2. Why is DMA an improvement over CPU programmed I/O? 3. When would DMA transfer be a poor choice?
4. What is the average time to read or write a 512-byte sector for a typical disk rotating at
7200 RPM? The advertised average seek time is 8ms, the transfer rate is 20MB/sec,
and the controller overhead is 2ms. Assume that the disk is idle so that there is no
waiting time.
5. Disk requests come in to the disk driver for cylinders 10, 22, 20, 2, 40, 6, and 38, in that
order. A seek takes 6 msec per cylinder moved. How much seek time is needed for
(a) First-Come, first served.
(b) Closest cylinder next.
(c) Elevator algorithm (initially moving upward).
In all cases, the arm is initially at cylinder 20.
6. Describe how keyboard software works and which problems does keyboard software
need to handle?