<s>
Erlang	B-Operating_System
(	O
)	O
is	O
a	O
general-purpose	B-Language
,	O
concurrent	B-Architecture
,	O
functional	B-Language
high-level	B-Language
programming	I-Language
language	I-Language
,	O
and	O
a	O
garbage-collected	B-General_Concept
runtime	B-Device
system	I-Device
.	O
</s>
<s>
The	O
term	O
Erlang	B-Operating_System
is	O
used	O
interchangeably	O
with	O
Erlang/OTP	B-Operating_System
,	O
or	O
Open	B-Language
Telecom	I-Language
Platform	I-Language
(	O
OTP	O
)	O
,	O
which	O
consists	O
of	O
the	O
Erlang	B-Operating_System
runtime	B-Device
system	I-Device
,	O
several	O
ready-to-use	O
components	O
(	O
OTP	O
)	O
mainly	O
written	O
in	O
Erlang	B-Operating_System
,	O
and	O
a	O
set	O
of	O
design	B-Architecture
principles	I-Architecture
for	O
Erlang	B-Operating_System
programs	O
.	O
</s>
<s>
The	O
Erlang	B-Operating_System
runtime	B-Device
system	I-Device
is	O
designed	O
for	O
systems	O
with	O
these	O
traits	O
:	O
</s>
<s>
The	O
Erlang	B-Operating_System
programming	I-Operating_System
language	I-Operating_System
has	O
immutable	B-Application
data	O
,	O
pattern	B-Language
matching	I-Language
,	O
and	O
functional	B-Language
programming	I-Language
.	O
</s>
<s>
The	O
sequential	O
subset	O
of	O
the	O
Erlang	B-Operating_System
language	I-Operating_System
supports	O
eager	O
evaluation	O
,	O
single	O
assignment	O
,	O
and	O
dynamic	O
typing	O
.	O
</s>
<s>
A	O
normal	O
Erlang	B-Operating_System
application	O
is	O
built	O
out	O
of	O
hundreds	O
of	O
small	O
Erlang	B-Operating_System
processes	B-Operating_System
.	O
</s>
<s>
It	O
was	O
originally	O
proprietary	B-Application
software	I-Application
within	O
Ericsson	O
,	O
developed	O
by	O
Joe	O
Armstrong	O
,	O
Robert	O
Virding	O
,	O
and	O
Mike	O
Williams	O
in	O
1986	O
,	O
but	O
was	O
released	O
as	O
free	B-License
and	I-License
open-source	I-License
software	I-License
in	O
1998	O
.	O
</s>
<s>
Erlang/OTP	B-Operating_System
is	O
supported	O
and	O
maintained	O
by	O
the	O
Open	B-Language
Telecom	I-Language
Platform	I-Language
(	O
OTP	O
)	O
product	O
unit	O
at	O
Ericsson	O
.	O
</s>
<s>
The	O
name	O
Erlang	B-Operating_System
,	O
attributed	O
to	O
Bjarne	O
Däcker	O
,	O
has	O
been	O
presumed	O
by	O
those	O
working	O
on	O
the	O
telephony	O
switches	O
(	O
for	O
whom	O
the	O
language	O
was	O
designed	O
)	O
to	O
be	O
a	O
reference	O
to	O
Danish	O
mathematician	O
and	O
engineer	O
Agner	O
Krarup	O
Erlang	B-Operating_System
and	O
a	O
syllabic	O
abbreviation	O
of	O
"	O
Ericsson	O
Language	O
"	O
.	O
</s>
<s>
Erlang	B-Operating_System
was	O
designed	O
with	O
the	O
aim	O
of	O
improving	O
the	O
development	O
of	O
telephony	O
applications	O
.	O
</s>
<s>
The	O
initial	O
version	O
of	O
Erlang	B-Operating_System
was	O
implemented	O
in	O
Prolog	B-Language
and	O
was	O
influenced	O
by	O
the	O
programming	O
language	O
PLEX	B-Language
used	O
in	O
earlier	O
