The description below is from the book DOS the Easy Way by Everett Murdock Ph.D.
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Type: External (5.0 and later)
EMM386 [on|off|auto] [w=on|off]
Enables or disables EMM386 expanded-memory support on a computer with an
or higher processor. Do not use this command when Windows is running.
The EMM386 device driver, EMM386.EXE, provides expanded-memory support as
as access to the upper memory area. In order to use the EMM386 command
have an 80386 or higher processor and you must install the EMM386.EXE
driver by using the DEVICE command in your CONFIG.SYS file, otherwise the
following message will be displayed:
EMM386 driver not installed
on|off|auto - ON activates the EMM386 device driver, OFF suspends the device
driver, and AUTO places the device driver into auto mode. Auto mode
expanded-memory support only when a program calls for it. The default
w=on|w=off - ON enables Weitek coprocessor support. OFF disables Weitek
coprocessor support. The default is w=off.
If you want to display the current status of EMM386 expanded-memory