Command: jemm386
JEMM386 is an Expanded Memory Manager.
JEMM386 has to be loaded in CONFIG.SYS / FDCONFIG.SYS.
Like other EMMs it installs the following services:
- Uses extended memory to simulate expanded memory (EMS) according to
EMS v3.2 and EMS v4.0.
- Upper memory blocks (UMB) where drivers and resident programs may
be loaded, thus increasing available free DOS memory.
- Mapping RAM to the video address segments A000-AFFF and B000-B7FF.
- VCPI services to allow DOS applications running in V86-mode to
switch to protected mode. VCPI also implements a simple memory
management.
- VDS API to give drivers/applications some control over DMA and
physical addresses in V86-mode.
Syntax:
DEVICE=[drive][path][jemm386.exe] [options]
drive The drive letter, e.g. C:
path The directory, e.g. \example\
or run it from the command line:
[drive][path][jemm386.exe] [options]
Options:
+A20/NOA20 A20-disable emulation on/off (default on).
ALTBOOT Use alternate reboot strategy.
B=segm Specify lowest segment address for EMS banking
(default=4000).
D=n Set DMA buffer size in KB (default=64, max is 128).
EMX Increased EMX DOS extender compatibility.
FASTBOOT Fast reboot. Requires Jemm386 to be loaded in CONFIG.SYS.
FRAME=E000 Set EMS page frame (FRAME=NONE disables frame). Any value
between 8000 and E000 is accepted, but not all will work.
I=start-end Force a region to be used for UMBs. Without this option
range C000-EFFF is scanned for unused pages. May also
be used to add (parts of) regions A000-BFFF or F000-F7FF
as UMBs. Don't use this option if you don't know what
you are doing!
I=TEST Scan ROMs for unused pages, include found regions
as UMBs.
[MAX=]=n Limit for VCPI (and EMS if < 32 MB) memory in KB
(default 120 MB).
MIN=n Reserve up to n KB for EMS/VCPI memory on init
(default=0).
NOCHECK Disallow access to address space without RAM (MMIO)
NOEMS Disable EMS handling.
NODYN No dynamic XMS memory allocation (use MIN= to set fix
amount).
NOHI Don't move resident part into first UMB.
NOINVLPG Don't use INVLPG opcode.
+PGE/NOPGE Page Global Enable feature usage on/off (default off).
RAM/NORAM Try to supply UMBs on/off (default on).
S=start-end Assume Shadow-RAM activated by UMBPCI, include it as UMB.
SB SoundBlaster driver compatibility mode.
SPLIT Regain partially used EPROM 4 KB pages for UMBs.
+VCPI/NOVCPI VCPI Support on/off (default on).
VDS/NOVDS Virtual DMA Services on/off (default on).
+VME/NOVME V86-Mode Extensions on/off (default off).
VERBOSE Display additional details during start (abbr: /V).
X=start-end Exclude region from being touched or used by Jemm386.
X=TEST Scan memory region C000-EFFF for UMB exclusion.
/? Shows the help.
'+': option can be set dynamically by running Jemm386 from the command
line.
When invoked from the command line Jemm386 additionally will understand:
LOAD install
UNLOAD uninstall
Comments:
JEMM386 requires a 80386+ CPU. HIMEMX should be loaded before.
Load JEMM386 as DEVICE=JEMM386.EXE in CONFIG.SYS / FDCONFIG.SYS
(although it is an ".exe"-file!).
For more informations see:
https://github.com/Baron-von-Riedesel/Jemm/tree/master/Html
OR:
https://gitlab.com/FreeDOS/base/jemm/-/tree/master/DOC/JEMM
OR:
C:\FREEDOS\DOC\JEMM\readme.txt (can be installed with FD live CD).
Examples:
IN CONFIG.SYS / FDCONFIG.SYS:
files=20
buffers=30
lastdrive=Z
break=off
DOS=high,umb
device=C:\FREEDOS\BIN\himemx.exe
device=C:\FREEDOS\BIN\jemm386.exe NOEMS
shellhigh=C:\FREEDOS\BIN\command.com C:\FREEDOS\BIN /E:1024
/p:C:\fdauto.bat
See also:
config.sys/fdconfig.sys
devload
(fdxms)
(fdxms286)
himemx
jemmex
xmgr
Copyright © 2011 W. Spiegl, updated 2022.
This file is derived from the FreeDOS Spec Command HOWTO.
See the file H2Cpying for copying conditions.