Ericsson	O
exchanges	O
.	O
</s>
<s>
By	O
1988	O
Erlang	B-Operating_System
had	O
proven	O
that	O
it	O
was	O
suitable	O
for	O
prototyping	O
telephone	O
exchanges	O
,	O
but	O
the	O
Prolog	B-Language
interpreter	O
was	O
far	O
too	O
slow	O
.	O
</s>
<s>
In	O
1992	O
,	O
work	O
began	O
on	O
the	O
BEAM	B-Application
virtual	O
machine	O
(	O
VM	O
)	O
which	O
compiles	O
Erlang	B-Operating_System
to	O
C	O
using	O
a	O
mix	O
of	O
natively	O
compiled	O
code	O
and	O
threaded	B-Application
code	I-Application
to	O
strike	O
a	O
balance	O
between	O
performance	O
and	O
disk	O
space	O
.	O
</s>
<s>
According	O
to	O
co-inventor	O
Joe	O
Armstrong	O
,	O
the	O
language	O
went	O
from	O
lab	O
product	O
to	O
real	O
applications	O
following	O
the	O
collapse	O
of	O
the	O
next-generation	O
AXE	B-Device
telephone	I-Device
exchange	I-Device
named	O
AXE-N	O
in	O
1995	O
.	O
</s>
<s>
As	O
a	O
result	O
,	O
Erlang	B-Operating_System
was	O
chosen	O
for	O
the	O
next	O
Asynchronous	B-Operating_System
Transfer	O
Mode	O
(	O
ATM	O
)	O
exchange	O
AXD	O
.	O
</s>
<s>
In	O
February	O
1998	O
,	O
Ericsson	O
Radio	O
Systems	O
banned	O
the	O
in-house	O
use	O
of	O
Erlang	B-Operating_System
for	O
new	O
products	O
,	O
citing	O
a	O
preference	O
for	O
non-proprietary	O
languages	O
.	O
</s>
<s>
In	O
March	O
1998	O
Ericsson	O
announced	O
the	O
AXD301	O
switch	O
,	O
containing	O
over	O
a	O
million	O
lines	O
of	O
Erlang	B-Operating_System
and	O
reported	O
to	O
achieve	O
a	O
high	O
availability	O
of	O
nine	O
"	O
9	O
"	O
s	O
.	O
In	O
December	O
1998	O
,	O
the	O
implementation	O
of	O
Erlang	B-Operating_System
was	O
open-sourced	O
and	O
most	O
of	O
the	O
Erlang	B-Operating_System
team	O
resigned	O
to	O
form	O
a	O
new	O
company	O
Bluetail	O
AB	O
.	O
</s>
<s>
In	O
2006	O
,	O
native	O
symmetric	B-Operating_System
multiprocessing	I-Operating_System
support	O
was	O
added	O
to	O
the	O
runtime	B-Device
system	I-Device
and	O
VM	O
.	O
</s>
<s>
Erlang	B-Operating_System
applications	O
are	O
built	O
of	O
very	O
lightweight	O
Erlang	B-Operating_System
processes	B-Operating_System
in	O
the	O
Erlang	B-Operating_System
runtime	B-Device
system	I-Device
.	O
</s>
<s>
Erlang	B-Operating_System
processes	B-Operating_System
can	O
be	O
seen	O
as	O
"	O
living	O
"	O
objects	O
(	O
object-oriented	B-Language
programming	I-Language
)	O
,	O
with	O
data	O
encapsulation	O
and	O
message	B-Architecture
passing	I-Architecture
,	O
but	O
capable	O
of	O
changing	O
behavior	O
during	O
runtime	O
.	O
</s>
<s>
The	O
Erlang	B-Operating_System
runtime	B-Device
system	I-Device
provides	O
strict	O
process	O
isolation	O
between	O
Erlang	B-Operating_System
processes	B-Operating_System
(	O
this	O
includes	O
data	O
and	O
garbage	B-General_Concept
collection	I-General_Concept
,	O
separated	O
individually	O
by	O
each	O
Erlang	B-Operating_System
process	O
)	O
and	O
