<s>
The	O
EFI	O
(	O
Extensible	B-Architecture
Firmware	I-Architecture
Interface	I-Architecture
)	O
system	B-Application
partition	I-Application
or	O
ESP	O
is	O
a	O
partition	B-Application
on	O
a	O
data	B-General_Concept
storage	I-General_Concept
device	I-General_Concept
(	O
usually	O
a	O
hard	B-Device
disk	I-Device
drive	I-Device
or	O
solid-state	B-Device
drive	I-Device
)	O
that	O
is	O
used	O
by	O
computers	O
having	O
the	O
Unified	B-Architecture
Extensible	I-Architecture
Firmware	I-Architecture
Interface	I-Architecture
(	O
UEFI	B-Architecture
)	O
.	O
</s>
<s>
When	O
a	O
computer	O
is	O
booted	B-Operating_System
,	O
UEFI	B-Architecture
firmware	I-Architecture
loads	O
files	O
stored	O
on	O
the	O
ESP	O
to	O
start	O
installing	O
operating	B-General_Concept
systems	I-General_Concept
and	O
various	O
utilities	O
.	O
</s>
<s>
An	O
ESP	O
contains	O
the	O
boot	B-Application
loaders	I-Application
or	O
kernel	B-Operating_System
images	I-Operating_System
for	O
all	O
installed	O
operating	B-General_Concept
systems	I-General_Concept
(	O
which	O
are	O
contained	O
in	O
other	O
partitions	B-Application
)	O
,	O
device	B-Application
driver	I-Application
files	O
for	O
hardware	O
devices	O
present	O
in	O
a	O
computer	O
and	O
used	O
by	O
the	O
firmware	B-Application
at	O
boot	B-Operating_System
time	I-Operating_System
,	O
system	O
utility	O
programs	O
that	O
are	O
intended	O
to	O
be	O
run	O
before	O
an	O
operating	B-General_Concept
system	I-General_Concept
is	O
booted	B-Operating_System
,	O
and	O
data	O
files	O
such	O
as	O
error	O
logs	O
.	O
</s>
<s>
The	O
EFI	B-Device
system	I-Device
partition	I-Device
is	O
formatted	O
with	O
a	O
file	B-Application
system	I-Application
whose	O
specification	O
is	O
based	O
on	O
the	O
FAT	B-Application
file	I-Application
system	I-Application
and	O
maintained	O
as	O
part	O
of	O
the	O
UEFI	B-Architecture
specification	O
;	O
therefore	O
,	O
the	O
file	B-Application
system	I-Application
specification	O
is	O
independent	O
from	O
the	O
original	O
FAT	O
specification	O
.	O
</s>
<s>
The	O
globally	O
unique	O
identifier	O
(	O
GUID	O
)	O
for	O
the	O
EFI	B-Device
system	I-Device
partition	I-Device
in	O
the	O
GUID	B-Application
Partition	I-Application
Table	I-Application
(	O
GPT	O
)	O
scheme	O
is	O
,	O
while	O
its	O
ID	O
in	O
the	O
master	B-Device
boot	I-Device
record	I-Device
(	O
MBR	O
)	O
partition-table	O
scheme	O
is	O
.	O
</s>
<s>
Both	O
GPT	O
-	O
and	O
MBR-partitioned	O
disks	O
can	O
contain	O
an	O
EFI	B-Device
system	I-Device
partition	I-Device
,	O
as	O
UEFI	B-Architecture
firmware	I-Architecture
is	O
required	O
to	O
support	O
both	O
partitioning	B-Application
schemes	O
.	O
</s>
<s>
Also	O
,	O
El	B-Device
Torito	I-Device
bootable	B-Operating_System
format	O
for	O
CD-ROMs	B-Device
and	O
DVDs	O
is	O
supported	O
.	O
</s>
<s>
UEFI	B-Architecture
provides	O
backward	B-General_Concept
compatibility	I-General_Concept
with	O
legacy	O
systems	O
by	O
reserving	O
the	O
first	O
block	O
(	O
sector	O
)	O
of	O
the	O
partition	B-Application
for	O
compatibility	O
code	O
,	O
effectively	O
creating	O
a	O
legacy	O
boot	B-Device
sector	I-Device
.	O
</s>
<s>
On	O
legacy	O
BIOS-based	O
systems	O
,	O
the	O
first	O
sector	O
of	O
a	O
partition	B-Application
is	O
loaded	O
into	O
memory	O
,	O
and	O
execution	O
is	O
transferred	O
to	O
this	O
code	O
.	O
</s>
<s>
UEFI	B-Architecture
firmware	I-Architecture
does	O
not	O
execute	O
the	O
