<s>
Modula-2	B-Language
is	O
a	O
structured	B-Language
,	O
procedural	B-Application
programming	I-Application
language	I-Application
developed	O
between	O
1977	O
and	O
1985/8	O
by	O
Niklaus	O
Wirth	O
at	O
ETH	O
Zurich	O
.	O
</s>
<s>
It	O
was	O
created	O
as	O
the	O
language	O
for	O
the	O
operating	B-General_Concept
system	I-General_Concept
and	O
application	B-Application
software	I-Application
of	O
the	O
Lilith	B-Device
personal	B-Device
workstation	I-Device
.	O
</s>
<s>
It	O
was	O
later	O
used	O
for	O
programming	O
outside	O
the	O
context	O
of	O
the	O
Lilith	B-Device
.	O
</s>
<s>
Wirth	O
viewed	O
Modula-2	B-Language
as	O
a	O
successor	O
to	O
his	O
earlier	O
programming	O
languages	O
Pascal	B-Application
and	O
Modula	B-Language
.	O
</s>
<s>
The	O
language	O
design	O
was	O
influenced	O
by	O
the	O
Mesa	B-Language
language	O
and	O
the	O
Xerox	B-Device
Alto	I-Device
,	O
both	O
from	O
Xerox	O
PARC	O
,	O
that	O
Wirth	O
saw	O
during	O
his	O
1976	O
sabbatical	O
year	O
there	O
.	O
</s>
<s>
Modula-2	B-Language
was	O
followed	O
by	O
Modula-3	B-Language
,	O
and	O
later	O
by	O
the	O
Oberon	B-Language
series	O
of	O
languages	O
.	O
</s>
<s>
Modula-2	B-Language
is	O
a	O
general	O
purpose	O
procedural	B-Application
language	I-Application
suitable	O
for	O
both	O
systems	B-Application
programming	I-Application
and	O
applications	O
programming	O
.	O
</s>
<s>
The	O
syntax	O
is	O
based	O
on	O
Wirth	O
's	O
earlier	O
language	O
,	O
Pascal	B-Application
,	O
with	O
some	O
elements	O
and	O
syntactic	O
ambiguities	O
removed	O
.	O
</s>
<s>
The	O
module	B-Architecture
concept	O
,	O
designed	O
to	O
support	O
separate	O
compilation	B-Language
and	O
data	O
abstraction	O
;	O
and	O
direct	O
language	O
support	O
for	O
multiprogramming	O
were	O
added	O
.	O
</s>
<s>
The	O
language	O
allows	O
the	O
use	O
of	O
one-pass	B-Language
compilers	I-Language
.	O
</s>
<s>
Such	O
a	O
compiler	B-Language
by	O
Gutknecht	O
and	O
Wirth	O
was	O
about	O
four	O
times	O
faster	O
than	O
earlier	O
multi-pass	B-Application
compilers	I-Application
.	O
</s>
<s>
A	O
Modula-2	B-Language
module	B-Architecture
may	O
be	O
used	O
to	O
encapsulate	O
a	O
set	O
of	O
related	O
subprograms	O
and	O
data	O
structures	O
,	O
and	O
restrict	O
their	O
visibility	B-Application
from	O
other	O
parts	O
of	O
the	O
program	O
.	O
</s>
<s>
Modula-2	B-Language
programs	O
are	O
composed	O
of	O
modules	B-Architecture
,	O
each	O
of	O
which	O
is	O
made	O
up	O
of	O
two	O
parts	O
:	O
a	O
definition	O
module	B-Architecture
,	O
the	O
interface	O
portion	O
,	O
which	O
contains	O
only	O
those	O
parts	O
of	O
the	O
subsystem	O
that	O
are	O
exported	O
(	O
visible	O
to	O
other	O
modules	B-Architecture
)	O
,	O
and	O
an	O
implementation	O
module	B-Architecture
,	O
which	O
contains	O
the	O
working	O
code	O
that	O
is	O
internal	O
