CS 3733 Operating Systems

Read Chapter 23 of SG

• System overview: (SG Figure 23.1)
  • Designed by David Cutler - principal DEC VAX/VMS OS designer
  • Unicode is NT's native character set (See Unicode: the World's Alphabet and Unicode Consortium web sites for more information).
  • Designed around HAL = hardware abstraction layer.
  • I/O drivers are allowed to bypass HAL.
  • Other major kernel mode components are: the Executive and the Kernel.

• NT Kernel
  • Object oriented - An object type has a set of attributes (data values) and methods (functions that operate on attributes)
    • Dispatcher objects: control dispatching and synchronization
      • events (record event occurrences to synchronize with an action)
      • mutants (provide kernel-mode or user-mode mutual exclusion with ownership)
      • mutexes
      • semaphores
      • threads
      • timers (signal timeouts)

    • control objects:
      • asynchronous procedure call - break into executing thread and call a procedure
      • interrupt object - binds ISR to interrupt source
      • power notify object - call routine after power failure
      • power status object - check for power failure
      • process object - virtual address space and control info to execute threads in a process
      • profile object - measures amount of time used by block of code

  • Kernel dispatcher:
    • Thread states: ready, standby, running waiting transition, terminated
    • Scheduling: multi-level feedback queues
      • 32-level priority (real-time class 16 to 31; variable class is 0 to 15)
      • Traverses queues from highest to lowest
      • If no ready thread, runs the idle thread
      • If a thread's quantum expires, its priority is decreased, but never below base.
      • When released from wait state, gets a priority boost that depends on the type of wait.
      • Preempts for higher priority jobs.

  • Exception Dispatcher:
    • used for things that can't be handled by simple trap handlers
    • creates an exception record
    • tries to locate the right handler - if not found get blue screen

  • Interrupt dispatcher:
    • Either calls an ISR in a device driver or an internal kernel routine
    • Maps hardware interrupts into a standard set
    • Serviced in priority order (SG Figure 23.2)
    • Uses a dispatch table to bind interrupt level to ISR
    • Deferred procedure call object (DPC) contains address of function to be executed and generates a DPC interrupt. Usually higher priority than system calls.
    • Asynchronous procedure call (APC) - allows a thread to set up a procedure call that will happen sometime in the future. (Similar to but more general than asynchronous I/O).

  • Multiprocessor synchronization: uses a spin-lock in shared memory (like a test and set).

• Executive:
  • Services:
    • Object Manager: manages objects such as directories, symbolic links, semaphores, event objects, process and thread objects, port objects and file objects
      • standardized interface with the following methods:
        • open method returns a handle to object
        • create
        • close
        • delete
        • query name - give name from object (e.g. get filename back)
        • parse - find object from name
        • security - change protection
      • Naming
        • Global naming in a directory
        • Can be permanent or temporary
        • Structured like path names

      • Handles
        • Open
        • Create
        • Receive a duplicate from some other process
        • Inherit from a parent

      • Authentication
        • User gets an access-token object at login
        • The access-token object contains IDs, privileges and a default access control list
        • each object has an access control list
        • access is authenticated when object is opened so NT services that use pointers rather than handles bypass security

    • Virtual-Memory Manager
      • Page-based 4 KB page size
      • 32-bit address space (upper 2 GB for kernel)
      • Two-step process:
        • Reserve memory
        • Commit allocation
      • Shared memory
        • Parent can reserve right to access VM of child
        • Process share memory by getting a handle to same memory space
        • Section object - block of shared memory, process only needs to map a portion called a view -- allows a process to access an object too large to fit into memory.
      • Multilevel page table:
        • 1024 entry page directory
        • Each entry in page directory is a ponter to a page table of 1024 entries
        • Each PTE points to a 4KB page
        • Low 12 bits of PTE (5 bits of protection, 4 bits specify which paging file, 3 bits specify page state)
        • Page state:
          • valid - in use by active process
          • free - not referenced in a PTE
          • zeroed - free page that is zeroed out
          • standby - page that has been removed from process working set
          • modified - has been written by not modified
          • bad - unusable because of a hardware error

      • Replacement
        • Takes first from from free list and replaces it
        • Also faults adjacent pages
        • If no frames on free list, uses per-process FIFO
        • Processes start with default working set of 30 pages
        • NT periodically tells a valid page if if no faults occur, working set reduced by 1
        • Processes with a lot of faults may get allocation increased.

    • Process Manager - doesn't keep parent-child relationships
    • Local Procedure Call (LPC)
      • uses message passing
      • server publishes visible connection-port object
      • client opens handle to port and sends a connection request
      • server creates a channel and returns a handle
      • channel consists of pair of ports for two way communication
      • accept callbacks so that they can take requests rather than replies
      • three types of messages:
        • small (upto 256 bytes) - uses ports message queue for storage
        • larger - shared memory object is created and message contains pointer to memory object
        • quick LPC
          • used for Win32 subsystem
          • server ents up dedicated thread, 64 KB section object and event-pair object to notify server when client has copied a message or vice versa.

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  Skill: Have a basic overview of NT design

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  Revised 4/24/98

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