Learn in the textbookThe Role and Basic Functions of an OS
DefinitionVirtual memory (仮想記憶) is an OS mechanism that uses part of auxiliary storage as an extension of main memory, making it look as if there is more memory than is physically installed.
ExplanationThe OS moves the parts that do not fit in main memory out to auxiliary storage and brings them back when their turn comes. This swapping lets programs run without being bound by the physical size of main memory, though main memory itself does not grow. When swapping becomes so frequent that processing slows to a crawl, the state is called thrashing (スラッシング).
AnalogyThink of backstage and the stage. Only so many actors fit on stage, but when actors whose scene is over step back and the next ones come on, a play with a large cast can go ahead. With too many changeovers, though, the play stalls.
Memory hookVirtual means "in effect". It is not real main memory, but in effect it works as memory, hence virtual memory.