code	O
in	O
the	O
MBR	O
,	O
except	O
when	O
booting	B-Operating_System
in	O
legacy	B-Operating_System
BIOS	I-Operating_System
mode	O
through	O
the	O
Compatibility	O
Support	O
Module	O
(	O
CSM	O
)	O
.	O
</s>
<s>
The	O
UEFI	B-Architecture
specification	O
requires	O
MBR	O
partition	B-Application
tables	O
to	O
be	O
fully	O
supported	O
.	O
</s>
<s>
However	O
,	O
some	O
UEFI	B-Architecture
implementations	O
immediately	O
switch	O
to	O
the	O
BIOS-based	O
CSM	O
booting	B-Operating_System
upon	O
detecting	O
certain	O
types	O
of	O
partition	B-Application
table	O
on	O
the	O
boot	B-Operating_System
disk	O
,	O
effectively	O
preventing	O
UEFI	B-Architecture
booting	B-Operating_System
to	O
be	O
performed	O
from	O
EFI	B-Device
system	I-Device
partitions	I-Device
contained	O
on	O
MBR-partitioned	O
disks	O
.	O
</s>
<s>
UEFI	B-Architecture
firmware	I-Architecture
supports	O
booting	B-Operating_System
from	O
removable	O
storage	O
devices	O
such	O
as	O
USB	O
flash	O
drives	O
.	O
</s>
<s>
For	O
that	O
purpose	O
,	O
a	O
removable	O
device	O
is	O
formatted	O
with	O
a	O
FAT12	B-Application
,	O
FAT16	B-Application
or	O
FAT32	B-Application
file	B-Application
system	I-Application
,	O
while	O
a	O
boot	B-Application
loader	I-Application
needs	O
to	O
be	O
stored	O
according	O
to	O
the	O
standard	O
ESP	O
file	O
hierarchy	O
,	O
or	O
by	O
providing	O
a	O
complete	O
path	O
of	O
a	O
boot	B-Application
loader	I-Application
to	O
the	O
system	O
's	O
boot	B-Application
manager	I-Application
.	O
</s>
<s>
On	O
the	O
other	O
hand	O
,	O
FAT32	B-Application
is	O
always	O
expected	O
on	O
fixed	B-Device
drives	I-Device
.	O
</s>
<s>
GRUB	B-Application
2	I-Application
and	O
elilo	O
serve	O
as	O
conventional	O
,	O
full-fledged	O
standalone	O
UEFI	B-Architecture
boot	B-Application
loaders	I-Application
for	O
Linux	B-Operating_System
.	O
</s>
<s>
Once	O
loaded	O
by	O
a	O
UEFI	B-Architecture
firmware	I-Architecture
,	O
they	O
both	O
can	O
access	O
and	O
boot	B-Operating_System
kernel	B-Operating_System
images	I-Operating_System
from	O
all	O
devices	O
,	O
partitions	B-Application
and	O
file	B-Application
systems	I-Application
they	O
support	O
,	O
without	O
being	O
limited	O
to	O
the	O
EFI	B-Device
system	I-Device
partition	I-Device
.	O
</s>
<s>
EFI	O
Boot	B-Operating_System
Stub	O
makes	O
it	O
possible	O
to	O
boot	B-Operating_System
a	O
Linux	B-Operating_System
kernel	I-Operating_System
image	O
without	O
the	O
use	O
of	O
a	O
conventional	O
UEFI	B-Architecture
boot	B-Application
loader	I-Application
.	O
</s>
<s>
By	O
masquerading	O
as	O
a	O
PE/COFF	O
image	O
and	O
appearing	O
to	O
the	O
firmware	B-Application
as	O
a	O
UEFI	B-Architecture
application	O
,	O
an	O
x86	O
kernel	B-Operating_System
image	I-Operating_System
with	O
EFI	O
Boot	B-Operating_System
Stub	O
enabled	O
can	O
be	O
directly	O
loaded	O
and	O
executed	O
by	O
a	O
UEFI	B-Architecture
firmware	I-Architecture
.	O
</s>
<s>
Such	O
kernel	B-Operating_System
images	I-Operating_System
can	O
still	O
be	O
loaded	O
and	O
run	O
by	O
BIOS-based	O
boot	B-Application
loaders	I-Application
;	O
thus	O
,	O
EFI	O
Boot	B-Operating_System
Stub	O
allows	O
a	O
single	O
kernel	B-Operating_System
image	I-Operating_System
to	O
work	O
in	O
any	O
boot	B-Operating_System
environment	O
.	O
</s>
<s>
Linux	B-Operating_System
kernel	I-Operating_System
's	O
support	O
for	O
the	O
EFI	O
Boot	B-Operating_System
Stub	O
is	O
enabled	O
by	O
