<s>
EMM386	B-Device
is	O
the	O
expanded	B-Device
memory	I-Device
manager	O
of	O
Microsoft	O
's	O
MS-DOS	B-Application
,	O
IBM	O
's	O
PC	B-Operating_System
DOS	I-Operating_System
,	O
Digital	O
Research	O
's	O
DR-DOS	B-Application
,	O
and	O
Datalight	O
's	O
ROM-DOS	B-Operating_System
which	O
is	O
used	O
to	O
create	O
expanded	B-Device
memory	I-Device
using	O
extended	B-Device
memory	I-Device
on	O
Intel	B-General_Concept
80386	I-General_Concept
CPUs	O
.	O
</s>
<s>
There	O
also	O
is	O
an	O
EMM386.EXE	B-Device
available	O
in	O
FreeDOS	B-Application
.	O
</s>
<s>
EMM386.EXE	B-Device
can	O
map	O
memory	O
into	O
unused	O
blocks	O
in	O
the	O
upper	B-Device
memory	I-Device
area	I-Device
(	O
UMA	B-Device
)	O
,	O
allowing	O
device	O
drivers	O
and	O
terminate-and-stay-resident	O
programs	O
to	O
be	O
"	O
loaded	O
high	O
"	O
,	O
preserving	O
conventional	B-Device
memory	I-Device
.	O
</s>
<s>
The	O
technique	O
probably	O
first	O
appeared	O
with	O
the	O
development	O
of	O
CEMM	B-Device
,	O
included	O
with	O
Compaq	O
MS-DOS	B-Application
3.31	O
in	O
1987	O
.	O
</s>
<s>
Microsoft	O
's	O
version	O
first	O
appeared	O
,	O
built-in	O
,	O
with	O
Windows/386	O
2.1	O
in	O
1988	O
and	O
as	O
standalone	O
EMM386.SYS	B-Device
with	O
MS-DOS	B-Application
4.01	O
in	O
1989	O
;	O
the	O
more	O
flexible	O
EMM386.EXE	B-Device
version	O
appeared	O
in	O
MS-DOS	B-Application
5.0	O
in	O
1991	O
.	O
</s>
<s>
Just	O
as	O
the	O
other	O
expanded	B-Device
memory	I-Device
managers	O
,	O
EMM386	B-Device
uses	O
the	O
processor	O
's	O
virtual	B-Application
8086	I-Application
mode	I-Application
.	O
</s>
<s>
This	O
forces	O
memory	O
accesses	O
made	O
by	O
DOS	O
applications	O
to	O
go	O
through	O
the	O
processor	O
's	O
MMU	B-General_Concept
(	O
introduced	O
in	O
the	O
386	B-General_Concept
)	O
,	O
and	O
the	O
page	O
table	O
entries	O
used	O
by	O
the	O
MMU	B-General_Concept
are	O
configured	O
by	O
EMM386	B-Device
to	O
map	O
certain	O
regions	O
in	O
upper	B-Device
memory	I-Device
to	O
areas	O
of	O
extended	B-Device
memory	I-Device
(	O
obtained	O
by	O
EMM386	B-Device
through	O
the	O
extended	B-Device
memory	I-Device
manager	O
HIMEM.SYS	O
)	O
.	O
</s>
<s>
This	O
technique	O
enabled	O
both	O
EMS	O
(	O
expanded	B-Device
memory	I-Device
)	O
as	O
well	O
as	O
UMBs	O
-	O
both	O
of	O
which	O
appear	O
to	O
DOS	O
applications	O
to	O
be	O
memory	O
in	O
the	O
upper	O
area	O
but	O
are	O
in	O
fact	O
mapped	O
to	O
physical	O
memory	O
locations	O
beyond	O
1MB	O
.	O
</s>
<s>
It	O
temporarily	O
shuts	O
down	O
during	O
a	O
Windows	O
session	O
in	O
386	B-General_Concept
Enhanced	O
mode	O
,	O
with	O
Windows	O
 '	O
protected	B-Application
mode	I-Application
kernel	O
taking	O
over	O
its	O
role	O
.	O
</s>
<s>
Windows	O
uses	O
the	O
GEMMIS	O
API	O
to	O
take	O
over	O
memory	O
management	O
from	O
EMM386.EXE	B-Device
.	O
</s>
<s>
Global	O
EMM	O
Import	O
Specification	O
(	O
GEMMIS	O
)	O
is	O
supported	O
via	O
a	O
document	O
available	O
to	O
a	O
select	O
number	O
of	O
memory-manager	O
vendors	O
(	O
"	O
Windows/386	O
Paging	O
Import	O
Specification	O
"	O
)	O
.	O
</s>
<s>
Only	O
a	O
few	O
memory	O
managers	O
implemented	O
the	O
GEMMIS	O
API	O
,	O
some	O
of	O
the	O
ones	O
that	O
include	O
it	O
are	O
:	O
EMM386.EXE	B-Device
,	O
Quarterdeck	B-Device
QEMM	I-Device
,	O
Qualitas	B-Device
386MAX	I-Device
,	O
Helix	B-General_Concept
Netroom	I-General_Concept
and	O
DOSBox	B-Application
builtin	I-Application
DOS	I-Application
.	O
</s>
<s>
Notably	O
missing	O
are	O
FreeDOS	B-Application
's	O
memory	O
managers	O
.	O
</s>
<s>
All	O
of	O
FreeDOS	B-Application
memory	O
managers	O
(	O
HIMEMX.EXE	O
,	O
JEMM386.EXE	O
,	O
JEMMEX.EXE	O
)	O
do	O
not	O
implement	O
the	O
GEMMIS	O
API	O
and	O
Windows	O
fails	O
to	O
start	O
when	O
running	O
in	O
conjunction	O
with	O
JEMMxxx	O
since	O
Windows	O
fails	O
to	O
take	O
over	O
the	O
memory	O
management	O
role	O
.	O
</s>
<s>
Windows	B-Device
ME	I-Device
,	O
Windows	B-Device
98	I-Device
,	O
Windows	B-Application
95	I-Application
,	O
Windows	O
for	O
Workgroups	O
3.1x	O
,	O
and	O
Windows	O
3.xx	O
,	O
all	O
will	O
fail	O
with	O
JEMMxxx	O
displaying	O
:	O
</s>
<s>
Quit	O
the	O
protected-mode	B-Application
software	O
,	O
and	O
then	O
try	O
again	O
.	O
</s>
<s>
using	O
80286	O
Protected	B-Application
Mode	I-Application
,	O
not	O
80386	B-General_Concept
Enhanced	O
Mode	O
.	O
</s>