to	O
the	O
module	B-Architecture
.	O
</s>
<s>
The	O
language	O
has	O
strict	O
scope	B-Language
control	O
.	O
</s>
<s>
Except	O
for	O
standard	O
identifiers	O
,	O
no	O
object	O
from	O
the	O
outside	O
is	O
visible	O
inside	O
a	O
module	B-Architecture
unless	O
explicitly	O
imported	O
;	O
no	O
internal	O
module	B-Architecture
object	O
is	O
visible	O
from	O
the	O
outside	O
unless	O
explicitly	O
exported	O
.	O
</s>
<s>
Then	O
the	O
objects	O
a	O
,	O
b	O
,	O
c	B-Language
,	O
and	O
P	O
from	O
module	B-Architecture
M1	O
are	O
known	O
outside	O
module	B-Architecture
M1	O
as	O
M1.a	O
,	O
M1.b	O
,	O
M1.c	O
,	O
and	O
M1.P	O
.	O
</s>
<s>
They	O
are	O
exported	O
in	O
a	O
qualified	O
manner	O
to	O
the	O
outside	O
(	O
assuming	O
module	B-Architecture
M1	O
is	O
global	O
)	O
.	O
</s>
<s>
The	O
exporting	O
module	B-Architecture
's	O
name	O
,	O
i.e.	O
</s>
<s>
Then	O
this	O
means	O
that	O
the	O
objects	O
exported	O
by	O
module	B-Architecture
M1	O
to	O
the	O
outside	O
of	O
its	O
enclosing	O
program	O
can	O
now	O
be	O
used	O
inside	O
module	B-Architecture
M2	O
.	O
</s>
<s>
They	O
are	O
referenced	O
in	O
a	O
qualified	O
manner	O
:	O
M1.a	O
,	O
M1.b	O
,	O
M1.c	O
,	O
and	O
M1.P	O
.	O
</s>
<s>
For	O
example	O
,	O
if	O
another	O
module	B-Architecture
M3	O
exports	O
an	O
object	O
called	O
P	O
,	O
then	O
the	O
two	O
objects	O
can	O
be	O
distinguished	O
since	O
M1.P	O
differs	O
from	O
M3.P	O
.	O
</s>
<s>
It	O
does	O
not	O
matter	O
that	O
both	O
objects	O
are	O
called	O
P	O
inside	O
their	O
exporting	O
modules	B-Architecture
M1	O
and	O
M3	O
.	O
</s>
<s>
Suppose	O
module	B-Architecture
M4	O
is	O
formulated	O
as	O
this	O
:	O
</s>
<s>
This	O
means	O
that	O
objects	O
exported	O
by	O
module	B-Architecture
M1	O
to	O
the	O
outside	O
can	O
again	O
be	O
used	O
inside	O
module	B-Architecture
M4	O
,	O
but	O
now	O
by	O
mere	O
references	O
to	O
the	O
exported	O
identifiers	O
in	O
an	O
unqualified	O
manner	O
as	O
:	O
a	O
,	O
b	O
,	O
c	B-Language
,	O
and	O
P	O
.	O
Example	O
:	O
</s>
<s>
It	O
allows	O
variables	O
and	O
other	O
objects	O
to	O
be	O
used	O
outside	O
their	O
exporting	O
module	B-Architecture
in	O
the	O
same	O
unqualified	O
,	O
manner	O
as	O
inside	O
the	O
exporting	O
module	B-Architecture
.	O
</s>
<s>
This	O
property	O
helps	O
with	O
the	O
maintenance	O
of	O
large	O
programs	O
containing	O
many	O
modules	B-Architecture
.	O
</s>
<s>
The	O
language	O
provides	O
for	O
single-processor	O
concurrency	B-Architecture
(	O
monitors	O
,	O
coroutines	B-Architecture
and	O
explicit	O
transfer	O
of	O
control	O
)	O
and	O
for	O
hardware	O
access	O
(	O
absolute	O
addresses	O
,	O
bit	O
manipulation	O
,	O
and	O
interrupts	B-Application
)	O
.	O
</s>
<s>
There	O
are	O
two	O
major	O
dialects	O
of	O
Modula-2	B-Language
.	O
</s>
<s>
The	O
first	O
is	O
PIM	O
,	O
named	O
for	O
