OS 2023-24

Page fault occurs when

• When a requested page is in memory

• When a requested page is not in memory

• When a page is corrupted

• When an exception is thrown

Let the page fault service time be 10ms in a computer with average memory access time being 20ns. If one page fault is generated for every 10^6 memory accesses, what is the effective access time for the memory?

• 21ns

• 23ns

• 30ns

• 35ns

In which one of the following page replacement policies, Belady’s anomaly may occur?

• FIFO

• Optimal

• LRU

• All of the above

A multilevel page table is preferred in comparison to a single level page table for translating virtual address to physical address because

• It reduces the memory access time to read or write a memory location.

• It helps to reduce the size of page table needed to implement the virtual address space of a process.

• 
  It is required by the translation lookaside buffer.

• 
  It helps to reduce the number of page faults in page replacement algorithms.

The essential content(s) in each entry of a page table is / are

• 
  Virtual page number

• Page frame number

• Both

• 
  Access right information

A system uses 3 page frames for storing process pages in main memory. It uses the Least Recently Used (LRU) page replacement policy. Assume that all the page frames are initially empty. What is the total number of page faults that will occur while processing the page reference string given below? 4, 7, 6, 1, 7, 6, 1, 2, 7, 2

• 4

• 5

• 6

• 7

The optimal page replacement algorithm will select the page that

• Has been used least number of times.

• Will not be used for the longest time in the future.

• Has not been used for the longest time in the past.

• 7Has been used most number of times.
  

In a paged memory, the page hit ratio is 0.40. The time required to access a page in secondary memory is equal to 120 ns. The time required to access a page in primary memory is 15 ns. The average time required to access a page is

• 
  105

• 68

• 75

• 78

In the context of operating systems, which of the following statements is/are correct with respect to paging?

• Paging helps solve the issue of external fragmentation

• Page size has no impact on internal fragmentation

• 
  Multi-level paging is necessary to support pages of different sizes

• None

The number of page frames that must be allocated to a running process in a virtual memory environment is determined by

• page size

• the instruction set architecture

• number of processes in memory

• physical memory size