transparent	O
communication	O
between	O
processes	B-Operating_System
(	O
see	O
Location	B-Protocol
transparency	I-Protocol
)	O
on	O
different	O
Erlang	B-Operating_System
nodes	O
(	O
on	O
different	O
hosts	O
)	O
.	O
</s>
<s>
Joe	O
Armstrong	O
,	O
co-inventor	O
of	O
Erlang	B-Operating_System
,	O
summarized	O
the	O
principles	O
of	O
processes	B-Operating_System
in	O
his	O
PhD	O
thesis	O
:	O
</s>
<s>
Processes	B-Operating_System
are	O
strongly	O
isolated	O
.	O
</s>
<s>
Message	B-Architecture
passing	I-Architecture
is	O
the	O
only	O
way	O
for	O
processes	B-Operating_System
to	O
interact	O
.	O
</s>
<s>
Processes	B-Operating_System
have	O
unique	O
names	O
.	O
</s>
<s>
Processes	B-Operating_System
share	O
no	O
resources	O
.	O
</s>
<s>
Error	B-General_Concept
handling	I-General_Concept
is	O
non-local	O
.	O
</s>
<s>
Processes	B-Operating_System
do	O
what	O
they	O
are	O
supposed	O
to	O
do	O
or	O
fail	O
.	O
</s>
<s>
Joe	O
Armstrong	O
remarked	O
in	O
an	O
interview	O
with	O
Rackspace	O
in	O
2013	O
:	O
"	O
If	O
Java	B-Language
is	O
'	O
write	O
once	O
,	O
run	O
anywhere	O
 '	O
,	O
then	O
Erlang	B-Operating_System
is	O
'	O
write	O
once	O
,	O
run	O
forever	O
 '	O
.	O
"	O
</s>
<s>
In	O
2014	O
,	O
Ericsson	O
reported	O
Erlang	B-Operating_System
was	O
being	O
used	O
in	O
its	O
support	O
nodes	O
,	O
and	O
in	O
GPRS	B-General_Concept
,	O
3G	B-Architecture
and	O
LTE	O
mobile	O
networks	O
worldwide	O
and	O
also	O
by	O
Nortel	O
and	O
T-Mobile	O
.	O
</s>
<s>
Erlang	B-Operating_System
is	O
used	O
in	O
RabbitMQ	B-Application
.	O
</s>
<s>
Erlang	B-Operating_System
is	O
the	O
programming	O
language	O
used	O
to	O
code	O
WhatsApp	B-Application
.	O
</s>
<s>
Elixir	B-Language
is	O
a	O
programming	O
language	O
that	O
compiles	O
into	O
BEAM	B-Application
byte	O
code	O
(	O
via	O
Erlang	B-Operating_System
Abstract	O
Format	O
)	O
.	O
</s>
<s>
Since	O
being	O
released	O
as	O
open	O
source	O
,	O
Erlang	B-Operating_System
has	O
been	O
spreading	O
beyond	O
telecoms	O
,	O
establishing	O
itself	O
in	O
other	O
vertical	O
markets	O
such	O
as	O
FinTech	O
,	O
gaming	O
,	O
healthcare	O
,	O
automotive	O
,	O
internet	O
of	O
things	O
and	O
blockchain	O
.	O
</s>
<s>
Apart	O
from	O
WhatsApp	B-Application
,	O
there	O
are	O
other	O
companies	O
listed	O
as	O
Erlang	B-Operating_System
's	O
success	O
stories	O
:	O
Vocalink	O
(	O
a	O
MasterCard	O
company	O
)	O
,	O
Goldman	O
Sachs	O
,	O
Nintendo	O
,	O
AdRoll	O
,	O
Grindr	B-Application
,	O
BT	O
Mobile	O
,	O
Samsung	B-Application
,	O
OpenX	O
,	O
and	O
SITA	O
.	O
</s>
<s>
A	O
factorial	O
algorithm	O
implemented	O
in	O
Erlang	B-Operating_System
:	O
</s>
<s>
A	O
tail	O
recursive	O
algorithm	O
that	O
produces	O
the	O
Fibonacci	B-Algorithm
sequence	I-Algorithm
:	O
</s>
<s>
Quicksort	B-Algorithm
in	O
Erlang	B-Operating_System
,	O
using	O
list	B-Language
comprehension	I-Language
:	O
