KnowledgeBase Archive

An Archive of Early Microsoft KnowledgeBase Articles

View on GitHub

Q22523: Windows Does Not Support Real-Time Programming

Article: Q22523
Product(s): Microsoft Windows Software Development Kit
Version(s): WINDOWS:3.0,3.1
Operating System(s): 
Keyword(s): kb16bitonly
Last Modified: 06-NOV-1999

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft Windows Software Development Kit (SDK) versions 3.0, 3.1 
-------------------------------------------------------------------------------

SUMMARY
=======

In no sense can Microsoft Windows be considered a "real-time" system. It is a
message-driven, event-polling system, with nonpreemptive scheduling. The
following is additional information:

1. It is possible to write a Windows-based application that sits on some
  interrupt in order to watch board-level activity. In general, this facility
  is used by manufacturers of boards to write drivers that watch and respond to
  interrupts used by the board. It is extremely dangerous to allocate/sit on
  any interrupt used by Windows itself (keyboard, mouse, etc.).

2. Dedicated systems (those that will not run general-purpose Windows
  applications) may sit on the timer interrupt, as long as Windows is
  eventually notified of the timer ticks. Because of the nonpreemptive aspect
  of the Windows system, it is insensitive to delays in the arrival of timer
  ticks. Trying to run more than one time-critical application that sits on the
  timer interrupt is likely to fail.

3. You must arrange for a Windows "library" of routines to provide access to
  information available from a board. The issue is one of how to divide the
  work between the following portions:

  a. The driver portion, which watches the interrupt, logs data, and notifies
     clients [through PostMessage()] of the availability of data

  b. The client portion, which obtains data from the driver portion, and
     processes, displays, and stores data

  Drivers can be implemented as Windows libraries, and clients of the device can
  be implemented as Windows-based applications. The driver portion can be made
  NEAR real time; the application portion is going to be message driven.

Additional query words: 3.00 3.10

======================================================================
Keywords          : kb16bitonly 
Technology        : kbAudDeveloper kbWin3xSearch kbSDKSearch kbWinSDKSearch kbWinSDK300 kbWinSDK310
Version           : WINDOWS:3.0,3.1

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.