<s>
In	O
computer	B-General_Concept
programming	I-General_Concept
,	O
a	O
runtime	B-Library
library	I-Library
is	O
a	O
set	O
of	O
low-level	O
routines	O
used	O
by	O
a	O
compiler	B-Language
to	O
invoke	O
some	O
of	O
the	O
behaviors	O
of	O
a	O
runtime	B-Device
environment	I-Device
,	O
by	O
inserting	O
calls	O
to	O
the	O
runtime	B-Library
library	I-Library
into	O
compiled	B-Language
executable	O
binary	O
.	O
</s>
<s>
The	O
runtime	B-Device
environment	I-Device
implements	O
the	O
execution	B-Device
model	I-Device
,	O
built-in	O
functions	O
,	O
and	O
other	O
fundamental	O
behaviors	O
of	O
a	O
programming	O
language	O
.	O
</s>
<s>
During	O
execution	O
(	O
run	B-Library
time	I-Library
)	O
of	O
that	O
computer	B-Application
program	I-Application
,	O
execution	O
of	O
those	O
calls	O
to	O
the	O
runtime	B-Library
library	I-Library
cause	O
communication	O
between	O
the	O
executable	O
binary	O
and	O
the	O
runtime	B-Device
environment	I-Device
.	O
</s>
<s>
A	O
runtime	B-Library
library	I-Library
often	O
includes	O
built-in	O
functions	O
for	O
memory	O
management	O
or	O
exception	B-General_Concept
handling	I-General_Concept
.	O
</s>
<s>
Therefore	O
,	O
a	O
runtime	B-Library
library	I-Library
is	O
always	O
specific	O
to	O
the	O
platform	O
and	O
compiler	B-Language
.	O
</s>
<s>
The	O
runtime	B-Library
library	I-Library
may	O
implement	O
a	O
portion	O
of	O
the	O
runtime	B-Device
environment	I-Device
's	O
behavior	O
,	O
but	O
if	O
one	O
reads	O
the	O
code	O
of	O
the	O
calls	O
available	O
,	O
they	O
are	O
typically	O
only	O
thin	O
wrappers	O
that	O
simply	O
package	O
information	O
,	O
and	O
send	O
it	O
to	O
the	O
runtime	B-Device
environment	I-Device
or	O
operating	O
system	O
.	O
</s>
<s>
However	O
,	O
sometimes	O
the	O
term	O
runtime	B-Library
library	I-Library
is	O
meant	O
to	O
include	O
the	O
code	O
of	O
the	O
runtime	B-Device
environment	I-Device
itself	O
,	O
even	O
though	O
much	O
of	O
that	O
code	O
cannot	O
be	O
directly	O
reached	O
via	O
a	O
library	O
call	O
.	O
</s>
<s>
For	O
example	O
,	O
some	O
language	O
features	O
that	O
can	O
be	O
performed	O
only	O
(	O
or	O
are	O
more	O
efficient	O
or	O
accurate	O
)	O
at	B-Library
runtime	I-Library
are	O
implemented	O
in	O
the	O
runtime	B-Device
environment	I-Device
and	O
may	O
be	O
invoked	O
via	O
the	O
runtime	B-Library
library	I-Library
API	O
,	O
e.g.	O
</s>
<s>
some	O
logic	O
errors	O
,	O
array	B-Data_Structure
bounds	I-Data_Structure
checking	I-Data_Structure
,	O
dynamic	O
type	O
checking	O
,	O
exception	B-General_Concept
handling	I-General_Concept
,	O
and	O
possibly	O
debugging	O
functionality	O
.	O
</s>
<s>
For	O
this	O
reason	O
,	O
some	O
programming	O
bugs	O
are	O
not	O
discovered	O
until	O
the	O
program	O
is	O
tested	O
in	O
a	O
"	O
live	O
"	O
environment	O
with	O
real	O
data	O
,	O
despite	O
sophisticated	O
compile-time	O
checking	O
and	O
testing	O
performed	O
during	O
development	O
.	O
</s>
<s>
As	O
another	O
example	O
,	O
a	O
runtime	B-Library
library	I-Library
may	O
contain	O
code	O
of	O
built-in	O
low-level	O
operations	O
too	O
complicated	O
for	O
their	O
inlining	O
during	O
compilation	B-Language
,	O
such	O
as	O
implementations	O
of	O
arithmetic	O
operations	O
not	O
directly	O
supported	O
by	O
the	O
targeted	O
CPU	O
,	O
or	O
various	O
miscellaneous	O
compiler-specific	O
operations	O
and	O
directives	O
.	O
</s>
<s>
The	O
concept	O
of	O
a	O
runtime	B-Library
library	I-Library
should	O
not	O
be	O
confused	O
with	O
an	O
ordinary	O
program	B-Library
library	I-Library
like	O
that	O
created	O
by	O
an	O
application	O
programmer	O
or	O
delivered	O
by	O
a	O
third	O
party	O
,	O
nor	O
with	O
a	O
dynamic	B-Application
library	I-Application
,	O
meaning	O
a	O
program	B-Library
library	I-Library
linked	O
at	O
run	B-Library
time	I-Library
.	O
</s>
<s>
For	O
example	O
,	O
the	O
C	B-Language
programming	I-Language
language	I-Language
requires	O
only	O
a	O
minimal	O
runtime	B-Library
library	I-Library
(	O
commonly	O
called	O
crt0	B-Language
)	O
,	O
but	O
defines	O
a	O
large	O
standard	O
library	O
(	O
called	O
C	B-Language
standard	I-Language
library	I-Language
)	O
that	O
has	O
to	O
be	O
provided	O
by	O
each	O
implementation	O
.	O
</s>
