The most common way to implement virtual memory today is to divide the address space in fixed sized blocks called memory pages. When a process accesses memory at a virtual address, the operating system checks whether the memory page is backed by physical memory (a page frame). If the memory page is not mapped in the main memory, a hardware exception occurs and the page is loaded from disk into memory. This type of hardware exception is called a page fault. This is not an error but a necessary interrupt in order to load data from disk to memory. As you may have guessed though, this is very slow compared to reading data that is already resident in memory.
When there are no more available page frames in the main memory, a page frame ...
