<s>
In	O
DOS	B-General_Concept
memory	I-General_Concept
management	I-General_Concept
,	O
expanded	B-Device
memory	I-Device
is	O
a	O
system	O
of	O
bank	B-General_Concept
switching	I-General_Concept
that	O
provided	O
additional	O
memory	O
to	O
DOS	B-Device
programs	O
beyond	O
the	O
limit	O
of	O
conventional	B-Device
memory	I-Device
(	O
640KiB	O
)	O
.	O
</s>
<s>
Expanded	B-Device
memory	I-Device
is	O
an	O
umbrella	O
term	O
for	O
several	O
incompatible	O
technology	O
variants	O
.	O
</s>
<s>
The	O
most	O
widely	O
used	O
variant	O
was	O
the	O
Expanded	B-Device
Memory	I-Device
Specification	O
(	O
EMS	O
)	O
,	O
which	O
was	O
developed	O
jointly	O
by	O
Lotus	O
Software	O
,	O
Intel	O
,	O
and	O
Microsoft	O
,	O
so	O
that	O
this	O
specification	O
was	O
sometimes	O
referred	O
to	O
as	O
"	O
LIM	O
EMS	O
"	O
.	O
</s>
<s>
The	O
first	O
widely	O
implemented	O
version	O
was	O
EMS	O
3.2	O
,	O
which	O
supported	O
up	O
to	O
8MiB	O
of	O
expanded	B-Device
memory	I-Device
and	O
uses	O
parts	O
of	O
the	O
address	O
space	O
normally	O
dedicated	O
to	O
communication	O
with	O
peripherals	O
(	O
upper	B-Device
memory	I-Device
)	O
to	O
map	O
portions	O
of	O
the	O
expanded	B-Device
memory	I-Device
.	O
</s>
<s>
EEMS	O
ultimately	O
was	O
incorporated	O
in	O
LIM	O
EMS	O
4.0	O
,	O
which	O
supported	O
up	O
to	O
32MiB	O
of	O
expanded	B-Device
memory	I-Device
and	O
provided	O
some	O
support	O
for	O
DOS	B-Device
multitasking	B-Operating_System
as	O
well	O
.	O
</s>
<s>
The	O
use	O
of	O
expanded	B-Device
memory	I-Device
became	O
common	O
with	O
games	O
and	O
business	O
programs	O
such	O
as	O
Lotus	B-Application
1-2-3	I-Application
in	O
the	O
late	O
1980s	O
through	O
the	O
mid-1990s	O
,	O
but	O
its	O
use	O
declined	O
as	O
users	O
switched	O
from	O
DOS	B-Device
to	O
protected-mode	B-Application
operating	O
systems	O
such	O
as	O
Linux	B-Application
,	O
IBM	B-Application
OS/2	I-Application
,	O
and	O
Microsoft	B-Application
Windows	I-Application
.	O
</s>
<s>
The	O
8088	B-Device
processor	O
of	O
the	O
IBM	B-Device
PC	I-Device
and	O
IBM	B-Device
PC/XT	I-Device
could	O
address	O
one	O
megabyte	O
(	O
MiB	O
,	O
or	O
220	O
bytes	O
)	O
of	O
memory	O
.	O
</s>
<s>
It	O
inherited	O
this	O
limit	O
from	O
the	O
20-bit	O
external	O
address	O
bus	O
(	O
and	O
overall	O
memory	O
addressing	O
architecture	O
)	O
of	O
the	O
Intel	B-General_Concept
8086	I-General_Concept
.	O
</s>
<s>
The	O
designers	O
of	O
the	O
PC	O
allocated	O
the	O
lower	O
640KiB	O
(	O
bytes	O
)	O
of	O
address	O
space	O
for	O
read-write	O
program	O
memory	O
(	O
RAM	O
)	O
,	O
called	O
conventional	B-Device
memory	I-Device
,	O
and	O
the	O
remaining	O
384KiB	O
of	O
memory	O
space	O
was	O
reserved	O
for	O
uses	O
such	O
as	O
the	O
system	B-Operating_System
