OS/2 Virtual 8086 Problems

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Last update: 6th November, 1995

Here's an unusual OS/2 problem which has been giving me hell for the last month. I couldn't find any information about it in the Pharmacy but did eventually find a possible solution via CIS.

Running applications in a DOS shell resulted in erratic behaviour: programs crashed with GPF errors or Stack Overflow errors, erratic mouse movement and occasional complete OS/2 system lockups. None of these problems occurred running the same applications directly from MS-DOS.

Apparently there is an option in the Control Register of the 486DX-4 and Pentium processors called Virtual Mode Extensions to virtualise the interrupts to a virtual 8086 process. This gives (supposedly) improved performance by speeding up the handling of interrupts, but in my experience causes some DOS applications to behave erratically. Most of my problems were with DPMI applications, including OZCIS (A CIS Navigator). We do a lot of Pascal PMode software development and it crashed a few of our applications regularly as well. OZCIS is a Pascal PMode application so it may be a problem with the Borland DPMI code.

The fix is to add the line:


to your CONFIG.SYS file.

By Steve Agnew

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