the	O
book	O
Programming	O
in	O
Modula-2	B-Language
by	O
Niklaus	O
Wirth	O
.	O
</s>
<s>
Required	O
explicit	O
EXPORT	O
clause	O
in	O
definition	O
modules	B-Architecture
.	O
</s>
<s>
Removed	O
the	O
EXPORT	O
clause	O
from	O
definition	O
modules	B-Architecture
following	O
the	O
observation	O
that	O
everything	O
within	O
a	O
definition	O
module	B-Architecture
defines	O
the	O
interface	O
to	O
that	O
module	B-Architecture
,	O
hence	O
the	O
EXPORT	O
clause	O
was	O
redundant	O
.	O
</s>
<s>
ISO	O
Modula-2	B-Language
resolved	O
most	O
of	O
the	O
ambiguities	O
in	O
PIM	O
Modula-2	B-Language
.	O
</s>
<s>
It	O
added	O
the	O
data	O
types	O
COMPLEX	O
and	O
LONGCOMPLEX	O
,	O
exceptions	O
,	O
module	B-Architecture
termination	O
(	O
FINALLY	O
clause	O
)	O
and	O
a	O
complete	O
standard	O
input/output	B-General_Concept
(	O
I/O	B-General_Concept
)	O
library	B-Library
.	O
</s>
<s>
There	O
are	O
several	O
supersets	O
of	O
Modula-2	B-Language
with	O
language	O
extensions	O
for	O
specific	O
application	O
domains	O
:	O
</s>
<s>
There	O
are	O
several	O
derivative	O
languages	O
that	O
resemble	O
Modula-2	B-Language
very	O
closely	O
but	O
are	O
new	O
languages	O
in	O
their	O
own	O
right	O
.	O
</s>
<s>
Oberon	B-Language
,	O
developed	O
at	O
ETH	O
Zürich	O
for	O
System	B-Application
Oberon	I-Application
.	O
</s>
<s>
Active	B-Language
Oberon	I-Language
,	O
yet	O
another	O
object-oriented	B-Language
Extension	O
of	O
Oberon	B-Language
,	O
developed	O
also	O
at	O
ETH	O
with	O
the	O
main	O
objective	O
to	O
support	O
parallel	O
programming	O
on	O
multiprocessor	O
and	O
multicore	O
systems	O
.	O
</s>
<s>
Many	O
other	O
current	O
programming	O
languages	O
have	O
adopted	O
features	O
of	O
Modula-2	B-Language
.	O
</s>
<s>
Modula-2	B-Language
is	O
used	O
to	O
program	O
many	O
embedded	B-Architecture
systems	I-Architecture
.	O
</s>
<s>
Cambridge	O
Modula-2	B-Language
by	O
Cambridge	O
Microprocessor	O
Systems	O
is	O
based	O
on	O
a	O
subset	O
of	O
PIM4	O
with	O
language	O
extensions	O
for	O
embedded	O
development	O
.	O
</s>
<s>
The	O
compiler	B-Language
runs	O
on	O
DOS	B-Device
and	O
it	O
generates	O
code	O
for	O
Motorola	B-Device
68000	I-Device
series	I-Device
(	O
M68k	B-Device
)	O
based	O
embedded	O
microcontrollers	O
running	O
a	O
MINOS	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
Mod51	O
by	O
Mandeno	O
Granville	O
Electronics	O
is	O
based	O
on	O
ISO	O
Modula-2	B-Language
with	O
language	O
extensions	O
for	O
embedded	O
development	O
following	O
IEC	O
1131	O
,	O
an	O
industry	O
standard	O
for	O
programmable	B-Architecture
logic	I-Architecture
controllers	I-Architecture
(	O
PLC	O
)	O
closely	O
related	O
to	O
Modula-2	B-Language
.	O
</s>
<s>
The	O
Mod51	O
compiler	B-Language
generates	O
standalone	O
code	O
for	O
80C51	O
based	O
microcontrollers	O
.	O
</s>
