Computer Science 432/563
Operating Systems

Spring 2016, The College of Saint Rose

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Agenda

• Announcements
  • Office hours will start late tomorrow
  • Programming Project 3: knish: The Knight Shell late clock will start Friday night
  • Term Project, now working toward progress reports
  • Lab 5: Working Set Simulation continues
• Storage Devices
  • Magnetic hard disks
  • Optical disks
  • Flash memory
• Disk Scheduling Algorithms
  • Recall: cost of a disk access includes seek time and rotational latency
  • We wish to minimize seek time by minimizing the distance the read/write head has to move in order to service the incoming requests by reordering requests based on cylinder number
  • This optimization may be done by the disk, the hardware controller, or by the operating system
  • Compare algorithms by examining their performance on a given request queue
  • First-Come First-Served (FCFS)
  • Shortest Seek Time First (SSTF)/Closest Cylinder Next
  • SCAN or Elevator Algorithm
  • LOOK Algorithm
  • Circular Algorithms
  • Comparing Disk Scheduling Algorithms
    • SSTF or LOOK are often reasonable for a default algorithm
    • SCAN and C-SCAN are better for heavily loaded systems where LOOK is unlikely to save much and SSTF runs the risk of starvation
    • performance depends on the frequency and types of requests
    • we may want to consider some of this when we decide how to organize file systems
  • FreeBSD's ufs filesystem uses an elevator algorithm (see /usr/src/sys/ufs/ufs/ufs_disksubr.c)
• RAID
• File Systems
  • File system interface
    • file concept
    • file system - organized collection of files
    • file attributes
    • file operations
    • file types

Lecture 0x13 Assignment

Due at the start of class, Monday, April 11.

Please submit answers to these questions either as a hard copy (typeset or handwritten are OK) or by email to terescoj AT strose.edu by the start of class. Please use a clear subject line when submitting by email (e.g., CS 432 Lecture 0x13 Assignment, Mary Smith). We will discuss these questions at the start of class, so no late submissions are accepted.

The readings for next class are SG&G Chapter 10.

• SG&G Exercise 9.10, p. 472 (2 points)
• SG&G Exercise 9.11, p. 472-3 (6 points)
• SG&G Exercise 9.15, p. 474 (4 points)
• SG&G Exercise 9.16, p. 474 (4 points)
• SG&G Exercise 9.18, p. 474 (4 points)

Links

• RAID on Wikipedia