Explain the difference between internal and external fragmentation for segmentation/paging and allocation of files on disk.

11.7 Explain the purpose of the open and close operations.

12.1 Consider a file currently consisting of 100 blocks. Assume that the file control block (and
the index block, in the case of indexed allocation) is already in memory. Calculate how
many disk I/O operations are required for contiguous, linked, and indexed (single-level)
allocation strategies, if, for one block, the following conditions hold. In the contiguous-allocation
case, assume that there is no room to grow in the beginning, but there is room
to grow in the end. Assume that the block information to be added is stored in memory.
a. The block is added at the beginning.
b. The block is added in the middle.
c. The block is added at the end.
d. The block is removed from the beginning.
e. The block is removed from the middle.
f. The block is removed from the end.

12.5 Consider a system that supports the strategies of contiguous, linked, and indexed allo-cation.
What criteria should be used in deciding which strategy is best utilized for a
particular file?

13.8 How does DMA increase system concurrency? How does it complicate hardware design?

14.2 Suppose that a disk drive has 5000 cylinders, numbered 0 to 4999. The drive is currently
serving a request at cylinder 143, and the previous request was at cylinder 125. The queue
of pending requests, in FIFO order, is
86, 1470, 913, 1774, 948, 1509, 1022, 1750, 130
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?
a. FCFS
b. SSTF
c. SCAN
d. LOOK
e. C-SCAN

14.17 The term “fast wide SCSI-II” denotes a SCSI bus that operates at a data rate of 20 megabytes
per second when it moves a packet of bytes between the host and a device. Suppose that
a fastwideSCSI-II disk drive spins at 7200 RPM, has a sector size of 512 bytes, and holds
160 sectors per track.

a. Estimate the sustained transfer rate of this drive in megabytes per second.
b. Suppose that the drive has 7000 cylinders, 20 tracks per cylinder, a head switch time
(from one platter to another) of 0.5 millisecond, and an adjacent cylinder seek time
of 2 milliseconds. Use this additional information to give an accurate estimate of the
sustained transfer rate for a huge transfer.
c. Suppose that the average seek time for the drive is 8 milliseconds. Estimate the I/Os
per second and the effective transfer rate for a random-access workload that reads
individual sectors that are scattered across the disk.
d. Calculate the random-access I/Os per second and transfer rate for I/O sizes of 4
kilobytes, 8 kilobytes, and 64 kilobytes.
e. If multiple requests are in the queue, a scheduling algorithm such as SCAN should
be able to reduce the average seek distance. Suppose that a random-access work-load
is reading 8-kilobyte pages, the average queue length is 10, and the scheduling
algorithm reduces the average seek time to 3 milliseconds. Now calculate the I/Os
per second and the effective transfer rate of the drive.