<s>
Delco	O
Electronics	O
,	O
then	O
a	O
subsidiary	O
of	O
GM	O
Hughes	O
Electronics	O
,	O
developed	O
a	O
version	O
of	O
Modula-2	B-Language
for	O
embedded	B-Architecture
control	I-Architecture
systems	O
starting	O
in	O
1985	O
.	O
</s>
<s>
Delco	O
named	O
it	O
Modula-GM	O
.	O
</s>
<s>
It	O
was	O
the	O
first	O
high-level	B-Language
programming	I-Language
language	I-Language
used	O
to	O
replace	O
machine	B-Language
code	I-Language
(	O
language	O
)	O
for	O
embedded	B-Architecture
systems	I-Architecture
in	O
Delco	O
's	O
engine	O
control	O
units	O
(	O
ECUs	O
)	O
.	O
</s>
<s>
The	O
first	O
experimental	O
use	O
of	O
Modula-GM	O
in	O
an	O
embedded	B-Architecture
controller	I-Architecture
was	O
in	O
the	O
1985	O
Antilock	O
Braking	O
System	O
Controller	O
which	O
was	O
based	O
on	O
the	O
Motorola	O
68xxx	O
microprocessor	O
,	O
and	O
in	O
1993	O
Gen-4	O
ECU	O
used	O
by	O
the	O
Champ	O
Car	O
World	O
Series	O
Championship	O
Auto	O
Racing	O
Teams	O
(	O
CART	O
)	O
and	O
Indy	O
Racing	O
League	O
(	O
IRL	O
)	O
teams	O
.	O
</s>
<s>
The	O
first	O
production	O
use	O
of	O
Modula-GM	O
was	O
its	O
use	O
in	O
GM	O
trucks	O
starting	O
with	O
the	O
1990	O
model	O
year	O
vehicle	O
control	O
module	B-Architecture
(	O
VCM	O
)	O
used	O
to	O
manage	O
GM	O
Powertrain	O
's	O
Vortec	O
engines	O
.	O
</s>
<s>
Modula-GM	O
was	O
also	O
used	O
on	O
all	O
ECUs	O
for	O
GM	O
's	O
90°	O
Buick	O
V6	O
engine	O
family	O
3800	O
Series	O
II	O
used	O
in	O
the	O
1997-2005	O
model	O
year	O
Buick	O
Park	O
Avenue	O
.	O
</s>
<s>
The	O
Modula-GM	O
compilers	B-Language
and	O
associated	O
software	O
management	O
tools	O
were	O
sourced	O
by	O
Delco	O
from	O
Intermetrics	O
.	O
</s>
<s>
Modula-2	B-Language
was	O
selected	O
as	O
the	O
basis	O
for	O
Delco	O
's	O
high	B-Language
level	I-Language
language	I-Language
because	O
of	O
its	O
many	O
strengths	O
over	O
other	O
alternative	O
language	O
choices	O
in	O
1986	O
.	O
</s>
<s>
ECU	O
embedded	O
software	O
now	O
developed	O
at	O
Delphi	O
is	O
compiled	B-Language
with	O
commercial	O
compilers	B-Language
for	O
the	O
language	O
C	B-Language
.	O
</s>
<s>
The	O
satellites	O
of	O
the	O
Russian	O
radionavigation-satellite	O
service	O
framework	O
GLONASS	O
,	O
similar	O
to	O
the	O
United	O
States	O
Global	O
Positioning	O
System	O
(	O
GPS	O
)	O
,	O
are	O
programmed	O
in	O
Modula-2	B-Language
.	O
</s>
<s>
Turbo	O
Modula-2	B-Language
was	O
a	O
compiler	B-Language
and	O
an	O
integrated	B-Application
development	I-Application
environment	I-Application
for	O
MS-DOS	B-Application
developed	O
,	O
but	O
not	O
published	O
,	O
by	O
Borland	O
.	O
</s>
<s>
Jensen	O
and	O
Partners	O
,	O
which	O
included	O
Borland	O
cofounder	O
Niels	O
Jensen	O
,	O
bought	O
the	O
unreleased	O
codebase	O
and	O
turned	O
it	O
into	O
TopSpeed	O
Modula-2	B-Language
.	O
</s>
