NT Internals Tips and Trivia

                     Copyright © 1997 Mark Russinovich

                        last updated March 15, 1997

 Miscellaneous NT Information

 Introduction This page is an ever-expanding collection of NT information that we
              accumulate over time. You'll find practical tips as well useless
              trivia, with new items added at the top of the page.

 Never-ending In NT, as with most time-sharing operating systems, threads run in
    Quantum?  turns called quantums. Normally, a thread executes until its
              quantum runs out. The next time it is scheduled it starts with a
              full quantum. However, in NT a thread also gets its quantum
              refreshed every time its thread or process priority is set. This
              means that a thread can reset its quantum by calling
              SetThreadPriority (without changing its priority) before its turn
              runs out. If it continues to do this it will effectively have an
              infinite quantum. Why does NT do this? Its not clear, but it
              appears to be a bug.

   NTOSKRNL's NTOSKRNL.EXE, the core file of the kernel-mode component of Windows
        Main  NT, contains the Cache Manager, the Executive, the Kernel, the
              Security Reference Monitor, the Memory Manager, and the Scheduler,
              among other things, and is in charge of getting NT up and running.
              You may be surprised to know that it has a standard main() that is
              executed when it is loaded by the OSLOADER:
              //
              // NTOSKRNL main
              //
              int main()
              {
                //
                // Fire up NT!
                //
                KiSystemStartup();
                return 0;
              }

        Fault One of the differences I highlighted in my November 1996 Windows NT
 Tolerance on Magazine article, "Inside the Difference Between Windows NT
 Workstation? Workstation and Windows NT Server," was that fault tolerant disk
              configurations are only available on Server. This is because the
              Windows NT disk administrative program, Windisk.exe, checks to see
              if its running on a Workstation, and if so, does not display its
              Fault Tolerance menu, which contains the entries that are used to
              create mirrors and parity striped sets.

              It turns out that whoever wrote the Workstation Resource Kit
              program FTEDIT was unaware of Microsoft's official policy on fault
              tolerance and Workstation: it appears you can use this utility to
              create mirrors and striped sets with parity on Workstations.

       Tuning NT Workstation and NT Server have vastly different performance
  Workstation characteristics due to the internal tuning that the NT operating
          for system, which is identical on both, performs. Most tuning
  Server-like parameters are inaccessible, but a few are located in the Registry.
       Loads  If you are running Server and you double-click on the Server entry
              of the Services tab in the Control Panel's Network applet, you will
              get a dialog that lets you determine what type of application you
              want the machine to be tuned for. Choices let you select between
              "Minimize Memory Used", "Balance", "Maximize Usage for File
              Sharing", and "Maximize Usage for Network Applications". This
              dialog box is not presented on Workstation installations. The
              various selections actually change the values of two Registry
              values:

              HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Memory
              Management\LargeSystemCache

              and

              HKLM\SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters\Size

              This table (which was derived from sessions with NTRegmon) presents
              the settings you should select on a Workstation to achieve the same
              effect you would get using the dialog box were your system a
              Server.

                  Tuning Target     LargeSystemCache    Size
               Minimize Memory Used         0            1
                     Balance                0            2
                   File Sharing             1            3
               Network Applications         0            3

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