Computer Science 330
Operating Systems

Fall 2020, Siena College

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Agenda

• Announcements
  • The next readings/activities from OS zyBook: Chapter 9, due Friday
  • The next Term Project milestone is the progress report due in a week
  • Programming Project 3: The Roger Bacon Shell [HTML] [PDF] accepted through Friday without penalty
  • Final Exam one week from today
  • Lab 8: Working Set Simulation [HTML] [PDF] finish "writeup" for Wednesday
• 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 Implementations
    • want to provide: convenience, protection, efficiency
    • issues:
      • allocation of disk blocks to files/directories
      • track available blocks
      • do this efficiently
  • Disk block allocation methods
    • contiguous allocation
    • extents
    • linked allocation
    • variation on linked: file allocation table (FAT)
    • indexed allocation
      • straightforward implementation
      • linked indexed allocation
      • two-level index
    • Unix inodes
      • a combination of the best features of many of the above
      • set aside special disk blocks called inodes (index nodes)
      • inode has entries pointing to direct file blocks, a single indirect block, a double indirect block, and a triple indirect block
      • a superblock keeps track of inodes and data blocks
      • see /usr/src/sys/ufs/ufs/dinode.h in FreeBSD
    • Concerns: file size limits, fragmentation, overhead, performance
  • Free Space Management
    • bit vector
    • free list

Examples

• https://github.com/SienaCSISOperatingSystems/morelinks-example

Links

• ReiserFS on Wikipedia
• IBM JFS
• FreeBSD Soft Updates
• HPSS