<s>
Operating	B-General_Concept
systems	I-General_Concept
based	O
on	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
are	O
used	O
in	O
embedded	B-Architecture
systems	I-Architecture
such	O
as	O
consumer	O
electronics	O
(	O
eg	O
.	O
</s>
<s>
set-top	O
boxes	O
,	O
smart	B-Device
TVs	I-Device
and	O
personal	B-Application
video	I-Application
recorders	I-Application
(	O
PVRs	O
)	O
)	O
,	O
in-vehicle	O
infotainment	O
(	O
IVI	O
)	O
,	O
networking	B-Architecture
equipment	O
(	O
such	O
as	O
routers	B-Protocol
,	O
switches	B-Protocol
,	O
wireless	B-Device
access	I-Device
points	I-Device
(	O
WAPs	O
)	O
or	O
wireless	B-Device
routers	I-Device
)	O
,	O
machine	O
control	O
,	O
industrial	O
automation	O
,	O
navigation	O
equipment	O
,	O
spacecraft	O
flight	O
software	O
,	O
and	O
medical	O
instruments	O
in	O
general	O
.	O
</s>
<s>
Because	O
of	O
their	O
versatility	B-Application
,	O
operating	B-General_Concept
systems	I-General_Concept
based	O
on	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
can	O
be	O
also	O
found	O
in	B-Application
mobile	I-Application
devices	I-Application
that	O
are	O
actually	O
touchscreen-based	O
embedded	B-Architecture
devices	I-Architecture
,	O
such	O
as	O
smartphones	B-Application
and	O
tablets	B-Device
,	O
together	O
with	O
personal	B-Application
digital	I-Application
assistants	I-Application
(	O
PDAs	B-Application
)	O
and	O
portable	O
media	O
players	O
that	O
also	O
include	O
a	O
touchscreen	B-Device
.	O
</s>
<s>
This	O
is	O
a	O
challenge	O
for	O
most	O
learners	O
because	O
their	O
computer	O
experience	O
is	O
mainly	O
based	O
on	O
GUI	B-Application
(	O
Graphical	B-Application
user	I-Application
interface	I-Application
)	O
based	O
interaction	O
with	O
the	O
machine	O
and	O
high-level	O
programming	O
on	O
the	O
one	O
hand	O
and	O
low-level	O
programming	O
of	O
small	O
microcontrollers	B-Architecture
(	O
MCU	O
)	O
on	O
the	O
other	O
hand	O
while	O
the	O
concept	O
of	O
command	B-Application
line	I-Application
interfaces	I-Application
is	O
widely	O
unknown	O
.	O
</s>
<s>
The	O
Linux	B-Operating_System
kernel	I-Operating_System
has	O
been	O
ported	O
to	O
a	O
variety	O
of	O
CPUs	B-General_Concept
which	O
are	O
not	O
only	O
primarily	O
used	O
as	O
the	O
processor	O
of	O
a	O
desktop	O
or	O
server	O
computer	O
,	O
but	O
also	O
ARC	B-Application
,	O
ARM	B-Architecture
,	O
AVR32	B-Device
,	O
ETRAX	B-Device
CRIS	I-Device
,	O
FR-V	B-General_Concept
,	O
H8300	B-Device
,	O
IP7000	O
,	O
m68k	B-Device
,	O
MIPS	B-Device
,	O
mn10300	O
,	O
PowerPC	B-Architecture
,	O
SuperH	O
,	O
and	O
Xtensa	O
processors	O
.	O
</s>
<s>
Linux	B-Operating_System
is	O
also	O
used	O
as	O
an	O
alternative	O
to	O
using	O
a	O
proprietary	B-Application
operating	B-General_Concept
system	I-General_Concept
and	O
its	O
associated	O
toolchain	B-General_Concept
.	O
</s>
<s>
The	O
Embeddable	B-Application
Linux	I-Application
Kernel	I-Application
Subset	I-Application
is	O
a	O
Linux	B-Application
distribution	I-Application
that	O
fits	O
on	O
a	O
floppy	B-Device
disk	I-Device
for	O
outdated	O
or	O
low	B-Device
resource	I-Device
hardware	B-Architecture
.	O
</s>
<s>
Due	O
to	O
its	O
low	O
cost	O
(	O
freely	O
available	O
source	O
code	O
)	O
and	O
ease	O
of	O
customization	O
,	O
Linux	B-Operating_System
has	O
been	O
shipped	O
in	O
many	O
consumer	O
devices	O
.	O
</s>
<s>
Devices	O
covering	O
PDAs	B-Application
(	O
like	O
the	O
Sharp	B-Operating_System
Zaurus	I-Operating_System
family	O
)	O
,	O
TomTom	O
GPS	O
navigation	O
devices	O
,	O
residential	B-Application
gateways	I-Application
like	O
the	O
Linksys	B-Application
WRT54G	I-Application
series	I-Application
or	O
smartphones	B-Application
