<s>
PL/S	B-Language
,	O
short	O
for	O
Programming	O
Language/Systems	O
,	O
is	O
a	O
"	O
machine-oriented	O
"	O
programming	O
language	O
based	O
on	O
PL/I	B-Language
.	O
</s>
<s>
It	O
was	O
developed	O
by	O
IBM	O
in	O
the	O
late	O
1960s	O
,	O
under	O
the	O
name	O
Basic	O
Systems	O
Language	O
(	O
BSL	O
)	O
,	O
as	O
a	O
replacement	O
for	O
assembly	B-Language
language	I-Language
on	O
internal	O
software	O
projects	O
;	O
it	O
included	O
support	O
for	O
inline	B-Language
assembly	I-Language
and	O
explicit	O
control	O
over	O
register	B-General_Concept
usage	O
.	O
</s>
<s>
Early	O
projects	O
using	O
PL/S	B-Language
were	O
the	O
batch	O
utility	O
,	O
IEHMOVE	O
,	O
and	O
the	O
Time	B-Application
Sharing	I-Application
Option	I-Application
of	O
MVT	O
,	O
TSO	O
.	O
</s>
<s>
By	O
the	O
1970s	O
,	O
IBM	O
was	O
rewriting	O
its	O
flagship	O
operating	O
system	O
in	O
PL/S	B-Language
.	O
</s>
<s>
Although	O
users	O
frequently	O
asked	O
IBM	O
to	O
release	O
PL/S	B-Language
for	O
their	O
use	O
,	O
IBM	O
refused	O
saying	O
that	O
the	O
product	O
was	O
proprietary	O
.	O
</s>
<s>
Their	O
concern	O
was	O
that	O
open	O
PL/S	B-Language
would	O
give	O
competitors	O
,	O
Amdahl	O
,	O
Itel	O
(	O
National	O
Advanced	O
Systems	O
)	O
,	O
Storage	B-Application
Technology	I-Application
Corporation	I-Application
,	O
Trilogy	O
Systems	O
,	O
Magnuson	O
Computer	O
Systems	O
,	O
Fujitsu	O
,	O
Hitachi	O
,	O
and	O
other	O
PCM	B-Device
vendors	O
a	O
competitive	O
advantage	O
.	O
</s>
<s>
However	O
,	O
even	O
though	O
they	O
refused	O
to	O
make	O
available	O
a	O
compiler	O
,	O
they	O
shipped	O
the	O
PL/S	B-Language
source	O
code	O
to	O
large	O
parts	O
of	O
the	O
OS	O
to	O
customers	O
,	O
many	O
of	O
whom	O
thus	O
became	O
familiar	O
with	O
reading	O
it	O
.	O
</s>
<s>
Closed	O
PL/S	B-Language
meant	O
that	O
only	O
IBM	O
could	O
easily	O
modify	O
and	O
enhance	O
the	O
operating	O
system	O
.	O
</s>
<s>
PL/S	B-Language
was	O
succeeded	O
by	O
PL/S	B-Language
II	O
,	O
PL/S	B-Language
III	O
and	O
PL/AS	B-Language
(	O
Programming	O
Language/Advanced	O
Systems	O
)	O
,	O
and	O
then	O
PL/X	B-Language
(	O
Programming	O
Language/Cross	O
Systems	O
)	O
.	O
</s>
<s>
PL/DS	O
(	O
Programming	O
Language/Distributed	O
Systems	O
)	O
was	O
a	O
closely	O
related	O
language	O
used	O
to	O
develop	O
the	O
DPPX	B-Operating_System
operating	O
system	O
,	O
and	O
PL/DS	O
II	O
was	O
a	O
port	O
of	O
the	O
S/370	O
architecture	O
for	O
the	O
DPPX/370	O
port	O
.	O
</s>
<s>
As	O
the	O
market	O
for	O
computers	O
and	O
software	O
shifted	O
away	O
from	O
IBM	O
mainframes	O