BIOS	I-Operating_System
,	O
video	O
memory	O
,	O
and	O
memory	O
on	O
expansion	O
peripheral	O
boards	O
.	O
</s>
<s>
Even	O
though	O
the	O
IBM	B-Operating_System
PC	I-Operating_System
AT	I-Operating_System
,	O
introduced	O
in	O
1984	O
,	O
used	O
the	O
80286	B-General_Concept
chip	O
that	O
could	O
address	O
up	O
to	O
16MiB	O
of	O
RAM	O
as	O
extended	B-Device
memory	I-Device
,	O
it	O
could	O
only	O
do	O
so	O
in	O
protected	B-Application
mode	I-Application
.	O
</s>
<s>
The	O
scarcity	O
of	O
software	O
compatible	O
with	O
protected	B-Application
mode	I-Application
(	O
no	O
standard	O
DOS	B-Device
applications	O
could	O
run	O
in	O
it	O
)	O
meant	O
that	O
the	O
market	O
was	O
still	O
open	O
for	O
another	O
solution	O
.	O
</s>
<s>
To	O
make	O
more	O
memory	O
accessible	O
,	O
a	O
bank	B-General_Concept
switching	I-General_Concept
scheme	O
was	O
devised	O
,	O
where	O
only	O
selected	O
parts	O
of	O
the	O
additional	O
memory	O
would	O
be	O
accessible	O
at	O
any	O
given	O
time	O
.	O
</s>
<s>
Originally	O
,	O
a	O
single	O
64KiB	O
(	O
216	O
bytes	O
)	O
window	O
of	O
memory	O
,	O
called	O
a	O
page	B-General_Concept
frame	I-General_Concept
,	O
was	O
used	O
;	O
later	O
this	O
was	O
made	O
more	O
flexible	O
.	O
</s>
<s>
Programs	O
had	O
to	O
be	O
written	O
in	O
a	O
specific	O
way	O
to	O
access	O
expanded	B-Device
memory	I-Device
.	O
</s>
<s>
The	O
window	O
between	O
conventional	B-Device
memory	I-Device
and	O
expanded	B-Device
memory	I-Device
could	O
be	O
adjusted	O
to	O
access	O
different	O
locations	O
within	O
the	O
expanded	B-Device
memory	I-Device
.	O
</s>
<s>
A	O
first	O
attempt	O
to	O
use	O
a	O
bank	B-General_Concept
switching	I-General_Concept
technique	O
was	O
made	O
by	O
Tall	O
Tree	O
Systems	O
with	O
their	O
JRAM	O
boards	O
,	O
but	O
these	O
did	O
not	O
catch	O
on	O
.	O
</s>
<s>
The	O
first	O
publicly	O
available	O
version	O
of	O
EMS	O
,	O
version	O
3.0	O
allowed	O
access	O
of	O
up	O
to	O
4MiB	O
of	O
expanded	B-Device
memory	I-Device
.	O
</s>
<s>
The	O
final	O
version	O
of	O
EMS	O
,	O
version	O
4.0	O
increased	O
the	O
maximum	O
amount	O
of	O
expanded	B-Device
memory	I-Device
to	O
32MiB	O
and	O
supported	O
additional	O
functionality	O
.	O
</s>
<s>
Microsoft	O
thought	O
that	O
bank	B-General_Concept
switching	I-General_Concept
was	O
an	O
inelegant	O
and	O
temporary	O
,	O
but	O
necessary	O
stopgap	O
measure	O
.	O
</s>
<s>
Slamming	O
his	O
fist	O
on	O
the	O
table	O
during	O
an	O
interview	O
Bill	O
Gates	O
said	O
of	O
expanded	B-Device
memory	I-Device
,	O
"	O
It	O
's	O
garbage	O
!	O
</s>
<s>
It	O
's	O
a	O
kludge	B-Architecture
!	O
</s>
<s>
EMS	O
3.2	O
used	O
a	O
64KiB	O
region	O
in	O
the	O
upper	O
384KiB	O
(	O
upper	B-Device
memory	I-Device
area	I-Device
)	O
divided	O
into	O