<s>
It	O
was	O
eventually	O
sold	O
to	O
Clarion	B-Language
,	O
now	O
SoftVelocity	B-Language
,	O
who	O
then	O
offered	O
the	O
Modula-2	B-Language
compiler	B-Language
as	O
part	O
of	O
its	O
Clarion	B-Language
product	O
line	O
at	O
that	O
time	O
.	O
</s>
<s>
A	O
Zilog	B-General_Concept
Z80	I-General_Concept
CP/M	B-Application
version	O
of	O
Turbo	O
Modula-2	B-Language
was	O
briefly	O
marketed	O
by	O
Echelon	O
under	O
license	O
from	O
Borland	O
.	O
</s>
<s>
A	O
companion	O
release	O
for	O
Hitachi	B-General_Concept
HD64180	I-General_Concept
was	O
sold	O
by	O
Micromint	O
as	O
a	O
development	O
tool	O
for	O
their	O
SB-180	O
single-board	O
computer	O
.	O
</s>
<s>
IBM	O
had	O
a	O
Modula-2	B-Language
compiler	B-Language
for	O
internal	O
use	O
which	O
ran	O
on	O
both	O
OS/2	B-Application
and	O
AIX	B-Application
,	O
and	O
had	O
first	O
class	O
support	O
in	O
IBM	O
's	O
E2	B-Application
editor	O
.	O
</s>
<s>
IBM	O
Modula-2	B-Language
was	O
used	O
for	O
parts	O
of	O
the	O
OS/400	B-Application
Vertical	O
Licensed	O
Internal	O
Code	O
(	O
effectively	O
the	O
kernel	O
of	O
OS/400	B-Application
)	O
.	O
</s>
<s>
This	O
code	O
was	O
mostly	O
replaced	O
with	O
C++	B-Language
when	O
OS/400	B-Application
was	O
ported	O
to	O
the	O
IBM	B-Device
RS64	I-Device
processor	O
family	O
,	O
although	O
some	O
remains	O
in	O
modern	O
releases	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
A	O
Motorola	B-Device
68000	I-Device
backend	O
also	O
existed	O
,	O
which	O
may	O
have	O
been	O
used	O
in	O
embedded	B-Architecture
systems	I-Architecture
products	O
.	O
</s>
<s>
Modula-2	B-Language
is	O
used	O
to	O
program	O
some	O
operating	B-General_Concept
systems	I-General_Concept
(	O
OSs	O
)	O
.	O
</s>
<s>
The	O
Modula-2	B-Language
module	B-Architecture
structure	O
and	O
support	O
are	O
used	O
directly	O
in	O
two	O
related	O
OSs	O
.	O
</s>
<s>
The	O
OS	O
named	O
Medos-2	O
,	O
for	O
the	O
Lilith	B-Device
workstation	B-Device
,	O
was	O
developed	O
at	O
ETH	O
Zurich	O
,	O
by	O
Svend	O
Erik	O
Knudsen	O
with	O
advice	O
from	O
Wirth	O
.	O
</s>
<s>
It	O
is	O
a	O
single	O
user	O
,	O
object-oriented	B-Application
operating	I-Application
system	I-Application
built	O
from	O
Modula-2	B-Language
modules	B-Architecture
.	O
</s>
<s>
The	O
OS	O
named	O
Excelsior	O
,	O
for	O
the	O
Kronos	B-Device
workstation	B-Device
,	O
was	O
developed	O
by	O
the	O
Academy	O
of	O
Sciences	O
of	O
the	O
Soviet	O
Union	O
,	O
Siberian	O
branch	O
,	O
Novosibirsk	O
Computing	O
Center	O
,	O
Modular	B-Architecture
Asynchronous	O
Developable	O
Systems	O
(	O
MARS	O
)	O
project	O
,	O
Kronos	B-Device
Research	O
Group	O
(	O
KRG	O
)	O
.	O
</s>
<s>
It	O
is	O
a	O
single	O
user	O
system	O
based	O
on	O
Modula-2	B-Language
modules	B-Architecture
.	O
</s>
<s>
Uses	O
ISO-standard	O
Modula-2	B-Language
.	O
</s>