and	O
MVS	B-Application
,	O
IBM	O
recanted	O
and	O
has	O
offered	O
the	O
current	O
versions	O
of	O
PL/S	B-Language
to	O
select	O
customers	O
(	O
ISVs	O
through	O
the	O
Developer	O
Partner	O
program	O
.	O
)	O
</s>
<s>
The	O
Rand	O
RL/S	O
compiler	O
for	O
IBM	O
’s	O
PL/S	B-Language
language	O
was	O
developed	O
in	O
the	O
early	O
1970s	O
by	O
the	O
Computation	O
Center	O
of	O
the	O
Rand	O
Corporation	O
in	O
Santa	O
Monica	O
,	O
CA	O
.	O
</s>
<s>
It	O
was	O
implemented	O
using	O
the	O
XPL	B-Language
compiler	O
generator	O
system	O
by	O
a	O
team	O
of	O
three	O
Rand	O
programmers	O
(	O
R	O
.	O
Lawrence	O
Clark	O
,	O
James	O
S	O
.	O
Reiley	O
,	O
and	O
the	O
team	O
leader	O
David	O
J	O
.	O
Smith	O
)	O
.	O
</s>
<s>
Only	O
publicly	O
available	O
,	O
non-copyrighted	O
PL/S	B-Language
documentation	O
and	O
PL/S	B-Language
source	O
and	O
generated	O
assembler	B-Language
code	I-Language
examples	O
from	O
IBM	O
distributed	O
source	O
files	O
for	O
the	O
MVS	B-Application
operating	I-Application
system	I-Application
were	O
used	O
.	O
</s>
<s>
This	O
was	O
assured	O
by	O
parsing	O
many	O
thousands	O
of	O
lines	O
of	O
IBM	O
written	O
PL/S	B-Language
code	O
taken	O
from	O
the	O
MVS	B-Application
distribution	O
files	O
.	O
</s>
<s>
The	O
assembler	B-Language
language	I-Language
code	O
produced	O
by	O
the	O
Rand	O
RL/S	O
compiler	O
is	O
not	O
identical	O
to	O
the	O
code	O
produced	O
by	O
IBM	O
’s	O
PL/S	B-Language
compiler	O
,	O
but	O
it	O
is	O
functionally	O
equivalent	O
.	O
</s>
<s>
Rand	O
has	O
been	O
a	O
long-time	O
contributor	O
to	O
computer	O
research	O
and	O
development	O
(	O
e.g.	O
,	O
JOSS	B-Language
,	O
the	O
Rand	B-Device
tablet	I-Device
,	O
WYLBUR	B-Application
)	O
and	O
was	O
an	O
early	O
pioneer	O
in	O
the	O
definition	O
and	O
development	O
of	O
“	O
packet	O
switching	O
”	O
network	O
technology	O
(	O
)	O
.	O
</s>
<s>
Rand	O
’s	O
interest	O
in	O
PL/S	B-Language
derived	O
from	O
extensive	O
modifications	O
that	O
the	O
Computation	O
Center	O
had	O
made	O
to	O
IBM	O
’s	O
MVT	B-Application
operating	I-Application
system	I-Application
,	O
including	O
modifications	O
to	O
improve	O
the	O
performance	O
of	O
the	O
Arpanet	O
on	O
its	O
IBM	O
360	O
computer	O
.	O
</s>
<s>
Because	O
MVT	O
did	O
not	O
process	O
network	O
interrupts	O
quickly	O
enough	O
to	O
handle	O
the	O
Arpanet	O
traffic	O
,	O
a	O
“	O
hypervisor	B-Operating_System
”	O
was	O
developed	O
to	O
allow	O
Arpanet	O
interrupts	O
to	O
be	O
handled	O
by	O
specially	O
written	O
code	O
while	O
all	O
other	O
interrupts	O
were	O
handled	O
by	O
MVT	O
.	O
</s>
