<s>
The	O
booting	B-Application
process	I-Application
of	I-Application
Android	I-Application
devices	I-Application
starts	O
at	O
the	O
power-on	O
of	O
the	O
SoC	O
(	O
system	B-Architecture
on	I-Architecture
a	I-Architecture
chip	I-Architecture
)	O
and	O
ends	O
at	O
the	O
visibility	O
of	O
the	O
home	B-Operating_System
screen	I-Operating_System
,	O
or	O
special	O
modes	O
like	O
recovery	B-Application
and	O
fastboot	B-Application
.	O
</s>
<s>
The	O
boot	B-Operating_System
process	I-Operating_System
of	O
devices	O
that	O
run	O
Android	B-Application
is	O
influenced	O
by	O
the	O
firmware	O
design	O
of	O
the	O
SoC	O
manufacturers	O
.	O
</s>
<s>
As	O
of	O
2018	O
,	O
90%	O
of	O
the	O
SoCs	O
of	O
the	O
Android	B-Application
market	O
are	O
supplied	O
by	O
either	O
Qualcomm	O
,	O
Samsung	O
or	O
MediaTek	B-Architecture
.	O
</s>
<s>
Other	O
vendors	O
include	O
Rockchip	B-Architecture
,	O
Marvell	O
,	O
Nvidia	O
and	O
previously	O
Texas	O
Instruments	O
.	O
</s>
<s>
Verified	O
boot	B-Operating_System
was	O
introduced	O
with	O
Android	B-Application
KitKat	I-Application
.	O
</s>
<s>
The	O
Primary	O
Bootloader	O
(	O
PBL	O
)	O
,	O
which	O
is	O
stored	O
in	O
the	O
Boot	B-General_Concept
ROM	I-General_Concept
is	O
the	O
first	O
stage	O
of	O
the	O
boot	B-Operating_System
process	I-Operating_System
.	O
</s>
<s>
On	O
Samsung	O
smartphones	O
,	O
the	O
Samsung	O
Secure	O
Boot	B-Operating_System
Key	O
(	O
SSBK	O
)	O
is	O
used	O
by	O
the	O
boot	B-General_Concept
ROM	I-General_Concept
to	O
verify	O
the	O
next	O
stages	O
.	O
</s>
<s>
Because	O
the	O
space	O
in	O
the	O
boot	B-General_Concept
ROM	I-General_Concept
is	O
limited	O
,	O
a	O
secondary	O
bootloader	O
on	O
the	O
eMMC	O
or	O
eUFS	B-Device
is	O
used	O
.	O
</s>
<s>
The	O
SBL	O
is	O
now	O
called	O
XBL	O
by	O
Qualcomm	O
and	O
uses	O
UEFI	B-Architecture
to	O
be	O
cross	O
compatible	O
for	O
booting	B-Operating_System
operating	O
systems	O
other	O
than	O
Android	B-Application
in	O
the	O
second	O
stage	O
.	O
</s>
<s>
Qualcomm	O
uses	O
Little	O
Kernel	O
,	O
MediaTek	B-Architecture
uses	O
Das	B-Language
U-Boot	I-Language
.	O
</s>
<s>
Little	O
Kernel	O
is	O
a	O
microkernel	B-Operating_System
for	O
embedded	B-Architecture
devices	I-Architecture
,	O
which	O
has	O
been	O
modified	O
by	O
Qualcomm	O
to	O
use	O
it	O
as	O
an	O
Android	B-Application
bootloader	O
.	O
</s>
<s>
The	O
Android	B-Application
Bootloader	O
(	O
Aboot	O
)	O
,	O
which	O
implements	O
the	O
fastboot	B-Application
interface	O
(	O
which	O
is	O
absent	O
in	O
Samsung	O
devices	O
)	O
.	O
</s>
<s>
Aboot	O
verifies	O
the	O
authenticity	O
of	O
the	O
boot	B-Operating_System
and	O
recovery	B-Application
partitions	B-Application
.	O
</s>
<s>
By	O
pressing	O
a	O
specific	O
key	O
combination	O
,	O
devices	O
can	O
also	O
boot	B-Operating_System
in	O
recovery	B-Application
mode	I-Application
.	O
</s>
<s>
The	O
initramfs	O
is	O
a	O
gzip'ed	B-Application
cpio	B-Application
archive	O
that	O
contains	O
a	O
small	O
root	O
file	O
system	O
.	O
</s>
<s>
The	O
Android	B-Application
kernel	O
is	O
a	O
modified	O
version	O
of	O
the	O
Linux	O
kernel	O
.	O
</s>
<s>
Init	O
does	O
mount	O
the	O
partitions	B-Application
.	O
</s>
<s>
dm-verity	O
verifies	O
the	O
integrity	O
of	O
the	O
partitions	B-Application
that	O
are	O
specified	O
in	O
the	O
fstab	O
file	O
.	O
</s>
<s>
dm-verity	O
is	O
a	O
Linux	O
kernel	O
module	O
that	O
was	O
introduced	O
by	O
Google	O
in	O
Android	B-Application
since	O
version	O
4.4	O
.	O
</s>
<s>
Zygote	O
is	O
spawned	O
by	O
the	O
init	O
process	O
,	O
which	O
is	O
responsible	O
for	O
starting	O
Android	B-Application
applications	I-Application
and	O
service	O
processes	O
.	O
</s>
<s>
When	O
a	O
new	O
applications	O
starts	O
,	O
a	O
command	O
is	O
sent	O
to	O
Zygote	O
which	O
executes	O
a	O
fork( )	O
system	O
call	O
.	O
</s>
<s>
The	O
Android	B-Application
system	I-Application
is	O
divided	O
across	O
different	O
partitions	B-Application
.	O
</s>
<s>
The	O
Qualcomm	O
platform	O
makes	O
use	O
of	O
the	O
GUID	B-Application
partition	I-Application
table	I-Application
.	O
</s>
<s>
Although	O
this	O
specification	O
is	O
part	O
of	O
the	O
UEFI	B-Architecture
specification	O
,	O
it	O
does	O
not	O
depend	O
on	O
UEFI	B-Architecture
.	O
</s>