turning	O
on	O
option	O
CONFIG_EFI_STUB	O
(	O
EFI	O
stub	O
support	O
)	O
during	O
the	O
kernel	B-Operating_System
configuration	O
.	O
</s>
<s>
It	O
was	O
merged	O
into	O
version	O
3.3	O
of	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
mainline	O
,	O
released	O
on	O
March	O
18	O
,	O
2012	O
.	O
</s>
<s>
Gummiboot	B-Application
(	O
a.k.a.	O
</s>
<s>
systemd-boot	B-Application
)	O
is	O
a	O
simple	O
UEFI	B-Architecture
boot	B-Application
manager	I-Application
that	O
loads	O
and	O
runs	O
configured	O
UEFI	B-Architecture
images	O
,	O
accessing	O
only	O
the	O
EFI	B-Device
system	I-Device
partition	I-Device
.	O
</s>
<s>
Configuration	O
file	O
fragments	O
,	O
kernel	B-Operating_System
images	I-Operating_System
and	O
initrd	B-Application
images	O
are	O
required	O
to	O
reside	O
on	O
the	O
EFI	B-Device
system	I-Device
partition	I-Device
,	O
as	O
Gummiboot	B-Application
does	O
not	O
provide	O
support	O
for	O
accessing	O
files	O
on	O
other	O
partitions	B-Application
or	O
file	B-Application
systems	I-Application
.	O
</s>
<s>
Linux	B-Operating_System
kernels	I-Operating_System
need	O
to	O
be	O
built	O
with	O
CONFIG_EFI_STUB	O
enabled	O
so	O
they	O
can	O
be	O
directly	O
executed	O
as	O
UEFI	B-Architecture
images	O
.	O
</s>
<s>
The	O
mount	O
point	O
for	O
the	O
EFI	B-Device
system	I-Device
partition	I-Device
is	O
usually	O
/boot/efi	O
,	O
where	O
its	O
content	O
is	O
accessible	O
after	O
Linux	B-Operating_System
is	O
booted	B-Operating_System
.	O
</s>
<s>
On	O
macOS	B-Application
computers	O
based	O
on	O
the	O
x64	B-Device
hardware	O
architecture	O
,	O
the	O
EFI	B-Device
system	I-Device
partition	I-Device
is	O
initially	O
left	O
blank	O
and	O
unused	O
for	O
booting	B-Operating_System
.	O
</s>
<s>
However	O
,	O
the	O
EFI	B-Device
system	I-Device
partition	I-Device
is	O
used	O
as	O
a	O
staging	O
area	O
for	O
firmware	B-Application
updates	O
.	O
</s>
<s>
The	O
logic	O
usually	O
goes	O
as	O
follows	O
:	O
the	O
EFI	O
first	O
looks	O
for	O
a	O
bootloader	B-Application
in	O
ESP	O
,	O
and	O
if	O
there	O
is	O
none	O
it	O
will	O
continue	O
to	O
the	O
macOS	B-Application
file	B-Application
system	I-Application
.	O
</s>
<s>
The	O
pre-UEFI	O
Apple	B-Device
–	I-Device
Intel	I-Device
architecture	I-Device
(	O
mactel	B-Device
)	O
EFI	O
subsystem	O
used	O
to	O
require	O
the	O
EFI	B-Device
system	I-Device
partition	I-Device
to	O
be	O
formatted	O
in	O
HFS+	B-Application
.	O
</s>
<s>
Any	O
third-party	O
bootloader	B-Application
also	O
needs	O
to	O
be	O
"	O
blessed	O
"	O
by	O
a	O
special	O
ioctl	B-Operating_System
command	O
before	O
becoming	O
bootable	B-Operating_System
by	O
the	O
firmware	B-Application
,	O
a	O
relic	O
of	O
the	O
system	B-Operating_System
folder	I-Operating_System
blessing	O
from	O
classic	B-Application
Mac	I-Application
OS	I-Application
.	O
</s>
<s>
There	O
is	O
otherwise	O
no	O
limitations	O
to	O
what	O
kinds	O
of	O
EFI	O
operating	B-General_Concept
system	I-General_Concept
or	O
bootloader	B-Application
a	O
mactel	B-Device
machine	O
can	O
run	O
.	O
</s>
<s>
On	O
Windows	B-Application
XP	I-Application
64-Bit	O
Edition	O
and	O
later	O
,	O
access	O
to	O
the	O
EFI	B-Device
system	I-Device
partition	I-Device
is	O
obtained	O
by	O
running	O
the	O
command	O
.	O
</s>
<s>
The	O
Windows	O
boot	B-Application
manager	I-Application
is	O
located	O
at	O
the	O
subfolder	O
of	O
the	O
EFI	B-Device
system	I-Device
partition	I-Device
.	O
</s>
