Microsoft DOS EMM386 command

Updated: 05/21/2018 by Computer Hope

About EMM386

EMM386.EXE is an Extended Memory Manager used with Intel 80386 and above processors. This program allows MS-DOS computers to have access to memory above 640 KB.


The EMM386 file is an external command in MS-DOS command and is available in the below versions of Windows and MS-DOS as emm386.exe.

EMM386 Syntax

Turns on or off EMM386 expanded memory support.

EMM386 [ON | OFF | AUTO] [W=ON | W=OFF]

ON | OFF | AUTO Activates or suspends EMM386.EXE device driver, or places it in auto mode.
W=ON | OFF Turns on or off Weitek coprocessor support.

EMM386 examples


Typed alone would load the extended memory manager, usually by default this would be loaded in the autoexec.bat.

EMM386 error messages

EMM386 error number Description
0 Divide Error
1 Debugger interrupt
2 Non-maskable interrupt
3 Breakpoint
4 Overflow interrupt
5 Array boundary violation.
6 Invalid Opcode
7 Coprocessor not available.
8 Double fault
9 Coprocessor segment overran.
10 Invalid task statement.
11 Segment not present.
12 Stack exception.
13 General Violation
14 Page fault
16 Coprocessor Error

To resolve error 12 from C:\> type edit config.sys and add "STACKS=16,256" to the file. If you already have a stacks line in the config.sys, ensure it is equal to 16,256.

Error 13 is an indication that program or driver is trying to use protected mode without cooperating with EMM386. You may need to obtain VCPI-compliant version of the program or driver from your vendor to correct this error message.

Additional information