Consider a computer system with ten physical page frames. The system is provided with an access sequence $$\left( {{a_1},{a_2},....,{a_{20}},{a_1},{a_2},...,{a_{20}}} \right),$$ where each $${{a_i}}$$ is a distinct virtual page number. The difference in the number of page faults between the last-in-first-out page replacement policy and the optimal page replacement policy is _____________

A computer system implements $$8$$ kilobyte pages and a $$32$$-bit physical address space. Each page table entry contains a valid bit, a dirty bit, three permission bits, and the translation. If the maximum size of the page table of a process is $$24$$ megabytes, the length of the virtual address supported by the system is _______________ bits.

Consider six memory partitions of sizes $$200$$ $$KB,$$ $$400$$ $$KB,$$ $$600$$ $$KB,$$ $$500$$ $$KB,$$ $$300$$ $$KB$$ and $$250$$ $$KB,$$ where $$KB$$ refers to kilobyte. These partitions need to be allotted to four processes of sizes $$357$$ $$KB,$$ $$210$$ $$KB,$$ $$468$$ $$KB$$ and $$491$$ $$KB$$ in that order. If the best fit algorithm is used, which partitions are NOT allotted to any process?

Assume that there are $$3$$ page frames which are initially empty. If the page reference string is $$1, 2, 3, 4, 2, 1, 5, 3, 2, 4, 6,$$ the number of page faults using the optimal replacement policy is______________.