Chapter 6 - Exercises

1. [10 points] What is memory mapped I/O?
An I/O scheme in which portions of address space are assigned to I/O devices, and reads and writes to those addresses are interpreted as commands to the I/O device

2. [10 points] Why is DMA an improvement over CPU programmed I/O?
When CPU programmed I/O is used the CPU is usually fully occupied for the entire duration of the read or write operation and is unavailable to perform other work. With DMA the CPU initiates the transfer, does other operations while the transfer is in progress, and receives an interrupt form the DMA controller when the operation is complete. This frees up the CPU for other tasks.

3. [10 points] When would DMA transfer be a poor choice?
When the amount of data transferred between memory and the I\O device is small. In this case the work to set it up would be more than the benefits of having it.

4. [15 points] Mention two advantages and disadvantages for using a single bus as a shared communication link between memory, processor and I/O devices.
Advantages: versatility and low cost

Disadvantages: communication bottleneck 5. [15 points] 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.
-8 + (.5*60*1000/7200) + (512/20*2^20) * 1000 + 2 = -14.17 ms 6. [10 points] Discuss why RAID 3 is not suited for transaction processing applications. What kind of applications is it suitable for and why?
RAID 3 is not suited for transaction processing applications because reads and writes go to all disks in the group. RAID 3 is suitable in applications with large data sets, such as multimedia and some scientific codes. 7. [15 points] How many times can you store a 4MB song at your 1GB NOR flash memory in Figure
6.7 before the first wear out if wear leveling working ideally?
100000 * (1024/4) = 25,600,000

8. [15 points] Section 6.7 focuses on transactional processing as an example of a disk IO intensive application. Give another example of a disk IO intensive application compare and contrast the performance requirements and consider how different disk implementations (magnetic media, flash memory, or MEMS device) can be more or less appropriate for different applications.
Streaming media is an IO intensive application. Since the access is linear, magnetic media would best take advantage of spatial locality. MEMS and flash memory would not benefit as much from spatial locality.