Question

operating System Concepts, 8th Edition. John Wiley & Sons. By Silberschatz

1. Draw a diagram showing how an application requesting memory causes a page fault and how the data is brought into main memory and sent to the CPU.

Answer 1

Steps:

=>Whenever the requested item is not present in the main memory page fault will occur

=> there is an internal table in CPU called page table, it checks whether the reference made by the user is valid or not.

(the page table maintains the reference of all data item, it matches the reference of request and its table)

=> if the page table returns invalid the process will terminate there itself. ( it returns requested data not available)

=> if, the page table returns valid(valid means there is no problem in accessing that data item), it means the requested data item is present in secondary memory, but it is not loaded.

=> now loading process take place, for that..it is done by the operating system.

=>the OS takes over the control and locates the data item in secondary memory

=> a free frame should be located in the primary memory.

=> the data is now updated into the the physical or primary memory, and page table is updated.

=> the requested data item is provided to application.

Example:

Secondary storage Primary memory Or RAM V requested A data item is fetched Load A Page table that is maintained by CPU free frame

We can uderstand the process from above diagram:

The application stack, needs a dta element A, from memory so it requests it.

1. it checks the page table, whether the data item is present , but the page table returns 'i' which means data item is not present in main memory.

2. whenever i is raised by pagetable, The operating system(OS) takes over control using 'trap' command.

3.OS checks and finds the data item in secondary memory.

4. the data item is transfered to the free frame in main memory.

5. the page table is updated with the reference of new data item.

6. instruction is executed.

Hope this helped , dont forget to like :-)