Interview Q&A / Operating Systems

1. What is thrashing in an operating system, and how can it be prevented?

   Thrashing is when a system spends most of its time moving pages between RAM and disk instead of running programs, because the running processes together need more memory than is available. It is prevented by giving each process enough frames for its working set, controlling page-fault rate, and reducing the number of running processes.

   AdvancedIn-depth4 min read
2. 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
3. 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