MS DOS Command: EMM386.EXE

Reference from Microsoft MS-DOS cmd help

Description

Provides access to the upper memory area and uses extended memory to simulate expanded memory. This device driver must be loaded by a DEVICE command in your CONFIG.SYS file and can be used only on computers with an 80386 or higher processor.

EMM386 uses extended memory to simulate expanded memory for programs that can use expanded memory. EMM386 also makes it possible to load programs and device drivers into upper memory blocks (UMBs).

Syntax

DEVICE=[drive:][path]EMM386.EXE [ON|OFF|AUTO] [memory] [MIN=size] [W=ON|W=OFF] [Mx|FRAME=address|/Pmmmm] [Pn=address] [X=mmmm-nnnn] [I=mmmm-nnnn] [B=address] [L=minXMS] [A=altregs] [H=handles] [D=nnn] [RAM=mmmm-nnnn] [NOEMS] [NOVCPI] [HIGHSCAN] [VERBOSE] [WIN=mmmm-nnnn] [NOHI] [ROM=mmmm-nnnn] [NOMOVEXBDA] [ALTBOOT]

Parameters

[drive:][path]	Specifies the location of the EMM386.EXE file.
[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 and upper memory block support only when a program calls for it. The default value is ON. Use the EMM386 command to change this value after EMM386 has started.
memory	Specifies the maximum amount of extended memory (in kilobytes) that you want EMM386 to provide as expanded/Virtual Control Program Interface (EMS/VCPI) memory. This amount is in addition to the memory used for UMBs and EMM386 itself. Values for memory are in the range 64 through the lesser of either 32768 or the amount of extended memory available when EMM386 is loaded. The default value is the amount of free extended memory. If you specify the NOEMS switch, the default value is 0. EMM386 rounds the value down to the nearest multiple of 16.

