Q08: Disk storage (6 marks)
Consider a disk with a block size of 256 bytes, 1,000 tracks per surface, 100 blocks per track,
20 single-sided platters, a rotational speed of 3,600 revolutions per minute, and an average
seek time of 10 msec. Suppose that a file containing 400,000 records of 100 bytes each is to be
stored on such a disk and that no record is allowed to span two blocks.
- How many records fit into a block? What is the capacity of this disk?
- How many blocks are required to store the entire file?
Assume the data transfer rate is 10 megabytes per second (1 megabyte = 220 bytes), and
the records are stored sequentially. Compute the average time needed to read a block.
Q09: Buffer management (8 marks)
Consider the following page access sequence:
Time 1: Request Page 5, release it, modified
Time 2: Request Page 8, release it, unmodified
Time 3: Request Page 10, release it, modified
Time 4: Request Page 20
Time 5: Request Page 30, release it, modified
Time 6: Request Page 10, release it, modified
Time 7: Request Page 18, release it, unmodified
Assume the buffer content is as shown below after Time 3. Fill in the buffer content for Times
4-7 under the LRU and MRU policies, respectively. Indicate if a page needs to be written back
to the disk when it is replaced.