<s>
When	O
the	O
MVS	B-Application
operating	I-Application
system	I-Application
was	O
announced	O
by	O
IBM	O
,	O
Rand	O
volunteered	O
as	O
an	O
early	O
“	O
beta	O
”	O
site	O
for	O
the	O
operating	O
system	O
with	O
the	O
intent	O
of	O
porting	O
the	O
hypervisor	B-Operating_System
and	O
other	O
modifications	O
to	O
MVS	B-Application
.	O
</s>
<s>
As	O
is	O
well	O
,	O
IBM	O
,	O
however	O
,	O
refused	O
to	O
provide	O
its	O
PL/S	B-Language
compiler	O
to	O
customers	O
,	O
claiming	O
it	O
was	O
a	O
significant	O
competitive	O
advantage	O
.	O
</s>
<s>
Not	O
having	O
the	O
compiler	O
meant	O
that	O
neither	O
competitors	O
nor	O
customers	O
could	O
modify	O
the	O
MVS	B-Application
code	O
at	O
the	O
PL/S	B-Language
source	O
level	O
,	O
and	O
could	O
only	O
modify	O
the	O
generated	O
assembler	B-Language
code	I-Language
.	O
</s>
<s>
However	O
,	O
modifications	O
made	O
at	O
the	O
generated	O
assembler	B-Language
level	O
were	O
easily	O
obsoleted	O
when	O
IBM	O
modified	O
the	O
PL/S	B-Language
source	O
code	O
and	O
distributed	O
re-generated	O
assembler	B-Language
code	I-Language
.	O
</s>
<s>
This	O
was	O
particularly	O
true	O
of	O
modifications	O
to	O
PL/S	B-Language
generated	O
data	O
structures	O
.	O
</s>
<s>
Rand	O
,	O
therefore	O
,	O
decided	O
to	O
develop	O
its	O
own	O
version	O
of	O
a	O
PL/S	B-Language
compiler	O
to	O
meet	O
both	O
operational	O
objectives	O
and	O
contractual	O
commitments	O
.	O
</s>
<s>
The	O
RL/S	O
compiler	O
was	O
initially	O
written	O
in	O
PL/I	B-Language
and	O
later	O
converted	O
to	O
RL/S	O
to	O
improve	O
performance	O
.	O
</s>
<s>
With	O
few	O
restrictions	O
,	O
RL/S	O
programs	O
could	O
be	O
developed	O
using	O
IBM	O
’s	O
PL/I	B-Language
compiler	O
for	O
preprocessing	O
and	O
debugging	O
,	O
with	O
the	O
final	O
code	O
then	O
compiled	O
by	O
RL/S	O
.	O
</s>
<s>
A	O
fully	O
compliant	O
PL/S	B-Language
compiler	O
was	O
"	O
developed	O
"	O
by	O
Fujitsu	O
Ltd	O
in	O
the	O
late-1970s	O
,	O
adapting	O
IBM	O
's	O
PL/I	B-Language
Optimizer	O
compiler	O
source	O
code	O
as	O
its	O
starting	O
point	O
.	O
</s>
<s>
This	O
PL/S	B-Language
compiler	O
was	O
used	O
internally	O
by	O
Fujitsu	O
,	O
and	O
also	O
by	O
Fujitsu	O
's	O
external	O
affiliates	O
.	O
</s>
<s>
The	O
phase	O
names	O
of	O
this	O
PL/S	B-Language
compiler	O
were	O
the	O
same	O
as	O
the	O
corresponding	O
phase	O
names	O
of	O
IBM	O
's	O
PL/I	B-Language
Optimizer	O
compiler	O
,	O
with	O
the	O
initial	O
"	O
I	O
"	O
(	O
IBM	O
)	O
in	O
the	O
phase	O
name	O
being	O
replaced	O
by	O
an	O
initial	O
"	O
J	O
"	O
(	O
Japan	O
)	O
.	O
</s>