Switches

MIN=size	Specifies the minimum amount of EMS/VCPI memory (in kilobytes) that EMM386 will provide, if that amount of memory is available. EMM386 reserves this amount of extended memory for use as EMS/VCPI memory when EMM386 is loaded by the DEVICE=EMM386.EXE command in your CONFIG.SYS file. EMM386 may be able to provide additional EMS/VCPI memory (up to the amount specified by the MEMORY parameter) if sufficient XMS memory is available when a program requests EMS/VCPI memory. Values are in the range 0 through the value specified by the MEMORY parameter. The default value is 256. If you specify the NOEMS switch, the default value is 0. If the value of MIN is greater than the value of MEMORY, EMM386 uses the value specified by MIN.
W=ON|W=OFF	Enables or disables support for the Weitek coprocessor. The default setting is W=OFF.
Mx	Specifies the address of the page frame. Valid values for x are in the range 1 through 14. The following list shows each value and its associated base address in hexadecimal format: 1 => C000h 8 => DC00h 2 => C400h 9 => E000h 3 => C800h 10 => 8000h 4 => CC00h 11 => 8400h 5 => D000h 12 => 8800h 6 => D400h 13 => 8C00h 7 => D800h 14 => 9000h Values in the range 10 through 14 should be used only on computers that have 512K of memory.
FRAME=address	Specifies the page-frame segment base directly. To specify a specific segment-base address for the page frame, use the FRAME switch and specify the address you want. Valid values for address are in the ranges 8000h through 9000h and C000h through E000h, in increments of 400h. To provide expanded memory and disable the page frame, you can specify FRAME=NONE; however, this may cause some programs that require expanded memory to work improperly.
/Pmmmm	Specifies the address of the page frame. Valid values for mmmm are in the ranges 8000h through 9000h and C000h through E000h, in increments of 400h.
Pn=address	Specifies the segment address of a specific page, where n is the number of the page you are specifying and address is the segment address you want. Valid values for n are in the range 0 through 255. Valid values for address are in the ranges 8000h through 9C00h and C000h through EC00h, in increments of 400h. The addresses for pages 0 through 3 must be contiguous in order to maintain compatibility with version 3.2 of the Lotus/Intel/Microsoft Expanded Memory Specification (LIM EMS). If you use the Mx switch, the FRAME switch, or the /Pmmmm switch, you cannot specify the addresses for pages 0 through 3 for the /Pmmmm switch.
X=mmmm-nnnn	Prevents EMM386 from using a particular range of segment addresses for an EMS page or for UMBs. Valid values for mmmm and nnnn are in the range A000h through FFFFh and are rounded down to the nearest 4-kilobyte boundary. The X switch takes precedence over the I switch if the two ranges overlap.
I=mmmm-nnnn	Specifies a range of segment addresses to be used (included) for an EMS page or for UMBs. Valid values for mmmm and nnnn are in the range A000h through FFFFh and are rounded down to the nearest 4-kilobyte boundary. The X switch takes precedence over the I switch if the two ranges overlap.
B=address	Specifies the lowest segment address available for EMS "banking" (swapping of 16-kilobyte pages). Valid values are in the range 1000h through 4000h. The default value is 4000h.
l=minXMS	Ensures that the specified amount (in kilobytes) of extended memory will still be available after EMM386 is loaded. The default value is 0.
A=altregs	Specifies how many fast alternate register sets (used for multitasking) you want to allocate to EMM386. Valid values are in the range 0 through 254. The default value is 7. Every alternate register set adds about 200 bytes to the size in memory of EMM386.
H=handles	Specifies how many handles EMM386 can use. Valid values are in the range 2 through 255. The default value is 64.
D=nnn	Specifies how many kilobytes of memory should be reserved for buffered direct memory access (DMA). Discounting floppy-disk DMA, this value should reflect the largest DMA transfer that will occur while EMM386 is active. Valid values for nnn are in the range 16 through 256. The default value is 32.
RAM=mmmm-nnnn	Specifies a range of segment addresses to be used for UMBs and also enables EMS support. If you do not specify a range, EMM386 uses all available adapter space to create UMBs and a page frame for EMS.
NOEMS	Provides access to the upper memory area but prevents access to expanded memory.
NOVCPI	Disables support for VCPI applications. This switch must be used with the NOEMS switch. If you specify the NOVCPI switch without specifying the NOEMS switch, EMM386 does not disable VCPI support. If you specify both switches, EMM386 disregards the MEMORY parameter and the MIN switch. Disabling support for VCPI applications reduces the amount of extended memory allocated.
HIGHSCAN	Specifies that EMM386 use an additional check to determine the availablity of upper memory for use as UMBs or EMS windows. On some computers, specifying this switch may have no effect or cause EMM386 to identify upper memory areas as available when they are not. As a result, your computer might stop responding.
VERBOSE	Directs EMM386 to display status and error messages while loading. By default, EMM386 displays messages only if it encounters an error condition. You can abbreviate VERBOSE as V. (To display status messages without adding the VERBOSE switch, press and hold the ALT key while EMM386 starts and loads.)
WIN=mmmm-nnnn	Reserves a specified range of segment addresses for Windows instead of for EMM386. Valid values for mmmm and nnnn are in the range A000h through FFFFh and are rounded down to the nearest 4-kilobyte boundary. The X switch takes precedence over the WIN switch if the two ranges overlap. The WIN switch takes precedence over the RAM, ROM, and I switches if their ranges overlap.
[NOHI]	Prevents EMM386 from loading into the upper memory area. Normally, a portion of EMM386 is loaded into upper memory. Specifying this switch decreases available conventional memory and increases the upper memory area available for UMBs.
[ROM=mmmm-nnnn]	Specifies a range of segment addresses that EMM386 uses for shadow RAM--random-access memory used for read-only memory (ROM). Valid values for mmmm and nnnn are in the range A000h through FFFFh and are rounded down to the nearest 4-kilobyte boundary. Specifying this switch may speed up your system if it does not already have shadow RAM.
[NOMOVEXBDA]	Prevents EMM386 from moving the extended BIOS data from conventional memory to upper memory.
[ALTBOOT]	Specifies that EMM386 use an alternate handler to restart your computer when you press CTRL+ALT+DEL. Use this switch only if your computer stops responding or exhibits other unusual behavior when EMM386 is loaded and you press CTRL+ALT+DEL.

