Demand Paging ( paging system + swapping):-
Demand paging is used in virtual memory system. Demand paging system is similar to a paging system with swapping. The processes reside in secondary memory & pages are loaded only on demand not a advance. when we want to execute a process , we swap it into memory . rather than swapping the entire process into memory , though we use a lazy swapper. lazy swapper swap the page only when it use needed.
Advantage and Disadvantage :-
- reduces the memory requirement
- reduces the swap time
- increase the multi programming
- page fault is disadvantage of Demand Paging.
Page Fault :- page fault used in the performance measurement .
Performance of Demand Paging:-
Ea = [(p+ page fault time )+((1-p)*ma)]
Ea = effective memory access time
p = probability of page fault
1-p = probability of no page fault
ma = general memory access time