Answer Happy

a) (5 marks). A file system uses index allocation. The system keeps in main memory only the index block that contains the pointer to the last block read. Other index blocks are in disk. Each index block contains pointers to 127 file blocks, plus a pointer to the next index block (i.e., using linked scheme). Assume the last accessed block was block 200, and the next block to read is block 50 . Compute how many physical blocks must be accessed to read block 50 . Explain your answer. Answer: b) (4 marks). Consider a disk with 200 tracks ( 1 to 200 ) and a seek time of 2msec per cylinder movement. At time 0 there is a set of outstanding read requests, and disk head is positioned over track 119 and moving towards the higher tracks. Consider the queue contains the following requests: 2,156,78,192,19,127,90,100. How long does it take to process the 8 requests using SCAN algorithm? Explain your answer.