four	O
16KiB	O
pages	B-General_Concept
,	O
which	O
could	O
be	O
used	O
to	O
map	O
portions	O
of	O
the	O
expanded	B-Device
memory	I-Device
.	O
</s>
<s>
EEMS	O
allowed	O
any	O
16KiB	O
region	O
in	O
lower	O
RAM	O
to	O
be	O
mapped	O
to	O
expanded	B-Device
memory	I-Device
,	O
as	O
long	O
as	O
it	O
was	O
not	O
associated	O
with	O
interrupts	B-Application
or	O
dedicated	O
I/O	O
memory	O
such	O
as	O
network	O
or	O
video	O
cards	O
.	O
</s>
<s>
These	O
features	O
were	O
used	O
by	O
early	O
DOS	B-Device
multitasker	O
software	O
such	O
as	O
DESQview	B-Operating_System
.	O
</s>
<s>
This	O
allowed	O
a	O
primitive	O
form	O
of	O
DOS	B-Device
multitasking	B-Operating_System
.	O
</s>
<s>
The	O
Expanded	B-Device
Memory	I-Device
Specification	O
(	O
EMS	O
)	O
is	O
the	O
specification	O
describing	O
the	O
use	O
of	O
expanded	B-Device
memory	I-Device
.	O
</s>
<s>
EMS	O
functions	O
are	O
accessible	O
through	O
software	O
interrupt	B-Application
67h	O
.	O
</s>
<s>
Programs	O
using	O
EMS	O
must	O
first	O
establish	O
the	O
presence	O
of	O
an	O
installed	O
expanded	B-Device
memory	I-Device
manager	O
(	O
EMM	O
)	O
by	O
checking	O
for	O
a	O
device	B-Application
driver	I-Application
with	O
the	O
device	O
name	O
EMMXXXX0	O
.	O
</s>
<s>
IBM	O
developed	O
their	O
own	O
memory	O
standard	O
called	O
Expanded	B-Device
Memory	I-Device
Adapter	I-Device
(	O
XMA	O
)	O
;	O
the	O
IBM	O
DOS	B-Device
driver	O
for	O
it	O
was	O
XMAEM.SYS	O
.	O
</s>
<s>
Unlike	O
EMS	O
,	O
the	O
IBM	O
expansion	O
boards	O
could	O
be	O
addressed	O
both	O
using	O
an	O
expanded	B-Device
memory	I-Device
model	O
and	O
as	O
extended	B-Device
memory	I-Device
.	O
</s>
<s>
The	O
expanded	B-Device
memory	I-Device
hardware	O
interface	O
used	O
by	O
XMA	O
boards	O
is	O
,	O
however	O
,	O
incompatible	O
with	O
EMS	O
,	O
but	O
a	O
XMA2EMS.SYS	O
driver	O
provided	O
EMS	O
emulation	O
for	O
XMA	O
boards	O
.	O
</s>
<s>
XMA	O
boards	O
were	O
first	O
introduced	O
for	O
the	O
1986	O
(	O
revamped	O
)	O
models	O
of	O
the	O
3270	B-Device
PC	I-Device
.	O
</s>
<s>
This	O
insertion	O
of	O
a	O
memory	O
window	O
into	O
the	O
peripheral	O
address	O
space	O
could	O
originally	O
be	O
accomplished	O
only	O
through	O
specific	O
expansion	O
boards	O
,	O
plugged	O
into	O
the	O
ISA	B-Architecture
expansion	O
bus	O
of	O
the	O
computer	O
.	O
</s>
<s>
Famous	O
1980s	O
expanded	B-Device
memory	I-Device
boards	O
were	O
AST	O
RAMpage	O
,	O
IBM	O
PS/2	O
80286	B-General_Concept
Memory	O
Expansion	O
Option	O
,	O
AT&T	O
Expanded	B-Device
Memory	I-Device
Adapter	I-Device
and	O
the	O
Intel	O
Above	O
Board	O
.	O
</s>
<s>
Given	O
the	O
price	O
of	O
RAM	O
during	O
the	O
period	O
,	O
up	O
to	O
several	O
hundred	O
dollars	O
per	O
MiB	O
,	O
and	O
the	O
quality	O
and	O
reputation	O
