<s>
RTL/2	B-Language
(	O
Real-Time	B-General_Concept
Language	O
)	O
is	O
a	O
discontinued	O
high-level	B-Language
programming	I-Language
language	I-Language
for	O
use	O
in	O
real-time	B-General_Concept
computing	I-General_Concept
,	O
developed	O
at	O
Imperial	O
Chemical	O
Industries	O
,	O
Ltd	O
.	O
(	O
ICI	O
)	O
,	O
by	O
J.G.P.	O
</s>
<s>
It	O
was	O
based	O
on	O
concepts	O
from	O
ALGOL	B-Language
68	I-Language
,	O
and	O
intended	O
to	O
be	O
small	O
and	O
simple	O
.	O
</s>
<s>
RTL/2	B-Language
was	O
standardised	O
in	O
1980	O
by	O
the	O
British	O
Standards	O
Institution	O
.	O
</s>
<s>
The	O
data	O
types	O
in	O
RTL/2	B-Language
were	O
strongly	O
typed	O
,	O
with	O
separate	O
compiling	B-Language
.	O
</s>
<s>
The	O
compilation	B-Language
units	I-Language
contained	O
one	O
or	O
more	O
items	O
named	O
bricks	O
,	O
i.e.	O
</s>
<s>
The	O
entry	O
mechanism	O
and	O
implementation	O
of	O
local	O
variables	O
was	O
reentrant	B-Operating_System
.	O
</s>
<s>
There	O
was	O
no	O
heap	O
or	O
garbage	B-General_Concept
collection	I-General_Concept
,	O
so	O
programmers	O
had	O
to	O
implement	O
memory	B-General_Concept
management	I-General_Concept
manually	O
.	O
</s>
<s>
A	O
stack	B-Application
brick	O
was	O
an	O
area	O
of	O
storage	O
reserved	O
for	O
running	O
all	O
the	O
procedures	O
of	O
a	O
single	O
process	O
and	O
contained	O
the	O
call	O
stack	B-Application
,	O
local	O
variables	O
and	O
other	O
housekeeping	O
items	O
.	O
</s>
<s>
The	O
extent	O
to	O
which	O
stack	B-Application
bricks	O
were	O
used	O
varied	O
depending	O
on	O
the	O
host	O
environment	O
in	O
which	O
RTL/2	B-Language
programs	O
ran	O
.	O
</s>
<s>
Access	O
to	O
the	O
host	O
environment	O
of	O
an	O
RTL/2	B-Language
program	O
was	O
provided	O
via	O
special	O
procedure	O
and	O
data	O
bricks	O
called	O
SVC	O
procedures	O
and	O
SVC	O
data	O
.	O
</s>
<s>
These	O
were	O
accessible	O
in	O
RTL/2	B-Language
but	O
implemented	O
in	O
some	O
other	O
language	O
in	O
the	O
host	O
environment	O
.	O
</s>
<s>
RTL/2	B-Language
compiles	B-Language
to	O
assembly	B-Language
language	I-Language
and	O
provides	O
the	O
CODE	O
statement	O
to	O
allow	O
including	O
assembly	B-Language
language	I-Language
in	O
RTL/2	B-Language
source	O
code	O
.	O
</s>
<s>
The	O
CODE	O
statement	O
takes	O
two	O
operands	O
:	O
the	O
number	O
of	O
bytes	O
used	O
by	O
the	O
code	O
insert	O
and	O
the	O
number	O
of	O
bytes	O
of	O
stack	B-Application
used	O
.	O
</s>
<s>
Within	O
code	O
statements	O
two	O
trip	O
characters	O
are	O
used	O
to	O
access	O
RTL/2	B-Language
variables	O
.	O
</s>
<s>
These	O
vary	O
between	O
different	O
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
On	O
a	O
Digital	O
Equipment	O
Corporation	O
(	O
DEC	O
)	O
PDP-11	B-Device
running	O
RSX-11M	O
,	O
and	O
a	O
VAX	B-Device
running	O
VMS	B-Operating_System
,	O
the	O
trip	O
characters	O
are	O
*	O
and	O
/	O
.	O
</s>
<s>
While	O
the	O
specifics	O
varied	O
by	O
operating	B-General_Concept
system	I-General_Concept
the	O
following	O
is	O
an	O
example	O
of	O
a	O
code	O
insert	O
on	O
VAX/VMS	B-Operating_System
:	O
</s>
<s>
This	O
code	O
insert	O
moves	O
the	O
value	O
of	O
a	O
variable	O
passed	O
into	O
the	O
RTL/2	B-Language
procedure	O
into	O
a	O
variable	O
named	O
COUNTER	O
in	O
a	O
data	O
brick	O
named	O
MYDATA	O
.	O
</s>
