The page replacement algorithm decides which memory page is to be replaced. The process of replacement is sometimes called swap out or write to disk. Page replacement is done when the requested page is not found in the main memory $($page fault$).$

There are two main aspects of virtual memory, Frame allocation and Page Replacement. It is very important to have the optimal frame allocation and page replacement algorithm. Frame allocation is all about how many frames are to be allocated to the process while the page replacement is all about determining the page number which needs to be replaced in order to make space for the requested page. If the number of frames which are allocated to a process is not sufficient or accurate then there can be a problem of thrashing. Due to the lack of frames, most of the pages will be residing in the main memory and therefore more page faults will occur.

If the page replacement algorithm is not optimal then there will also be the problem of thrashing. If the number of pages that are replaced by the requested pages will be referred in the near future then there will be more number of swap$-$in and swap$-$ out and therefore the OS has to perform more replacements then usual which cause performance deficiency.

Which of the following statements is accurate regarding the time required to switch between user and kernel modes of execution $($t$1)$ compared to the time needed to switch between two processes $($t$2)?$

a$.$

t$1<$ t$2$

b$.$

t$1=$ t$2$

c$.$

t$1>$ t$2$

d$.$

Nothing can be said about the relation between t$1$ and t$2$