Demand Paging-R.D.Sivakumar

1. Video Lecture and E-Content Created by
R.D.SIVAKUMAR,M.Sc.,M.Phil.,M.Tech.,
Assistant Professor of Computer Science &
Assistant Professor and Head, Department of M.Com.(CA),
Ayya Nadar Janaki Ammal College,
Sivakasi – 626 124.
Mobile: 099440-42243
e-mail : sivamsccsit@gmail.com website: www.rdsivakumar.blogspot.in
DEMAND PAGING

2. Virtual memory is implemented by demand paging.
Demand paging is the combination of paging and swapping.
In this scheme, a page is loaded into the main memory by demand.
A page is note loaded into the main memory from secondary memory until it is
needed.
DEMAND PAGING DEFINITION

3. Page and frame size is 8 KB.
Logical address space is 72 KB.
Available main memory is 40 KB.
EXAMPLE

4. Logical address space is divided into nine pages.
In main memory only five frames are available, the remaining 4
pages are loaded in the secondary storage device.
Whenever those pages are required, the operating system swap in
those pages into the main memory.
In this scheme, the mapping between the pages and frames are
done by “Page map table”.
EXPLANATION OF EXAMPLE

5. The page map table containing of three fields
 Page number
 Frame number
 Valid / Invalid bit
If a page is reside in main memory, the Valid / Invalid bit is set to valid.
If a page is reside in secondary storage, the Valid/Invalid bit is set to invalid.
PAGE MAP TABLE FIELDS

6. Efficient main memory utilization.
ADVANTAGES