<s>
Android	B-Application
Runtime	I-Application
(	O
ART	O
)	O
is	O
an	O
application	O
runtime	B-Device
environment	I-Device
used	O
by	O
the	O
Android	B-Application
operating	I-Application
system	I-Application
.	O
</s>
<s>
Replacing	O
Dalvik	B-Application
,	O
the	O
process	O
virtual	B-Architecture
machine	I-Architecture
originally	O
used	O
by	O
Android	B-Application
,	O
ART	O
performs	O
the	O
translation	B-Application
of	O
the	O
application	O
's	O
bytecode	O
into	O
native	O
instructions	O
that	O
are	O
later	O
executed	O
by	O
the	O
device	O
's	O
runtime	B-Device
environment	I-Device
.	O
</s>
<s>
Android	B-Application
2.2	I-Application
"	I-Application
Froyo	I-Application
"	I-Application
brought	O
trace-based	O
just-in-time	O
(	O
JIT	O
)	O
compilation	B-Language
into	O
Dalvik	B-Application
,	O
optimizing	O
the	O
execution	O
of	O
applications	O
by	O
continually	O
profiling	O
applications	O
each	O
time	O
they	O
run	O
and	O
dynamically	O
compiling	B-Language
frequently	O
executed	O
short	O
segments	O
of	O
their	O
bytecode	O
into	O
native	O
machine	B-Language
code	I-Language
.	O
</s>
<s>
While	O
Dalvik	B-Application
interprets	B-Application
the	O
rest	O
of	O
application	O
's	O
bytecode	O
,	O
native	B-Language
execution	I-Language
of	O
those	O
short	O
bytecode	O
segments	O
,	O
called	O
"	O
traces	O
"	O
,	O
provides	O
significant	O
performance	O
improvements	O
.	O
</s>
<s>
Unlike	O
Dalvik	B-Application
,	O
ART	O
introduces	O
the	O
use	O
of	O
ahead-of-time	B-Application
(	O
AOT	B-Application
)	O
compilation	B-Language
by	O
compiling	B-Language
entire	O
applications	O
into	O
native	O
machine	B-Language
code	I-Language
upon	O
their	O
installation	O
.	O
</s>
<s>
By	O
eliminating	O
Dalvik	B-Application
's	O
interpretation	O
and	O
trace-based	O
JIT	O
compilation	B-Language
,	O
ART	O
improves	O
the	O
overall	O
execution	O
efficiency	O
and	O
reduces	O
power	O
consumption	O
,	O
which	O
results	O
in	O
improved	O
battery	O
autonomy	O
on	O
mobile	B-Application
devices	I-Application
.	O
</s>
<s>
At	O
the	O
same	O
time	O
,	O
ART	O
brings	O
faster	O
execution	O
of	O
applications	O
,	O
improved	O
memory	B-General_Concept
allocation	I-General_Concept
and	O
garbage	B-General_Concept
collection	I-General_Concept
(	O
GC	O
)	O
mechanisms	O
,	O
new	O
applications	O
debugging	O
features	O
,	O
and	O
more	O
accurate	O
high-level	O
profiling	O
of	O
applications	O
.	O
</s>
<s>
To	O
maintain	O
backward	B-General_Concept
compatibility	I-General_Concept
,	O
ART	O
uses	O
the	O
same	O
input	O
bytecode	O
as	O
Dalvik	B-Application
,	O
supplied	O
through	O
standard	O
.dex	B-Application
files	O
as	O
part	O
of	O
APK	B-Application
files	I-Application
,	O
while	O
the	O
.odex	B-Application
files	O
are	O
replaced	O
with	O
Executable	O
and	O
Linkable	O
Format	O
(	O
ELF	O
)	O
executables	O
.	O
</s>
<s>
Once	O
an	O
application	O
is	O
compiled	B-Language
by	O
using	O
ART	O
's	O
on-device	O
utility	O
,	O
it	O
is	O
run	O
solely	O