of	O
the	O
above	O
brand	O
names	O
,	O
an	O
expanded	B-Device
memory	I-Device
board	O
was	O
very	O
expensive	O
.	O
</s>
<s>
Later	O
,	O
some	O
motherboard	B-Device
chipsets	B-Device
of	O
Intel	O
80286-based	O
computers	O
implemented	O
an	O
expanded	B-Device
memory	I-Device
scheme	O
that	O
did	O
not	O
require	O
add-on	O
boards	O
,	O
notably	O
the	O
NEAT	B-Device
chipset	I-Device
.	O
</s>
<s>
Typically	O
,	O
software	O
switches	O
determined	O
how	O
much	O
memory	O
should	O
be	O
used	O
as	O
expanded	B-Device
memory	I-Device
and	O
how	O
much	O
should	O
be	O
used	O
as	O
extended	B-Device
memory	I-Device
.	O
</s>
<s>
An	O
expanded-memory	O
board	O
,	O
being	O
a	O
hardware	O
peripheral	O
,	O
needed	O
a	O
software	O
device	B-Application
driver	I-Application
,	O
which	O
exported	O
its	O
services	O
.	O
</s>
<s>
Such	O
a	O
device	B-Application
driver	I-Application
was	O
called	O
expanded-memory	O
manager	O
.	O
</s>
<s>
Later	O
,	O
the	O
expression	O
became	O
associated	O
with	O
software-only	O
solutions	O
requiring	O
the	O
Intel	B-General_Concept
80386	I-General_Concept
processor	O
,	O
for	O
example	O
Quarterdeck	O
's	O
QEMM	B-Device
,	O
Qualitas	O
 '	O
386MAX	B-Device
or	O
the	O
default	O
EMM386	B-Device
in	O
MS-DOS	O
,	O
PCDOS	O
and	O
DR-DOS	O
.	O
</s>
<s>
Beginning	O
in	O
1986	O
,	O
the	O
built-in	O
memory	O
management	O
features	O
of	O
Intel	B-General_Concept
80386	I-General_Concept
processor	O
freely	O
modeled	O
the	O
address	O
space	O
when	O
running	O
legacy	O
real-mode	O
software	O
,	O
making	O
hardware	O
solutions	O
unnecessary	O
.	O
</s>
<s>
Expanded	B-Device
memory	I-Device
could	O
be	O
simulated	O
in	O
software	O
.	O
</s>
<s>
The	O
first	O
software	O
expanded-memory	O
management	O
(	O
emulation	O
)	O
program	O
was	O
CEMM	B-Device
,	O
available	O
in	O
September	O
1986	O
as	O
a	O
utility	O
for	O
the	O
Compaq	B-Device
Deskpro	I-Device
386	I-Device
.	O
</s>
<s>
A	O
popular	O
and	O
well-featured	O
commercial	O
solution	O
was	O
Quarterdeck	O
's	O
QEMM	B-Device
.	O
</s>
<s>
A	O
contender	O
was	O
Qualitas	O
 '	O
386MAX	B-Device
.	O
</s>
<s>
Functionality	O
was	O
later	O
incorporated	O
into	O
MS-DOS	O
4.01	O
in	O
1989	O
and	O
into	O
DR	O
DOS	B-Device
5.0	O
in	O
1990	O
,	O
as	O
EMM386	B-Device
.	O
</s>
<s>
Notably	O
,	O
they	O
allowed	O
using	O
parts	O
of	O
the	O
upper	B-Device
memory	I-Device
area	I-Device
(	O
UMA	B-Device
)	O
(	O
the	O
upper	O
384KiB	O
of	O
real-mode	O
address	O
space	O
)	O
called	O
upper	B-Device
memory	I-Device
blocks	I-Device
(	O
UMBs	O
)	O
and	O
provided	O
tools	O
for	O
loading	O
small	O
programs	O
,	O
typically	O
terminate-and-stay-resident	O
programs	O
inside	O
(	O
"	O
LOADHI	O
"	O
or	O
"	O
LOADHIGH	O
"	O
)	O
.	O
</s>
<s>
Interaction	O
between	O
