<s>
CEMM	B-Device
,	O
for	O
Compaq	O
Expanded	B-Device
Memory	I-Device
Manager	I-General_Concept
was	O
the	O
first	O
so-called	O
PC	O
"	O
memory	B-General_Concept
manager	I-General_Concept
"	O
for	O
Intel	B-General_Concept
80386	I-General_Concept
CPUs	O
,	O
able	O
to	O
provide	O
expanded	B-Device
memory	I-Device
(	O
EMS	O
)	O
emulation	O
by	O
using	O
the	O
virtual	B-Architecture
memory	I-Architecture
features	O
and	O
the	O
virtual	B-Application
8086	I-Application
mode	I-Application
of	O
the	O
CPU	O
.	O
</s>
<s>
It	O
was	O
present	O
in	O
Compaq	O
DOS	O
3.10	O
,	O
shipping	O
with	O
the	O
Compaq	B-Device
Deskpro	I-Device
386	I-Device
in	O
September	O
1986	O
.	O
</s>
<s>
In	O
1986	O
,	O
Compaq	O
was	O
the	O
first	O
vendor	O
to	O
ship	O
a	O
PC	O
compatible	O
computer	O
with	O
a	O
386	B-General_Concept
CPU	O
,	O
the	O
Deskpro	B-Device
386	I-Device
,	O
and	O
it	O
was	O
natural	O
for	O
them	O
to	O
develop	O
solutions	O
leveraging	O
the	O
specific	O
features	O
of	O
their	O
new	O
hardware	O
and	O
in	O
this	O
case	O
allowing	O
existing	O
EMS-compatible	O
DOS	O
programs	O
to	O
access	O
all	O
the	O
memory	O
.	O
</s>
<s>
Although	O
CEMM	B-Device
was	O
called	O
an	O
"	O
expanded	B-Device
memory	I-Device
manager	O
"	O
,	O
it	O
was	O
really	O
a	O
tiny	O
,	O
protected	B-Application
mode	I-Application
,	O
single	O
tasking	O
operating	O
system	O
kernel	O
,	O
also	O
called	O
a	O
virtual	B-Operating_System
machine	I-Operating_System
monitor	I-Operating_System
(	O
VMM	O
)	O
.	O
</s>
<s>
It	O
had	O
to	O
catch	O
all	O
the	O
interrupts	O
and	O
all	O
the	O
exceptions	O
,	O
and	O
to	O
reflect	O
them	O
to	O
the	O
virtual	B-Architecture
machine	I-Architecture
where	O
DOS	O
ran	O
.	O
</s>
<s>
Implementing	O
a	O
VMM	O
was	O
not	O
CEMM	B-Device
's	O
raison	O
d'etre	O
,	O
but	O
EMS	O
emulation	O
required	O
paging	O
,	O
and	O
paging	O
required	O
protected	B-Application
mode	I-Application
.	O
</s>
<s>
The	O
only	O
way	O
to	O
run	O
existing	O
real-mode	B-Application
DOS	O
and	O
BIOS	O
code	O
was	O
therefore	O
through	O
a	O
VMM	O
.	O
</s>
<s>
Because	O
CEMM	B-Device
put	O
the	O
CPU	O
into	O
protected	B-Application
mode	I-Application
,	O
other	O
programs	O
(	O
DOS	B-Device
extenders	I-Device
)	O
could	O
not	O
do	O
this	O
anymore	O
by	O
themselves	O
.	O
</s>
<s>
A	O
special	O
API	O
,	O
the	O
VCPI	O
,	O
had	O
to	O
be	O
developed	O
to	O
allow	O
running	O
DOS	B-Device
extender	I-Device
programs	O
.	O
</s>
<s>
The	O
first	O
CEMM	B-Device
compatible	O
with	O
VCPI	O
was	O
4.0	O
,	O
provided	O
with	O
Compaq	O
DOS	O
4.01	O
.	O
</s>
<s>
However	O
,	O
over	O
time	O
,	O
QEMM	B-Device
and	O
386MAX	B-Device
became	O
the	O
standard	O
packages	O
.	O
</s>
<s>
Windows/386	O
and	O
later	O
releases	O
contained	O
a	O
built-in	O
expanded	B-Device
memory	I-Device
manager	O
(	O
EMM386	B-Device
)	O
available	O
during	O
Windows	O
sessions	O
and	O
otherwise	O
used	O
for	O
running	O
multiple	O
DOS	O
virtual	B-Architecture
machines	I-Architecture
.	O
</s>
<s>
MS-DOS	B-Application
4.01	O
(	O
in	O
1989	O
)	O
and	O
DR-DOS	B-Application
5.0	O
(	O
in	O
1990	O
)	O
popularized	O
the	O
technology	O
outside	O
of	O
the	O
Windows	O
context	O
.	O
</s>
<s>
Microsoft	O
's	O
EMM386	B-Device
implementation	O
was	O
based	O
on	O
CEMM	B-Device
.	O
</s>
