Suppose that a disk drive has 5,000 cylinders, numbered 0 to 4,999. The drive is currently serving a request at cylinder 2,150, and the previous request was at cylinder 1,805. The queue of pending requests, in FIFO order, is: 2,069, 1,212, 2,296, 2,800, 544, 1,618, 356, 1,523, 4,965, 3681 Starting from the current head position, what is the total distance (in cylinders) that the disk arm moves to satisfy all the pending requests for each of the following disk- scheduling algorithms? e. C-SCAN f. C-LOOK

5. There are two parts of question 5 a. When can you apply the queue data structure to real-life? Given an example to explain it. b. Can the stack policy apply to a set of documents that wait for printing? The answer is yes or no? Submit P Type here to search Prt Scn W E R

Subject: Operating Systems

Problem 2. In Project 6 you are required to use pthreads condition variables and mutexes to synchronize accesses to shared variables in your priority queue implementation. Ben Bitdiddle wants to try (on his own) to do it using semaphores instead. As in Project 6, the “next" operation returns the highest-priority item in the queue; if the queue is empty, it blocks until the queue becomes non-empty. The “insert" operation places an item in the queue, and if the queue went from empty to non-empty, it signals any waiting threads. Ben's implementation uses a (global) semaphore to count the number of items in the queue, and uses the Bryant and O'Hallaron "P()" and "V()" wrapper functions (see text) to decrement and increment it. He declares a global sem_t list_size and initializes it with sem_init(&list_size,0,0). The global variable list_head points to the first item in the list and is initially NULL. a. In Ben's first attempt, the pq_next() function does this: P(list_size); // block until…