additional RAM. This process helps to extend the apparent amount of usable memory beyond the physical limits of the installed RAM. When the system runs out of physical memory, it can temporarily move inactive data or programs from RAM to a designated area on the hard disk known as the swap file or page file.

This functionality is vital for multitasking, as it enables more applications to run simultaneously than what the physical memory alone would support. By effectively creating an illusion of a large memory pool, virtual memory enhances the system's performance and usability, facilitating better management of applications and workloads.

The other options describe different concepts unrelated to the function of virtual memory. For instance, a physical memory upgrade directly adds more RAM to the system, while features protecting against unauthorized access pertain to security measures. External storage refers to additional devices used for data storage, distinct from memory management techniques.