DOCUMENT:Q78609 17-DEC-2000 [msdos] TITLE :Troubleshooting HIMEM.SYS PRODUCT :Microsoft Disk Operating System PROD/VER:MS-DOS:5.x,6.0,6.2,6.21,6.22 OPER/SYS: KEYWORDS: ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft MS-DOS operating system versions 5.0, 5.0a, 6.0, 6.2, 6.21, 6.22 ------------------------------------------------------------------------------- SUMMARY ======= This article describes how to troubleshoot HIMEM.SYS. MORE INFORMATION ================ HIMEM.SYS Auto-detection Strategy --------------------------------- Selection of A20 handlers is based on an auto-detection strategy. HIMEM runs through all of its auto-detection schemes trying to find a match. If found, the particular handler is installed. If no match is found, the default A20 handler is installed. There are a number of different auto-detection routines and these are done in a certain order. Sometimes, due to the non-standard nature of the machine, the auto-detection fails and the default handler is installed. However, the default handler does not work too well. In this case, the user has to give an explicit override and ask HIMEM to install a particular A20 handler. In other cases, HIMEM may identify a machine incorrectly and install the wrong A20 handler. Basically, the machine identification strategies are not, and cannot be, foolproof. Troubleshooting this kind of problem can be done only by trial and error. HIMEM.SYS and /INT15=xxxx Switch -------------------------------- When HIMEM starts, it grabs all of the INT 15h memory present in the system. It then provides extended memory to different applications via the XMS interface. However, there are some old applications that do not understand XMS and need some INT 15h memory to be present. To support these applications, HIMEM.SYS provides a /INT15=xxxx switch on its command line. Using this, you can ask HIMEM.SYS to leave xxxx Kbytes of extended memory on the INT 15h interface so that applications can use INT 15h to allocate extended memory. For example, Pharlap DOS Extender needs this switch. The use of this switch is documented in the version 5.0 "Microsoft MS-DOS User's Guide and Reference." Additional query words: tshoot 6.22 5.00 5.00a 6.00 6.20 ====================================================================== Keywords : Technology : kbMSDOSSearch kbMSDOS621 kbMSDOS622 kbMSDOS620 kbMSDOS600 kbMSDOS500 kbMSDOS500a Version : MS-DOS:5.x,6.0,6.2,6.21,6.22 ============================================================================= 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. Copyright Microsoft Corporation 2000.