The use of virtual memory is not visible to the PC user. Which means while working at the computer we will not know whether the virtual memory is being used as there will be no indication.
The reason will be obvious if you know how virtual memory functions. Usually the RAM memory in computers are now either 256 or 512 MB. Some computers also have 1Gb RAM memory.
But this RAM size is not sufficient for most of the tasks that we do in computers. For example after we start the computer and open MS Word and MS outlook, then the RAM memory is occupied by these applications. Therefore if we open more applications without closing the existing applications then the RAM memory is not enough.
While opening another application, the operating system will see which are the applications currently not in use and then move those unused applications to the hard disk temporarily. Therefore temporarily the RAM memory is free and can be used by this new application. This happens automatically by the operating system and therefore not visible to the PC user. This is called virtual memory.