MS DOS Command: EMM386.EXE

Reference from Microsoft MS-DOS cmd help

Description

Enables or disables EMM386 expanded-memory support on a computer with an 80386 or higher processor. The EMM386 command also enables or disables Weitek coprocessor support. Do not use this command when Windows is running.

The EMM386 device driver, EMM386.EXE, provides expanded-memory support and also provides access to the upper memory area. For information about EMM386.EXE, see EMM386.EXE.

Syntax

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

To display the current status of EMM386 expanded-memory support, use the following syntax:

EMM386

Parameters

ON|OFF|AUTO	Activates the EMM386 device driver (if set to ON), or suspends the EMM386 device driver (if set to OFF), or places the EMM386 device driver in auto mode (if set to AUTO). Auto mode enables expanded-memory support only when a program calls for it. The default value is ON.
W=ON|W=OFF	Enables (if set to W=ON) or disables (if set to W=OFF) Weitek coprocessor support. The default value is W=OFF.

Remarks

Installing the EMM386.EXE device driver

To use the EMM386 command, you must have an 80386 or higher processor, and you must also install the EMM386.EXE device driver by using the DEVICE command in your CONFIG.SYS file. If you try to use the EMM386 command on a computer that does not have an 80386 or higher processor, MS-DOS displays the following message:

EMM386 driver not installed

Reactivating EMM386 expanded-memory support

If EMM386 was loaded when MS-DOS started but is not currently in use, the ON parameter reactivates expanded-memory support.

Suspending EMM386 expanded-memory support

If EMM386 expanded-memory support is currently active, handle 0 is the only handle allocated, and EMM386 is not providing access to the upper memory area. The OFF parameter suspends EMM386 expanded-memory support. When EMM386 expanded-memory support is off, the EMM386.EXE device-driver header is changed so that programs cannot use expanded memory. This enables you to run non-VCPI-compliant programs such as Windows 3.0 in Standard mode.

Enabling and disabling Weitek coprocessor support

If the W=ON parameter is specified and the OFF parameter (different from the W=OFF parameter) is not, EMM386 enables Weitek coprocessor support. The high memory area (HMA) must be available to enable Weitek coprocessor support. If you load MS-DOS into the HMA by specifying DOS=HIGH, you may not be able to enable Weitek coprocessor support.

If you specify the W=ON or W=OFF parameter and no Weitek coprocessor is installed in your computer system, MS-DOS displays the following error message:

Weitek Coprocessor not installed