</s>
<s>
The	O
expression	O
[	O
Front	O
||	O
Front	O
<	O
-	O
Rest	O
,	O
Front	O
<	O
Pivot ]	O
is	O
a	O
list	B-Language
comprehension	I-Language
,	O
meaning	O
"	O
Construct	O
a	O
list	O
of	O
elements	O
Front	O
such	O
that	O
Front	O
is	O
a	O
member	O
of	O
Rest	O
,	O
and	O
Front	O
is	O
less	O
than	O
Pivot.	O
"	O
</s>
<s>
The	O
anonymous	B-General_Concept
function	I-General_Concept
is	O
named	O
Smaller	O
in	O
the	O
parameter	O
list	O
of	O
the	O
second	O
definition	O
of	O
qsort	O
so	O
that	O
it	O
can	O
be	O
referenced	O
by	O
that	O
name	O
within	O
that	O
function	O
.	O
</s>
<s>
Erlang	B-Operating_System
has	O
eight	O
primitive	O
data	O
types	O
:	O
</s>
<s>
(	O
This	O
is	O
called	O
arbitrary-precision	B-Algorithm
arithmetic	I-Algorithm
.	O
)	O
</s>
<s>
Atoms	O
are	O
never	O
garbage	B-General_Concept
collected	I-General_Concept
and	O
should	O
be	O
used	O
with	O
caution	O
,	O
especially	O
if	O
using	O
dynamic	O
atom	O
generation	O
.	O
</s>
<s>
They	O
are	O
created	O
by	O
evaluating	O
the	O
Erlang	B-Operating_System
primitive	O
make_ref( )	O
.	O
</s>
<s>
Erlang	B-Operating_System
primitives	O
exist	O
for	O
composing	O
and	O
decomposing	O
binaries	O
and	O
for	O
efficient	O
input/output	O
of	O
binaries	O
.	O
</s>
<s>
Pids	O
Pid	O
is	O
short	O
for	O
process	O
identifiera	O
Pid	O
is	O
created	O
by	O
the	O
Erlang	B-Operating_System
primitive	O
spawn( 	O
...	O
)	O
Pids	O
are	O
references	O
to	O
Erlang	B-Operating_System
processes	B-Operating_System
.	O
</s>
<s>
Funs	O
Funs	O
are	O
function	B-Language
closures	I-Language
.	O
</s>
<s>
Tuples	O
Tuples	O
are	O
containers	O
for	O
a	O
fixed	O
number	O
of	O
Erlang	B-Operating_System
data	O
types	O
.	O
</s>
<s>
Lists	O
Lists	O
are	O
containers	O
for	O
a	O
variable	O
number	O
of	O
Erlang	B-Operating_System
data	O
types	O
.	O
</s>
<s>
Erlang	B-Operating_System
has	O
no	O
method	O
to	O
define	O
classes	O
,	O
although	O
there	O
are	O
external	O
libraries	B-Library
available	O
.	O
</s>
<s>
Erlang	B-Operating_System
is	O
designed	O
with	O
a	O
mechanism	O
that	O
makes	O
it	O
easy	O
for	O
external	O
processes	B-Operating_System
to	O
monitor	O
for	O
crashes	O
(	O
or	O
hardware	O
failures	O
)	O
,	O
rather	O
than	O
an	O
in-process	O
mechanism	O
like	O
exception	B-General_Concept
handling	I-General_Concept
used	O
in	O
many	O
other	O
programming	O
languages	O
.	O
</s>
<s>
Crashes	O
are	O
reported	O
like	O
other	O
messages	O
,	O
which	O
is	O
the	O
only	O
way	O
processes	B-Operating_System
can	O
communicate	O
with	O
each	O
other	O
,	O
and	O
subprocesses	O
can	O
be	O
spawned	O
cheaply	O
(	O
see	O
below	O
)	O
.	O
</s>
<s>
Though	O
it	O
still	O
requires	O
handling	O
of	O
errors	O
,	O
this	O
philosophy	O
results	O
in	O
less	O
code	O
devoted	O
to	O
defensive	B-Application
programming	I-Application
where	O
error-handling	O
code	O
is	O
highly	O
contextual	O
