<s>
Remote	B-Device
Initial	I-Device
Program	I-Device
Load	I-Device
(	O
RIPL	O
or	O
RPL	O
)	O
is	O
a	O
protocol	O
for	O
starting	O
a	O
computer	O
and	O
loading	B-Device
its	O
operating	B-General_Concept
system	I-General_Concept
from	O
a	O
server	B-Application
via	O
a	O
network	B-Architecture
.	O
</s>
<s>
Such	O
a	O
server	B-Application
runs	O
a	O
network	B-Protocol
operating	I-Protocol
system	I-Protocol
such	O
as	O
LAN	B-Algorithm
Manager	I-Algorithm
,	O
LAN	B-Operating_System
Server	I-Operating_System
,	O
Windows	B-Device
NT	I-Device
Server	I-Device
,	O
Novell	B-Operating_System
NetWare	I-Operating_System
,	O
LANtastic	B-Operating_System
,	O
Solaris	B-Application
or	O
Linux	B-Application
.	O
</s>
<s>
RIPL	O
is	O
similar	O
to	O
Preboot	B-Device
Execution	I-Device
Environment	I-Device
(	O
PXE	O
)	O
,	O
but	O
it	O
uses	O
the	O
Novell	O
NetWare-based	O
boot	B-Operating_System
method	O
.	O
</s>
<s>
IBM	B-Operating_System
LAN	I-Operating_System
Server	I-Operating_System
enables	O
clients	O
(	O
RIPL	O
requesters	O
)	O
to	O
load	O
the	O
operating	B-General_Concept
systems	I-General_Concept
DOS	B-Device
or	O
OS/2	B-Application
via	O
the	O
802.2/DLC	O
-protocol	O
from	O
the	O
LAN	B-General_Concept
(	O
often	O
Token	B-Device
Ring	I-Device
)	O
.	O
</s>
<s>
Therefore	O
,	O
the	O
server	B-Application
compares	O
the	O
clients	O
 '	O
requests	O
with	O
entries	O
in	O
its	O
RPL.MAP	O
table	O
.	O
</s>
<s>
Remote	O
booting	B-Operating_System
DOS	B-Device
workstations	O
via	O
boot	B-Operating_System
images	I-Operating_System
was	O
supported	O
as	O
early	O
as	O
1990	O
by	O
IBM	B-Operating_System
LAN	I-Operating_System
Server	I-Operating_System
1.2	O
via	O
its	O
PCDOSRPL	O
protocol	O
.	O
</s>
<s>
IBM	B-Operating_System
LAN	I-Operating_System
Server	I-Operating_System
2.0	O
introduced	O
remote	O
booting	B-Operating_System
of	O
OS/2	B-Application
stations	O
(	O
since	O
OS/2	B-Application
1.30.1	O
)	O
in	O
1992	O
.	O
</s>
<s>
For	O
DOS	B-Device
remote	O
boot	B-Operating_System
to	O
work	O
,	O
the	O
RPL	O
boot	B-Operating_System
loader	O
is	O
loaded	O
into	O
the	O
client	O
's	O
memory	O
over	O
the	O
network	B-Architecture
before	O
the	O
operating	B-General_Concept
system	I-General_Concept
starts	O
.	O
</s>
<s>
Without	O
special	O
precautions	O
the	O
operating	B-General_Concept
system	I-General_Concept
could	O
easily	O
overwrite	O
the	O
RPL	O
code	O
during	O
boot	B-Operating_System
,	O
since	O
the	O
RPL	O
code	O
resides	O
in	O
unallocated	O
memory	O
(	O
typically	O
at	O
the	O
top	O
of	O
the	O
available	O
conventional	B-Device
memory	I-Device
)	O
.	O
</s>
<s>
INT	O
12h	O
is	O
used	O
by	O
DOS	B-Device
to	O
query	O
the	O
amount	O
of	O
available	O
memory	O
when	O
initializing	O
its	O
own	O
real-mode	O
memory	O
allocation	O
scheme	O
.	O
</s>
<s>
This	O
causes	O
problems	O
on	O
more	O
modern	O
DOS	B-Device
systems	O
,	O
where	O
free	O
real-mode	O
address	O
ranges	O
may	O
be	O
utilized	O
by	O
the	O
operating	B-General_Concept
system	I-General_Concept
in	O
order	O
to	O