such	O
as	O
the	O
Motorola	O
exz	O
series	O
,	O
Openmoko	B-Application
handsets	O
,	O
devices	O
running	O
Sailfish	B-Operating_System
OS	I-Operating_System
developed	O
by	O
Jolla	B-Operating_System
like	O
Jolla	B-Operating_System
C	O
and	O
Intex	O
Aqua	O
Fish	O
and	O
the	O
Nokia	B-Application
N900	I-Application
and	O
Nokia	B-Operating_System
N9	I-Operating_System
.	O
</s>
<s>
Android	B-Application
,	O
a	O
Linux-kernel-based	O
operating	B-General_Concept
system	I-General_Concept
acquired	O
and	O
extended	O
by	O
Google	B-Application
and	O
introduced	O
in	O
2008	O
,	O
has	O
become	O
a	O
highly	O
competitive	O
platform	O
for	O
smartphones	B-Application
and	O
tablets	B-Device
.	O
</s>
<s>
In	O
July	O
2012	O
,	O
Android	B-Application
's	O
smartphone	B-Application
market	O
share	O
in	O
the	O
United	O
States	O
was	O
at	O
52%	O
,	O
reaching	O
82%	O
worldwide	O
in	O
Q2	O
2015	O
.	O
</s>
<s>
With	O
the	O
availability	O
of	O
consumer	O
embedded	B-Architecture
devices	I-Architecture
,	O
communities	O
of	O
users	O
and	O
developers	O
were	O
formed	O
around	O
these	O
devices	O
:	O
replacement	O
or	O
enhancements	O
of	O
the	O
Linux	B-Application
distribution	I-Application
shipped	O
on	O
the	O
device	O
has	O
often	O
been	O
made	O
possible	O
thanks	O
to	O
availability	O
of	O
the	O
source	O
code	O
and	O
to	O
the	O
communities	O
surrounding	O
the	O
devices	O
.	O
</s>
<s>
Due	O
to	O
the	O
high	O
number	O
of	O
devices	O
,	O
standardized	O
build	O
systems	O
have	O
appeared	O
,	O
including	O
Yocto	B-Application
,	O
OpenEmbedded	B-Application
,	O
Buildroot	B-Application
,	O
OpenWrt	B-Application
,	O
and	O
LTIB	B-Application
.	O
</s>
<s>
The	O
advantages	O
of	O
embedded	B-Application
Linux	I-Application
over	O
proprietary	B-Application
embedded	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
include	O
multiple	O
suppliers	O
for	O
software	O
,	O
development	O
and	O
support	O
;	O
no	O
royalties	O
or	O
licensing	O
fees	O
;	O
a	O
stable	O
kernel	B-Operating_System
;	O
the	O
ability	O
to	O
read	O
,	O
modify	O
and	O
redistribute	O
the	O
source	O
code	O
.	O
</s>
<s>
The	O
technical	O
disadvantages	O
include	O
a	O
comparatively	O
large	O
memory	O
footprint	O
(	O
kernel	B-Operating_System
and	O
root	O
filesystem	O
)	O
;	O
complexities	O
of	O
user	O
mode	O
and	O
kernel	B-Operating_System
mode	O
memory	O
access	O
,	O
and	O
a	O
complex	O
device	B-Application
drivers	I-Application
framework	O
.	O
</s>
<s>
Not	O
every	O
embedded	B-Application
Linux	I-Application
distribution	O
is	O
required	O
to	O
or	O
meets	O
real-time	B-General_Concept
requirements	O
.	O
</s>
<s>
This	O
is	O
particular	O
relevant	O
for	O
safety	B-Application
critical	I-Application
applications	O
and	O
systems	O
.	O
</s>
<s>
Projects	O
to	O
develop	O
real-time	B-General_Concept
and	O
safety-critical	B-Application
support	O
are	O
Real-Time	B-General_Concept
Linux	B-Operating_System
(	O
PREEMPT_RT	O
)	O
and	O
ELISA	O
(	O
under	O
Linux	B-Operating_System
Foundation	I-Operating_System
)	O
.	O
</s>
<s>
Real	B-Application
Time	I-Application
Linux	I-Application
project	O
aims	O
mainlining	O
the	O
PREEMPT_RT-version	O
.	O
</s>
<s>
In	O
order	O
for	O
the	O
electronic	O
system	O
to	O
run	O
fully-fledged	O
Linux	B-Operating_System
OS	O
and	O
have	O
multitasking	B-Operating_System
it	O
has	O
to	O
have	O
enough	O
operative	O
memory	O
(	O
or	O
replacing	O
such	O
)	O
and	O
memory	B-General_Concept
management	I-General_Concept
unit	I-General_Concept
implementing	O
virtual	B-General_Concept
addressing	I-General_Concept
to	O
ensure	O
compatibility	O
with	O
software	O
running	O
on	O
Linux	B-Operating_System
.	O
</s>