and	O
specific	O
.	O
</s>
<s>
A	O
typical	O
Erlang	B-Operating_System
application	O
is	O
written	O
in	O
the	O
form	O
of	O
a	O
supervisor	O
tree	O
.	O
</s>
<s>
This	O
architecture	O
is	O
based	O
on	O
a	O
hierarchy	O
of	O
processes	B-Operating_System
in	O
which	O
the	O
top	O
level	O
process	O
is	O
known	O
as	O
a	O
"	O
supervisor	O
"	O
.	O
</s>
<s>
The	O
supervisor	O
then	O
spawns	O
multiple	O
child	O
processes	B-Operating_System
that	O
act	O
either	O
as	O
workers	O
or	O
more	O
,	O
lower	O
level	O
supervisors	O
.	O
</s>
<s>
Such	O
hierarchies	O
can	O
exist	O
to	O
arbitrary	O
depths	O
and	O
have	O
proven	O
to	O
provide	O
a	O
highly	O
scalable	O
and	O
fault-tolerant	B-General_Concept
environment	O
within	O
which	O
application	O
functionality	O
can	O
be	O
implemented	O
.	O
</s>
<s>
Within	O
a	O
supervisor	O
tree	O
,	O
all	O
supervisor	O
processes	B-Operating_System
are	O
responsible	O
for	O
managing	O
the	O
lifecycle	O
of	O
their	O
child	O
processes	B-Operating_System
,	O
and	O
this	O
includes	O
handling	O
situations	O
in	O
which	O
those	O
child	O
processes	B-Operating_System
crash	O
.	O
</s>
<s>
Any	O
process	O
can	O
become	O
a	O
supervisor	O
by	O
first	O
spawning	O
a	O
child	O
process	O
,	O
then	O
calling	O
erlang:monitor/2	O
on	O
that	O
process	O
.	O
</s>
<s>
Erlang	B-Operating_System
's	O
main	O
strength	O
is	O
support	O
for	O
concurrency	B-Operating_System
.	O
</s>
<s>
It	O
has	O
a	O
small	O
but	O
powerful	O
set	O
of	O
primitives	O
to	O
create	O
processes	B-Operating_System
and	O
communicate	O
among	O
them	O
.	O
</s>
<s>
Erlang	B-Operating_System
is	O
conceptually	O
similar	O
to	O
the	O
language	O
occam	B-Language
,	O
though	O
it	O
recasts	O
the	O
ideas	O
of	O
communicating	O
sequential	O
processes	B-Operating_System
(	O
CSP	O
)	O
in	O
a	O
functional	B-Language
framework	O
and	O
uses	O
asynchronous	B-Operating_System
message	B-Architecture
passing	I-Architecture
.	O
</s>
<s>
Processes	B-Operating_System
are	O
the	O
primary	O
means	O
to	O
structure	O
an	O
Erlang	B-Operating_System
application	O
.	O
</s>
<s>
They	O
are	O
neither	O
operating	B-General_Concept
system	I-General_Concept
processes	B-Operating_System
nor	O
threads	B-Operating_System
,	O
but	O
lightweight	B-Operating_System
processes	I-Operating_System
that	O
are	O
scheduled	O
by	O
BEAM	B-Application
.	O
</s>
<s>
Like	O
operating	B-General_Concept
system	I-General_Concept
processes	B-Operating_System
(	O
but	O
unlike	O
operating	B-General_Concept
system	I-General_Concept
threads	B-Operating_System
)	O
,	O
they	O
share	O
no	O
state	O
with	O
each	O
other	O
.	O
</s>
<s>
Thus	O
,	O
many	O
processes	B-Operating_System
can	O
be	O
created	O
without	O
degrading	O
performance	O
.	O
</s>
<s>
In	O
2005	O
,	O
a	O
benchmark	O
with	O
20	O
million	O
processes	B-Operating_System
was	O
successfully	O
performed	O