relocate	O
parts	O
of	O
itself	O
and	O
load	O
drivers	O
high	O
,	O
so	O
that	O
the	O
amount	O
of	O
available	O
conventional	B-Device
memory	I-Device
is	O
maximized	O
.	O
</s>
<s>
Typically	O
,	O
various	O
operating	B-General_Concept
system	I-General_Concept
vendor	O
and	O
version	O
specific	O
"	O
dirty	O
tricks	O
"	O
had	O
to	O
be	O
used	O
by	O
the	O
RPL	O
code	O
in	O
order	O
to	O
survive	O
this	O
very	O
dynamic	O
boot	B-Operating_System
process	I-Operating_System
and	O
let	O
DOS	B-Device
regain	O
control	O
over	O
the	O
memory	O
occupied	O
by	O
RPL	O
once	O
the	O
boot	B-Operating_System
is	O
complete	O
in	O
a	O
seamless	O
manner	O
.	O
</s>
<s>
Since	O
MS-DOS/PC	O
DOS	B-Device
5.0	O
and	O
DR	O
DOS	B-Device
6.0	O
,	O
the	O
operating	B-General_Concept
system	I-General_Concept
checks	O
if	O
the	O
RPL	O
has	O
hooked	O
INT	O
2Fh	O
by	O
looking	O
for	O
a	O
"	O
RPL	O
"	O
signature	O
at	O
the	O
code	O
pointed	O
to	O
by	O
INT2Fh	O
.	O
</s>
<s>
If	O
present	O
,	O
DOS	B-Device
calls	O
INT2Fh/AX	O
=	O
4A06h	O
to	O
retrieve	O
the	O
amount	O
of	O
memory	O
from	O
the	O
RPL	O
and	O
integrate	O
it	O
into	O
its	O
own	O
memory	O
allocation	O
,	O
thereby	O
protecting	O
the	O
RPL	O
code	O
from	O
being	O
overwritten	O
by	O
other	O
programs	O
.	O
</s>
<s>
Still	O
,	O
it	O
remained	O
the	O
RPL	O
's	O
difficult	O
responsibility	O
to	O
cleanly	O
remove	O
itself	O
from	O
memory	O
at	O
the	O
end	O
of	O
the	O
boot	B-Operating_System
phase	O
,	O
if	O
possible	O
.	O
</s>
<s>
If	O
DRDOS	O
detects	O
the	O
presence	O
of	O
RPLOADER	O
rather	O
than	O
RPL	O
only	O
,	O
it	O
starts	O
to	O
issue	O
INT2F/AX	O
=	O
12FFh/BX	O
=	O
0005h	O
broadcasts	O
at	O
certain	O
critical	O
stages	O
in	O
the	O
boot	B-Operating_System
process	I-Operating_System
.	O
</s>
<s>
The	O
RPL	O
code	O
can	O
use	O
them	O
to	O
relocate	O
itself	O
in	O
memory	O
(	O
in	O
order	O
to	O
avoid	O
conflicts	O
with	O
other	O
resident	O
software	O
or	O
to	O
avoid	O
memory	B-Architecture
fragmentation	I-Architecture
when	O
the	O
RPL	O
memory	O
is	O
freed	O
later	O
on	O
)	O
,	O
or	O
to	O
hook	O
into	O
and	O
better	O
integrate	O
with	O
the	O
operating	B-General_Concept
system	I-General_Concept
in	O
order	O
to	O
perform	O
its	O
final	O
cleanup	O
tasks	O
in	O
a	O
well-defined	O
and	O
coordinated	O
manner	O
through	O
a	O
robust	O
and	O
supported	O
backend	B-Architecture
interface	I-Architecture
rather	O
than	O
mere	O
hacks	O
.	O
</s>
<s>
This	O
helps	O
to	O
improve	O
compatibility	O
without	O
having	O
to	O
adapt	O
the	O
RPL	O
code	O
with	O
each	O
new	O
version	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
,	O
and	O
it	O
avoids	O
unnecessary	O
memory	B-Architecture
fragmentation	I-Architecture
and	O
thereby	O
increases	O
available	O
memory	O
for	O
DOS	B-Device
programs	O
to	O
run	O
.	O
</s>
<s>
The	O
interface	O
can	O
also	O
be	O
utilized	O
to	O
run	O
DRDOS	O
as	O
a	O
task	O
under	O
a	O
host	O
operating	B-General_Concept
system	I-General_Concept
such	O
as	O
Concurrent	B-Operating_System
DOS	I-Operating_System
.	O
</s>