Remarks

Sharing XMS and EMS memory

EMM386 provides EMS/VCPI memory for programs that require it by converting XMS memory to EMS/VCPI memory. When it is loaded, EMM386 reserves the amount of memory specified by the MIN switch for use as EMS/VCPI memory (the default value is 256K). Once this amount of XMS memory is reserved, it is always available as EMS/VCPI memory and no longer available as XMS memory. EMM386 may be able to convert additional amounts of XMS memory to EMS/VCPI memory, up to the amount specified by the MEMORY parameter. EMM386 returns the additional amount back to XMS memory when it is no longer needed as EMS/VCPI memory.

If you specify MIN=0, EMM386 does not reserve any XMS memory for use as EMS/VCPI memory. Instead, it converts XMS memory to EMS/VCPI memory only when a program requests it. This frees XMS memory when EMS/VCPI memory is not needed. However, EMM386 will not be able to supply the requested amount of EMS/VCPI memory if programs have allocated all the XMS memory at the time of the request.

Must install HIMEM.SYS before EMM386.EXE

You must include a DEVICE command for the HIMEM.SYS device driver in your CONFIG.SYS file before the DEVICE command for EMM386.EXE.

Using EMM386 memory switches

Unless you want to use EMM386 to provide access to the upper memory area, you need not specify memory switches on the DEVICE command line. EMM386 usually runs properly with the default values. In some cases, however, you might want to control how EMM386 uses memory. For example, you can control where EMM386 puts the EMS page frame or which segments it uses for EMS pages. You can use as many of these memory switches as you want, in any order you want.

CAUTION: Use EMM386.EXE parameters carefully. You can make your computer inoperable if you use them incorrectly.

Using EMM386 to provide access to the upper memory area

In addition to providing access to expanded memory, EMM386 provides access to the upper memory area, which you can use to load certain programs and device drivers. You must use either the RAM or NOEMS switch to provide access to the upper memory area.

To give MS-DOS access to the upper memory area but not to expanded memory, use the NOEMS switch. To give MS-DOS access to both the upper memory area and expanded memory, use the RAM switch. The RAM switch provides access to less of the upper memory area for running device drivers and programs than does the NOEMS switch. In either case, you must include the DOS=UMB command in your CONFIG.SYS file. The device command for EMM386.EXE must precede any DEVICEHIGH commands.

Using EMM386 with Windows 3.1

When EMM386 is used with Windows 3.1, the I, X, NOEMS, Mx, Pnnnn, and FRAME switches have precedence over the EMMINCLUDE, EMMEXCLUDE, and EMMPAGEFRAME settings in the Windows SYSTEM.INI file. Changes to these settings in the SYSTEM.INI file have no effect when EMM386 is loaded.

SMARTDRV double buffering may be required to use EMM386

If you have a small computer system interface (SCSI) or enhanced system device interface (ESDI) hard disk or other device, you may have to add the following line to your CONFIG.SYS file:

device=smartdrv.exe /double_buffer

Add the line before any DEVICEHIGH statements and before any statements that load installable device drivers that use expanded memory. The statement enables an SCSI or EDSI controller to transfer information to programs that use the upper memory area or expanded memory.

Examples

To start EMM386 as an expanded-memory emulator, using the default values, add the following lines to your CONFIG.SYS file:

device=himem.sys

device=emm386.exe

Since no location is specified, MS-DOS searches for the EMM386.EXE file in the root directory of your startup drive.

To specify that EMM386 allocate a maximum of 4096K of memory and a guaranteed 256K of memory (the default value), and to specify that the EMM386.EXE file is located in the DOS directory on drive C, add the following line to your CONFIG.SYS file:

device=c:\dos\emm386.exe 4096

To emulate expanded memory, specify the segment-base address D000h for the EMS page frame, and allocate 512K of memory to EMM386, use one of the following commands:

device=emm386.exe 512 frame=d000

device=emm386.exe 512 p0=d000 p1=d400 p2=d800 p3=dc00

Suppose that, in addition to specifying the conditions set in the preceding commands, you want to prevent EMM386 from using the segment addresses E000h through EC00h. To do this and to specify that EMM386 can use 127 handles, add the following line to your CONFIG.SYS file:

device=emm386.exe 512 frame=d000 x=e000-ec00 h=127

To provide access to the upper memory area but not provide EMS/VCPI memory, add the following line to your CONFIG.SYS file:

device=emm386.exe noems novcpi

To provide access to the upper memory area and provide EMS/VCPI memory, add the following line to your CONFIG.SYS file:

device=emm386.exe ram