Question

Which of the following statements is true about paging? Choose all that applies.

• Frame numbers maps pages to physical memory 

• Page table size must be a power of 2 

• Suffers from internal fragmentation 

• Pages size must be a power of 2

Answer 1

True about paging :

3.suffers from internal fragmentation

There are basically two types of non-contiguous memory allocation schemes, viz., Paging and Segmentations. Any fixed-size partition based memory allocation scheme suffers from internal fragmentation. This problem arises when the size of a process is not a whole multiple of the partition size. In such case, for the last portion of the process, we need to allocate an entire partition whose part is only used by the process. Paging is also a fixed-size partition scheme, hence, suffers from internal fragmentation problem. External fragmentation exists when there is enough total memory space available to accommodate a process or part of a process but the available spaces are not contiguous; storage is fragmented into a large number of small blocks of free memory. Segmentation may cause external fragmentation, when all blocks of free memory are too small to accommodate a segment but the sum of the free spaces is larger than the segment size. Hence, paging suffers from internal fragmentation and segmentation suffers from external fragmentation problem. However, paging does not suffer from external fragmentation and segmentation does not suffer from internal fragmentation problem.

4. Page size must be a power of 2  

Recall that paging is implemented by breaking up an address into a page and offset number. It is most efficient to break the address into X page bits and Y offset bits, rather than perform arithmetic on the address to calculate the page number and offset. Because each bit position represents a power of 2, splitting an address between bits results in a page size that is a power of 2.