Different Default Modes for EMM386.EXE and EMM386.SYS (74851)

The information in this article applies to:
    Microsoft MS-DOS operating system 5.0
    Microsoft MS-DOS operating system 5.0a
    Microsoft MS-DOS operating system 6.0
    Microsoft MS-DOS operating system 6.2
    Microsoft MS-DOS operating system 6.21
    Microsoft MS-DOS operating system 6.22
    Microsoft Windows 3.0
    Microsoft Windows 3.0a

This article was previously published under Q74851


Microsoft Windows version 3.0's EMM386.SYS always defaults to OFF mode, whereas MS-DOS version 5.0, 6.0, or 6.2's EMM386.EXE defaults to ON mode. If you want to compare the behavior of these two versions, either specify ON in the EMM386.SYS command line or specify OFF in the EMM386.EXE command line. The command line arguments ON and OFF activate and suspend the operation of the EMM386.EXE device driver.


Certain non-VCPI aware applications may fail when attempting to enter protected mode with EMM386 enabled. These programs cannot sense that EMM386 has already placed the CPU in protected mode and, thus, cause an "EMM386 Privileged operation error" when they attempt to switch into protected mode.

Applications that function properly with EMM386.SYS but encounter problems with EMM386.EXE may function properly if EMM386.EXE is loaded with the mode specified as OFF.

Modification Type: Major Last Reviewed: 5/10/2003
Keywords: KB74851