with	O
64-bit	O
Erlang	B-Operating_System
on	O
a	O
machine	O
with	O
16	O
GB	O
random-access	B-Architecture
memory	I-Architecture
(	O
RAM	B-Architecture
;	O
total	O
800	O
bytes/process	O
)	O
.	O
</s>
<s>
Erlang	B-Operating_System
has	O
supported	O
symmetric	B-Operating_System
multiprocessing	I-Operating_System
since	O
release	O
R11B	O
of	O
May	O
2006	O
.	O
</s>
<s>
While	O
threads	B-Operating_System
need	O
external	O
library	O
support	O
in	O
most	O
languages	O
,	O
Erlang	B-Operating_System
provides	O
language-level	O
features	O
to	O
create	O
and	O
manage	O
processes	B-Operating_System
with	O
the	O
goal	O
of	O
simplifying	O
concurrent	B-Architecture
programming	I-Architecture
.	O
</s>
<s>
Though	O
all	O
concurrency	B-Operating_System
is	O
explicit	O
in	O
Erlang	B-Operating_System
,	O
processes	B-Operating_System
communicate	O
using	O
message	B-Architecture
passing	I-Architecture
instead	O
of	O
shared	O
variables	O
,	O
which	O
removes	O
the	O
need	O
for	O
explicit	O
locks	B-Operating_System
(	O
a	O
locking	B-Operating_System
scheme	O
is	O
still	O
used	O
internally	O
by	O
the	O
VM	O
)	O
.	O
</s>
<s>
Inter-process	B-Operating_System
communication	I-Operating_System
works	O
via	O
a	O
shared-nothing	B-Operating_System
asynchronous	B-Operating_System
message	B-Architecture
passing	I-Architecture
system	O
:	O
every	O
process	O
has	O
a	O
"	O
mailbox	O
"	O
,	O
a	O
queue	B-Application
of	O
messages	O
that	O
have	O
been	O
sent	O
by	O
other	O
processes	B-Operating_System
and	O
not	O
yet	O
consumed	O
.	O
</s>
<s>
A	O
message	O
may	O
comprise	O
any	O
Erlang	B-Operating_System
structure	O
,	O
including	O
primitives	O
(	O
integers	O
,	O
floats	O
,	O
characters	O
,	O
atoms	O
)	O
,	O
tuples	O
,	O
lists	O
,	O
and	O
functions	O
.	O
</s>
<s>
The	O
code	O
example	O
below	O
shows	O
the	O
built-in	O
support	O
for	O
distributed	B-Architecture
processes	B-Operating_System
:	O
</s>
<s>
As	O
the	O
example	O
shows	O
,	O
processes	B-Operating_System
may	O
be	O
created	O
on	O
remote	O
nodes	O
,	O
and	O
communication	O
with	O
them	O
is	O
transparent	O
in	O
the	O
sense	O
that	O
communication	O
with	O
remote	O
processes	B-Operating_System
works	O
exactly	O
as	O
communication	O
with	O
local	O
processes	B-Operating_System
.	O
</s>
<s>
Concurrency	B-Operating_System
supports	O
the	O
primary	O
method	O
of	O
error-handling	O
in	O
Erlang	B-Operating_System
.	O
</s>
<s>
The	O
official	O
reference	O
implementation	O
of	O
Erlang	B-Operating_System
uses	O
BEAM	B-Application
.	O
</s>
<s>
BEAM	B-Application
is	O
included	O
in	O
the	O
official	O
distribution	O
of	O
Erlang	B-Operating_System
,	O
called	O
Erlang/OTP	B-Operating_System
.	O
</s>
<s>
BEAM	B-Application
executes	O
bytecode	O
which	O
is	O
converted	O
to	O
threaded	B-Application
code	I-Application
at	O
load	O
time	O
.	O
</s>
<s>
It	O
also	O
includes	O