from	O
the	O
compiled	B-Language
ELF	O
executable	O
;	O
as	O
a	O
result	O
,	O
ART	O
eliminates	O
various	O
application	O
execution	O
overheads	O
associated	O
with	O
Dalvik	B-Application
's	O
interpretation	O
and	O
trace-based	O
JIT	O
compilation	B-Language
.	O
</s>
<s>
A	O
disadvantage	O
of	O
ART	O
is	O
that	O
additional	O
time	O
is	O
required	O
for	O
compilation	B-Language
when	O
an	O
application	O
is	O
installed	O
,	O
and	O
applications	O
take	O
up	O
slightly	O
more	O
secondary	O
storage	O
(	O
usually	O
flash	B-Device
memory	I-Device
)	O
to	O
store	O
the	O
compiled	B-Language
code	O
.	O
</s>
<s>
Android	B-Application
4.4	I-Application
"	I-Application
KitKat	I-Application
"	I-Application
brought	O
a	O
technology	O
preview	O
of	O
ART	O
,	O
including	O
it	O
as	O
an	O
alternative	O
runtime	B-Device
environment	I-Device
and	O
keeping	O
Dalvik	B-Application
as	O
the	O
default	O
virtual	B-Architecture
machine	I-Architecture
.	O
</s>
<s>
In	O
the	O
subsequent	O
major	O
Android	B-Application
release	O
,	O
Android	B-Application
5.0	I-Application
"	I-Application
Lollipop	I-Application
"	I-Application
,	O
Dalvik	B-Application
was	O
entirely	O
replaced	O
by	O
ART	O
.	O
</s>
<s>
Android	B-Application
7.0	I-Application
"	I-Application
Nougat	I-Application
"	I-Application
switched	O
its	O
Java	O
Runtime	B-Device
Environment	I-Device
from	O
the	O
discontinued	O
Apache	B-Application
Harmony	I-Application
to	O
OpenJDK	B-Language
,	O
introducing	O
a	O
JIT	O
compiler	B-Language
with	O
code	O
profiling	O
to	O
ART	O
,	O
which	O
lets	O
it	O
constantly	O
improve	O
the	O
performance	O
of	O
Android	B-Application
apps	O
as	O
they	O
run	O
.	O
</s>
<s>
The	O
JIT	O
compiler	B-Language
complements	O
ART	O
's	O
current	O
ahead-of-time	B-Application
compiler	I-Application
and	O
helps	O
improve	O
runtime	O
performance	O
,	O
and	O
save	O
storage	O
space	O
by	O
only	O
compiling	B-Language
some	O
parts	O
of	O
the	O
apps	O
.	O
</s>
<s>
Android	B-Application
9	I-Application
"	I-Application
Pie	I-Application
"	I-Application
reduced	O
the	O
amount	O
of	O
storage	O
used	O
by	O
APKs	B-Application
by	O
using	O
compressed	O
bytecode	O
files	O
,	O
and	O
profiler	O
data	O
can	O
be	O
uploaded	O
to	O
Google	B-Application
Play	O
servers	O
to	O
be	O
bundled	O
with	O
apps	O
when	O
downloaded	O
by	O
users	O
with	O
a	O
similar	O
device	O
.	O
</s>
<s>
Android	B-Application
13	I-Application
ART	O
will	O
be	O
updated	O
with	O
a	O
new	O
garbage	B-General_Concept
collector	I-General_Concept
(	O
GC	O
)	O
utilizing	O
the	O
Linux	B-Operating_System
userfaultfd	O
system	B-Operating_System
call	I-Operating_System
.	O
</s>
<s>
It	O
reduces	O
memory	O
pressure	O
,	O
compiled	B-Language
code	O
size	O
,	O
jank	O
and	O
prevents	O
the	O
risk	O
of	O
killing	O
apps	O
because	O
of	O
low	O
memory	O
during	O
GC	O
.	O
</s>
<s>
Because	O
of	O
the	O
Mainline	O
project	O
,	O
Android	B-Application
12	O
ART	O
will	O
also	O
be	O
updated	O
.	O
</s>
