Virtual memory is typically implemented based on at least one of two principle techniques: demand segmentation and demand paging.
Demand segmentation is a technique in which locating computer objects is determined by criteria applied only at the moment of need. Employing primary and secondary storage devices, this technique allocates memory segments as they are required. Concurrently, control software manages the availability of memory segments and connects each incoming module to its originating program according to its function within the IT configuration. A control routine then links the internal and external modules, managing while processing both permanent and transient objects as necessary.
“View Part I of the Managing the Growth and Impact of Virtual Machines and Memory series here“