Interview Q&A / Operating Systems

31. What is the dining philosophers problem and how can it be solved?

    Five philosophers sit round a table with five forks, and each needs two adjacent forks to eat. If all pick up their left fork together, everyone waits forever. Solutions include a fork ordering, a limit of four seated, or an asymmetric pickup.

    IntermediateQuick answer1 min read
32. Why do operating systems use multi-level page tables?

    A single flat page table needs an entry for every possible page, even unused ones. A multi-level table splits it into pieces and only allocates the pieces for regions actually in use, saving a large amount of memory.

    IntermediateQuick answer1 min read
33. How does the Banker's algorithm decide whether a resource request is safe?

    It pretends to grant the request, then checks whether some order exists in which every process can still finish with the resources left. If such a safe sequence exists, the request is granted; otherwise it waits.

    AdvancedQuick answer2 min read
34. What is the Test-and-Set instruction and how does it provide mutual exclusion?

    Test-and-Set is a hardware instruction that atomically reads a memory flag and sets it to 1. If it returned 0, the caller got the lock; if 1, someone else holds it. Because it is one indivisible step, two threads cannot both see 0.

    AdvancedQuick answer1 min read