extended	B-Device
memory	I-Device
,	O
expanded-memory	O
emulation	O
and	O
DOS	B-Device
extenders	I-Device
ended	O
up	O
being	O
regulated	O
by	O
the	O
XMS	O
,	O
Virtual	O
Control	O
Program	O
Interface	O
(	O
VCPI	O
)	O
,	O
DOS	B-Device
Protected	B-Application
Mode	I-Application
Interface	O
(	O
DPMI	O
)	O
and	O
DOS	B-Device
Protected	B-Application
Mode	I-Application
Services	O
(	O
DPMS	O
)	O
specifications	O
.	O
</s>
<s>
Certain	O
emulation	O
programs	O
,	O
colloquially	O
known	O
as	O
LIMulators	O
,	O
did	O
not	O
rely	O
on	O
motherboard	B-Device
or	O
80386	B-General_Concept
features	O
at	O
all	O
.	O
</s>
<s>
Instead	O
,	O
they	O
reserved	O
64KiB	O
of	O
the	O
base	O
RAM	O
for	O
the	O
expanded	B-Device
memory	I-Device
window	O
,	O
where	O
they	O
copied	O
data	O
to	O
and	O
from	O
either	O
extended	B-Device
memory	I-Device
or	O
the	O
hard	O
disk	O
when	O
application	O
programs	O
requested	O
page	O
switches	O
.	O
</s>
<s>
This	O
technique	O
was	O
offered	O
by	O
AboveDisk	O
from	O
Above	O
Software	O
and	O
by	O
several	O
shareware	B-License
programs	O
.	O
</s>
<s>
It	O
is	O
also	O
possible	O
to	O
emulate	O
EMS	O
by	O
using	O
XMS	B-Device
memory	I-Device
on	O
286	B-General_Concept
CPUs	O
using	O
3rd	O
party	O
utilities	O
like	O
EMM286	O
(	O
.SYS	O
driver	O
)	O
.	O
</s>
<s>
Expanded	B-Device
Memory	I-Device
usage	O
declined	O
in	O
the	O
1990s	O
.	O
</s>
<s>
The	O
IBM	B-Operating_System
AT	I-Operating_System
Intel	B-General_Concept
80286	I-General_Concept
supported	O
24bits	O
of	O
address	O
space	O
(	O
16MiB	O
)	O
in	O
protected	B-Application
mode	I-Application
,	O
and	O
the	O
386	B-General_Concept
supported	O
32-bit	O
addresses	O
,	O
or	O
4gigabytes	O
(	O
232	O
)	O
of	O
RAM	O
–	O
4096	O
times	O
the	O
addressable	O
space	O
of	O
the	O
original	O
8086	B-General_Concept
.	O
</s>
<s>
DOS	B-Device
itself	O
did	O
not	O
directly	O
support	O
protected	B-Application
mode	I-Application
,	O
but	O
Microsoft	O
eventually	O
developed	O
DPMI	O
,	O
and	O
several	O
DOS	B-Device
extenders	I-Device
were	O
published	O
based	O
on	O
it	O
.	O
</s>
<s>
DOS	B-Device
programs	O
like	O
Doom	B-Application
could	O
use	O
extenders	O
like	O
DOS/4G	B-Application
to	O
run	O
in	O
protected	B-Application
mode	I-Application
while	O
still	O
using	O
the	O
DOS	B-Application
API	I-Application
.	O
</s>
<s>
In	O
the	O
early	O
1990s	O
new	O
operating	O
systems	O
like	O
Linux	B-Application
,	O
Windows	O
9x	O
,	O
Windows	B-Device
NT	I-Device
,	O
OS/2	B-Application
,	O
and	O
BSD/OS	B-Operating_System
supported	O
protected	B-Application
mode	I-Application
"	O
out	O
of	O
the	O
box	O
"	O
.	O
</s>
<s>
These	O
and	O
similar	O
developments	O
rendered	O
Expanded	B-Device
Memory	I-Device
an	O
obsolete	O
concept	O
.	O
</s>
