Computer Science 322 Operating Systems Mount Holyoke College Spring 2008

Agenda

• Announcements
• Lecture assignment recap
• Disks and disk structures
  • disk is arranged into cylinders, divided into sectors, which contain blocks
  • this arrangement is the drive geometry
  • hard to determine the real values in modern disks
  • access: line up read/write head over desired block
  • access time
    • seek time - time to move the read/write head
    • rotational latency - time to get the correct block under the read/write head
• File Systems
  • File system interface
    • file concept
    • file system - organized collection of files
    • file attributes
    • file operations
    • file types
  • Directories - listings of files
    • directory concept
    • directory operations
    • directory organization
      • single-level
      • two-level
      • tree-structured
      • acyclic-graph: links/shortcuts/aliases
      • general graph: upward-pointing links create cycles
    • directory implementation
      • linear list
      • hash tables
• Disks and partitions
  • a system may have multiple disks, each of which contains multiple partitions
  • we create a file system (more later) in each partition
  • mounting: drive letters in Windows, paths in Unix
  • In Unix, a virtual file system layer translates generic paths to the correct partitions (local of varying types, network-accessible)
  • partitioning: why and how?
• File System Implementation Overview
  • want to provide: convenience, protection, efficiency
  • issues:
    • allocation of disk blocks to files/directories
    • track available blocks
    • do this efficiently

Lecture Assignment

Due at the start of class, Wednesday, April 23.

Turn in short answers to these questions. Please turn in a hard copy (typeset or handwritten are OK). We will discuss these questions during class, so no late submissions are accepted.

In class, you were handed a copy of the plot of Delta vs. (1)/(F(Delta)) we generated from the working set simulator. Answer questions 2 and 3 from the Lab 6 description.

Examples

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