Operating Systems

Operating Systems

1. Supported by

   • Interrupt mechanism
   • Device addressing
     • Numbered
     • Memory mapped
   • Autoconfiguration facilities
   • Autonomous I/O
   • Memory management support
   • Privileged control instructions
   • Timer/instruction counter
   • Time of the day clock
   • Performance assists
   • Support for multiple processors

2. Desirable OS features

   • Efficiency
   • Reliability
   • Resilience
   • maintainability
   • small size

3. Desirable OS characteristics

   • Concurrency
   • Sharing
   • Long term storage
   • Non determinancy

4. Functions

5. Resources managed

   • Memory
   • Access to mouse & keyboard
   • Network access
   • Central processor time
   • Desktop

6. Types of OS

7. Structure of the OS

   • Monolithic
   • Layered
   • Microkernel (client-server)

8. Presents user with a

   • Virtual Machine
     • I/O
       • I/O buffering
         • To allow transfers of arbitrary length
         • Improve throughput
         • Simplify memory management
       • Spooling
     • Memory
       • Virtual Memory
         • Base register
         • Limit register
         • Paging
         • Page Table Entry
           • Page Frame Number
         • Virtual address
           • Page number
           • Offset
         • Paging efficiency
           • Transaction Lookaside Buffer
         • Page replacement strategies
           • FIFO
           • Last used recently
           • Random
           • Least used
           • Not used recently
     • Filing system
       • must provide
         • Device independence
         • Ease of use
         • Efficiency
         • Protection against system failure
       • Srorage may be on
         • Magnetic disks
         • Magnetic tape
         • Optical disks
         • Flash memory
       • Organisation
         • Contiguous
         • Index block
         • File map
       • File directories
         • File access control
           • user/group/world
           • Access Control Lists
         • Management of free space
           • Bit Map
           • "File on their own"
       • Security/backup
         • Periodic backup
         • Incremental backup
     • Protection and data handling

9. Processes & processors

   • Concurrency
     • Mutual exclusion
     • Synchronisation
   • Inter process communication
     • Semaphore
   • Kernel
     • First level interrupt handler
     • Low level interrupt handler
     • Communication primitives
   • Process Control Block
   • Memory management
     • Real address
     • Virtual address

10. Program environment

    • Object modules
    • Absolute and relocatable code
    • Dynamic Link Libraries

11. Resource allocation

    • Allocation mechanism
    • Allocation policies
    • Resource deadlock
      • occurs because of
        • UNSHARABLE resources
        • CIRCULAR chain of requests
        • Resources cannot be PRE-EMPTIED
        • Resources already ALLOCATED while requesting for new one
      • can be solved by
        • PREVENTION
          • Prevent the 4 ocurrance causes
        • RECOVERY
          • Remove resources from one or more processes
        • AVOIDANCE
          • Banker's algorithm
    • Scheduling
      • High-level
      • Intermediate
      • Low-level

12. Remote file access

    • Design issues
      • Naming
      • Communication patterns
      • Software structure
      • workload allocation
      • consistency maintenance
    • Requirements
    • Implementation
      • Stateless file serving

13. File system

    • NFS
    • CIFS
      • SMB protocol
      • Oplocks