Virtual memory is an extension of primary storage (RAM) located on secondary storage eg hard disk
In situations where RAM is close to being full, virtual memory can be used so that the computer remains operational
Programs and data not currently being executed are transferred to virtual memory
Programs and data are transferred back to RAM when they are needed
Virtual memory is much slower than RAM (because it has to go back to RAM first) and it's use will impact negatively on system performance (thrashing)
To avoid the use of virtual memory, increase the size of the RAM