a	O
native	O
code	O
compiler	O
on	O
most	O
platforms	O
,	O
developed	O
by	O
the	O
High	O
Performance	O
Erlang	B-Operating_System
Project	O
(	O
HiPE	B-Operating_System
)	O
at	O
Uppsala	O
University	O
.	O
</s>
<s>
Since	O
October	O
2001	O
the	O
HiPE	B-Operating_System
system	O
is	O
fully	O
integrated	O
in	O
Ericsson	O
's	O
Open	O
Source	O
Erlang/OTP	B-Operating_System
system	O
.	O
</s>
<s>
It	O
also	O
supports	O
interpreting	O
,	O
directly	O
from	O
source	O
code	O
via	O
abstract	B-Data_Structure
syntax	I-Data_Structure
tree	I-Data_Structure
,	O
via	O
script	O
as	O
of	O
R11B-5	O
release	O
of	O
Erlang	B-Operating_System
.	O
</s>
<s>
Erlang	B-Operating_System
supports	O
language-level	O
Dynamic	B-Architecture
Software	I-Architecture
Updating	I-Architecture
.	O
</s>
<s>
To	O
implement	O
this	O
,	O
code	O
is	O
loaded	O
and	O
managed	O
as	O
"	O
module	O
"	O
units	O
;	O
the	O
module	O
is	O
a	O
compilation	B-Language
unit	I-Language
.	O
</s>
<s>
The	O
system	O
can	O
keep	O
two	O
versions	O
of	O
a	O
module	O
in	O
memory	O
at	O
the	O
same	O
time	O
,	O
and	O
processes	B-Operating_System
can	O
concurrently	O
run	O
code	O
from	O
each	O
.	O
</s>
<s>
In	O
practice	O
,	O
systems	O
are	O
built	O
up	O
using	O
design	B-Architecture
principles	I-Architecture
from	O
the	O
Open	B-Language
Telecom	I-Language
Platform	I-Language
,	O
which	O
leads	O
to	O
more	O
code	O
upgradable	O
designs	O
.	O
</s>
<s>
Code	O
must	O
be	O
written	O
with	O
care	O
to	O
make	O
use	O
of	O
Erlang	B-Operating_System
's	O
facilities	O
.	O
</s>
<s>
In	O
1998	O
,	O
Ericsson	O
released	O
Erlang	B-Operating_System
as	O
free	B-License
and	I-License
open-source	I-License
software	I-License
to	O
ensure	O
its	O
independence	O
from	O
a	O
single	O
vendor	O
and	O
to	O
increase	O
awareness	O
of	O
the	O
language	O
.	O
</s>
<s>
Erlang	B-Operating_System
,	O
together	O
with	O
libraries	B-Library
and	O
the	O
real-time	O
distributed	B-Architecture
database	O
Mnesia	B-General_Concept
,	O
forms	O
the	O
OTP	O
collection	O
of	O
libraries	B-Library
.	O
</s>
<s>
Ericsson	O
and	O
a	O
few	O
other	O
companies	O
support	O
Erlang	B-Operating_System
commercially	O
.	O
</s>
<s>
Since	O
the	O
open	O
source	O
release	O
,	O
Erlang	B-Operating_System
has	O
been	O
used	O
by	O
several	O
firms	O
worldwide	O
,	O
including	O
Nortel	O
and	O
T-Mobile	O
.	O
</s>
<s>
Although	O
Erlang	B-Operating_System
was	O
designed	O
to	O
fill	O
a	O
niche	O
and	O
has	O
remained	O
an	O
obscure	O
language	O
for	O
most	O
of	O
its	O
existence	O
,	O
its	O
popularity	O
is	O
growing	O
due	O
to	O
demand	O
for	O
concurrent	B-Architecture
services	O
.	O
</s>
<s>
Erlang	B-Operating_System
has	O
found	O
some	O
use	O
in	O
fielding	O
massively	B-Protocol
multiplayer	I-Protocol
online	I-Protocol
role-playing	I-Protocol
game	I-Protocol
(	O
MMORPG	B-Protocol
)	O
servers	O
.	O
</s>
