<s>
A	O
NetWare	B-Application
Loadable	I-Application
Module	I-Application
(	O
NLM	B-Application
)	O
is	O
a	O
loadable	B-Application
kernel	I-Application
module	I-Application
(	O
a	O
binary	O
code	O
module	B-Application
)	O
that	O
can	O
be	O
loaded	O
into	O
Novell	B-Operating_System
's	I-Operating_System
NetWare	I-Operating_System
operating	O
system	O
.	O
</s>
<s>
NLMs	B-Application
can	O
implement	O
hardware	O
drivers	O
,	O
server	O
functions	O
(	O
e.g.	O
</s>
<s>
GroupWise	B-Operating_System
)	O
,	O
system	O
libraries	O
or	O
utilities	O
.	O
</s>
<s>
NLMs	B-Application
were	O
supported	O
beginning	O
with	O
the	O
Intel	O
80386-based	O
NetWare	B-Operating_System
version	O
3.x	O
.	O
</s>
<s>
Prior	O
versions	O
of	O
NetWare	B-Operating_System
had	O
a	O
monolithic	O
kernel	B-Operating_System
,	O
and	O
significant	O
hardware	O
or	O
functionality	O
changes	O
required	O
re-linking	O
the	O
kernel	B-Operating_System
from	O
object	O
modules	B-Application
.	O
</s>
<s>
Due	O
to	O
stability	O
issues	O
with	O
early	O
third-party	O
NLMs	B-Application
,	O
they	O
never	O
became	O
popular	O
for	O
server	O
application	O
programming	O
,	O
with	O
few	O
exceptions	O
like	O
antivirus	B-Application
programs	I-Application
,	O
backup	B-Protocol
programs	O
and	O
certain	O
database	O
products	O
.	O
</s>
<s>
Upon	O
loading	O
,	O
a	O
NLM	B-Application
requests	O
resources	O
,	O
such	O
as	O
memory	O
and	O
process	O
threads	O
,	O
from	O
the	O
NetWare	B-Operating_System
kernel	I-Operating_System
.	O
</s>
<s>
The	O
NetWare	B-Operating_System
kernel	I-Operating_System
tracks	O
such	O
requests	O
,	O
and	O
can	O
identify	O
memory	O
and	O
other	O
resources	O
assigned	O
to	O
a	O
specific	O
NLM	B-Application
.	O
</s>
<s>
NLMs	B-Application
may	O
auto-load	O
other	O
NLMs	B-Application
upon	O
which	O
they	O
themselves	O
depend	O
.	O
</s>
<s>
NLMs	B-Application
may	O
register	O
commands	O
with	O
the	O
NetWare	B-Operating_System
kernel	I-Operating_System
,	O
extending	O
the	O
command	O
vocabulary	O
available	O
at	O
the	O
NetWare	B-Operating_System
console	O
prompt	O
.	O
</s>
<s>
When	O
properly	O
coded	O
,	O
NLMs	B-Application
can	O
be	O
re-entrant	O
,	O
allowing	O
multiple	O
instances	O
of	O
the	O
same	O
code	O
to	O
be	O
loaded	O
and	O
run	O
.	O
</s>
<s>
Initially	O
,	O
Novell	O
published	O
a	O
development	O
toolkit	O
for	O
NLM	B-Application
programming	O
including	O
kernel	B-Operating_System
API	O
documentation	O
and	O
a	O
C	B-Language
compiler	I-Language
(	O
Watcom	O
)	O
,	O
but	O
third-party	O
support	O
for	O
the	O
NLM	B-Application
executable	B-Application
function	O
was	O
very	O
limited	O
.	O
</s>
<s>
In	O
early	O
NetWare	B-Operating_System
versions	O
(	O
prior	O
to	O
v4.x	O
)	O
,	O
all	O
processes	O
were	O
executed	O
in	O
the	O
kernel	B-Operating_System
address	O
space	O
,	O
without	O
specific	O
memory	O
protection	O
.	O
</s>
<s>
It	O
was	O
therefore	O
possible	O
for	O
bugs	B-Error_Name
in	O
NLMs	B-Application
to	O
overwrite	O
the	O
kernel	B-Operating_System
's	O
or	O
other	O
NLM	B-Application
's	O
address	O
space	O
and	O
ultimately	O
crash	O
the	O
server	O
in	O
the	O
mainframe-derived	O
Novell	O
terminology	O
,	O
this	O
was	O
known	O
as	O
an	O
ABEND	B-Application
or	O
ABnormal	B-Application
END	I-Application
.	O
</s>
<s>
Moreover	O
,	O
NetWare	B-Operating_System
used	O
a	O
non-preemptive	O
,	O
or	O
cooperative	B-Operating_System
,	O
multitasking	O
model	O
,	O
meaning	O
that	O
an	O
NLM	B-Application
was	O
required	O
to	O
yield	O
to	O
the	O
kernel	B-Operating_System
regularly	O
.	O
</s>
<s>
An	O
NLM	B-Application
executing	O
an	O
infinite	B-Algorithm
loop	I-Algorithm
,	O
for	O
example	O
,	O
could	O
therefore	O
not	O
be	O
stopped	O
.	O
</s>
<s>
In	O
NetWare	B-Operating_System
v4.x	O
,	O
Novell	O
introduced	O
a	O
limited	O
form	O
of	O
memory	O
protection	O
,	O
which	O
was	O
extended	O
to	O
Protected	O
Address	O
Spaces	O
in	O
NetWare	B-Operating_System
v5.x	O
.	O
</s>
<s>
Through	O
these	O
mechanisms	O
,	O
properly-coded	O
NLMs	B-Application
can	O
be	O
loaded	O
into	O
their	O
own	O
address	O
space	O
,	O
and	O
mis-behaving	O
NLMs	B-Application
can	O
be	O
prevented	O
from	O
compromising	O
the	O
kernel	B-Operating_System
integrity	O
.	O
</s>
<s>
Official	O
compilers	O
that	O
produce	O
NLMs	B-Application
are	O
:	O
</s>
<s>
NLM	B-Application
development	O
is	O
also	O
possible	O
with	O
GNU	O
cc	O
and	O
binutils	O
.	O
</s>
<s>
More	O
details	O
are	O
available	O
in	O
NetWare	B-Application
Loadable	I-Application
Module	I-Application
Programming	O
HOWTO	O
by	O
Martin	O
Hinner	O
.	O
</s>
<s>
Announcing	O
it	O
in	O
March	O
1995	O
,	O
Novell	O
introduced	O
a	O
new	O
32-bit	O
DOS/Windows	O
NetWare	B-Operating_System
client	O
(	O
Client	O
32	O
based	O
on	O
ODI32/NIOS	O
)	O
in	O
1996	O
,	O
replacing	O
the	O
former	O
16-bit	O
client	O
based	O
on	O
ODI/VLM	O
.	O
</s>
<s>
Its	O
NIOS	O
component	O
(	O
NetWare	B-Operating_System
I/O	O
Subsystem	O
)	O
used	O
techniques	O
similar	O
to	O
DPMS	O
to	O
relocate	O
and	O
run	O
NLMs	B-Application
in	O
protected	B-Application
mode	I-Application
and	O
extended	B-Device
memory	I-Device
in	O
order	O
to	O
reduce	O
the	O
conventional	B-Device
memory	I-Device
footprint	O
of	O
the	O
client	O
down	O
to	O
2	O
to	O
5KB	O
.	O
</s>
