Demand Paging

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 :- 

1. reduces the memory requirement
2. reduces the swap time
3. increase the multi programming
4. 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