<s>
A	O
monolithic	B-Operating_System
kernel	I-Operating_System
is	O
an	O
operating	O
system	O
architecture	O
where	O
the	O
entire	O
operating	O
system	O
is	O
working	O
in	O
kernel	B-Operating_System
space	I-Operating_System
.	O
</s>
<s>
The	O
monolithic	O
model	O
differs	O
from	O
other	O
operating	O
system	O
architectures	O
(	O
such	O
as	O
the	O
microkernel	B-Operating_System
architecture	O
)	O
in	O
that	O
it	O
alone	O
defines	O
a	O
high-level	O
virtual	O
interface	O
over	O
computer	O
hardware	O
.	O
</s>
<s>
A	O
set	O
of	O
primitives	O
or	O
system	B-Operating_System
calls	I-Operating_System
implement	O
all	O
operating	O
system	O
services	O
such	O
as	O
process	B-Operating_System
management	O
,	O
concurrency	B-Operating_System
,	O
and	O
memory	B-General_Concept
management	I-General_Concept
.	O
</s>
<s>
Device	O
drivers	O
can	O
be	O
added	O
to	O
the	O
kernel	B-Operating_System
as	O
modules	B-Architecture
.	O
</s>
<s>
Modular	B-Architecture
operating	O
systems	O
such	O
as	O
OS-9	B-Operating_System
and	O
most	O
modern	O
monolithic	O
operating	O
systems	O
such	O
as	O
OpenVMS	B-Operating_System
,	O
Linux	B-Operating_System
,	O
BSD	B-Operating_System
,	O
SunOS	B-Operating_System
,	O
AIX	B-Application
,	O
and	O
MULTICS	B-Application
can	O
dynamically	O
load	O
(	O
and	O
unload	O
)	O
executable	O
modules	B-Architecture
at	O
runtime	O
.	O
</s>
<s>
This	O
modularity	B-Architecture
of	O
the	O
operating	O
system	O
is	O
at	O
the	O
binary	O
(	O
image	O
)	O
level	O
and	O
not	O
at	O
the	O
architecture	O
level	O
.	O
</s>
<s>
Modular	B-Architecture
monolithic	O
operating	O
systems	O
are	O
not	O
to	O
be	O
confused	O
with	O
the	O
architectural	O
level	O
of	O
modularity	B-Architecture
inherent	O
in	O
server-client	B-Operating_System
operating	O
systems	O
(	O
and	O
its	O
derivatives	O
sometimes	O
marketed	O
as	O
hybrid	B-Operating_System
kernel	I-Operating_System
)	O
which	O
use	O
microkernels	B-Operating_System
and	O
servers	O
(	O
not	O
to	O
be	O
mistaken	O
for	O
modules	B-Architecture
or	O
daemons	O
)	O
.	O
</s>
<s>
Practically	O
speaking	O
,	O
dynamically	O
loading	O
modules	B-Architecture
is	O
simply	O
a	O
more	O
flexible	O
way	O
of	O
handling	O
the	O
operating	O
system	O
image	O
at	O
runtime	O
—	O
as	O
opposed	O
to	O
rebooting	O
with	O
a	O
different	O
operating	O
system	O
image	O
.	O
</s>
<s>
The	O
modules	B-Architecture
allow	O
easy	O
extension	O
of	O
the	O
operating	O
systems	O
 '	O
capabilities	O
as	O
required	O
.	O
</s>
<s>
Dynamically	O
loadable	O
modules	B-Architecture
incur	O
a	O
small	O
overhead	O
when	O
compared	O
to	O
building	O
the	O
module	B-Architecture
into	O
the	O
operating	O
system	O
image	O
.	O
</s>
<s>
However	O
,	O
in	O
some	O
cases	O
,	O
loading	O
modules	B-Architecture
dynamically	O
(	O
as-needed	O
)	O
helps	O
to	O
keep	O
the	O
amount	O
of	O
code	O
running	O
in	O
kernel	B-Operating_System
space	I-Operating_System
to	O
a	O
minimum	O
;	O
for	O
example	O
,	O
to	O
minimize	O
operating	O
system	O
footprint	O
for	O
embedded	O
devices	O
or	O
those	O
with	O
limited	O
hardware	O
resources	O
.	O
</s>
<s>
Namely	O
,	O
an	O
unloaded	O
module	B-Architecture
need	O
not	O
be	O
stored	O
in	O
scarce	O
random	B-Architecture
access	I-Architecture
memory	I-Architecture
.	O
</s>
