IO Systems

• IO systems (Slides)
  • IO Hardware
    • Device features (SGG Ch.13.2)
    • Device abstraction (SGG Ch.13.2.0, Ch.13.3.0-1)
  • Kernel IO subsystem
    • IO interface (SGG Ch.13.3)
    • Scheduling (SGG Ch.13.4.1)
    • Buffering (SGG Ch.13.4.2)
    • Caching (SGG Ch.13.4.3)
    • Error handling (SGG Ch.13.4.5)
  • IO Requests
    • Forms of IO
    • Interrupts (SGG Ch.13.2.2)
    • Polling (SGG Ch.13.2.1)
  • Special Services
    • DMA (SGG Ch.13.2.3)
    • Spooling and device reservation (SGG Ch.13.4.4)
    • Network interface
  • Data structures (SGG Ch.13.4.6)
  • UNIX IO system
    • IO structure
    • Block buffer cache
    • C-lists
    • Raw device access

• Disk management (Slides)
  • Disk scheduling (SGG Ch.13.2)
    • FCFS scheduling (SGG Ch.13.2.1)
    • SSTF scheduling (SGG Ch.13.2.2)
    • SCAN scheduling (SGG Ch.13.2.3)
    • C-SCAN scheduling (SGG Ch.13.2.4)
    • C-LOOK scheduling (SGG Ch.13.2.5)
  • Bad block management (SGG Ch.13.3.3)
    • Manual handling via block allocation (delete from free list)
    • Sector sparing
    • Sector slipping
  • Swap space management (SGG Ch.13.4)
  • Disk reliability (SGG Ch.13.5)

Exam Style Questions

• What do device drivers do in an OS?
• Briefly describe two ways in which an application may cause a device driver to perform IO tasks.
• When an application requests IO activity, how is the request sometimes satisfied without the IO device being used?
• Differentiate between interupt drive IO and polling? In what sort of situations is polling more appropriate than interupt driven IO?
• List the six basic steps in DMA.
• How does DMA improve the performance of a computer system?
• What is the difference between a block device and a character device? Give an example of each.
• What is "buffering"? Give three reasons for an OS to use buffering.
• Differentiate between buffering and caching.
• In what circumstances would an operating system use SPOOLing or device reservation? What is the potential danger of device reservation?
• Explain the differences in an operating system's response between transient and permanent IO failures.

• What is a "block" in an OS file system?
• Define disk bandwidth.
• How can disk scheduling improve OS performance?
• Given the following sequence of disk request track numbers, list the order in which they will be services by the {FCFS,SSTF,SCAN,C-SCAN, LOOK,C-LOOK} disk scheduling algorithm. For each, give the total seek time taken.
  [List of track numbers, make up your own].
• What problems does the SSTF disk scheduling algorithm have?
• What is the weakness of the SCAN disk scheduling algorithm?
• How does the C-LOOK disk scheduling algorithm improve over the C-SCAN algorithm?
• Explain two ways in which RAID technology is used to provide higher disk reliability.