<s>
A	O
boot	B-Operating_System
flag	I-Operating_System
is	O
a	O
1-byte	O
value	O
in	O
a	O
non-extended	O
partition	O
record	O
,	O
within	O
a	O
master	B-Device
boot	I-Device
record	I-Device
.	O
</s>
<s>
It	O
appears	O
at	O
the	O
beginning	O
of	O
a	O
partition	B-Application
record	O
,	O
as	O
the	O
value	O
0x80	O
.	O
</s>
<s>
A	O
value	O
of	O
0x00	O
indicates	O
the	O
partition	B-Application
does	O
not	O
have	O
the	O
boot	B-Operating_System
flag	I-Operating_System
set	O
.	O
</s>
<s>
Its	O
primary	O
function	O
is	O
to	O
indicate	O
to	O
a	O
MS-DOS/MS	O
Windows-type	O
boot	B-Application
loader	I-Application
which	O
partition	B-Application
to	O
boot	O
.	O
</s>
<s>
In	O
some	O
cases	O
it	O
is	O
used	O
by	O
Windows	O
XP/2000	O
to	O
assign	O
the	O
active	B-Operating_System
partition	I-Operating_System
the	O
letter	O
"	O
C	O
:	O
"	O
.	O
</s>
<s>
The	O
active	B-Operating_System
partition	I-Operating_System
is	O
the	O
partition	B-Application
where	O
the	O
boot	B-Operating_System
flag	I-Operating_System
is	O
set	O
.	O
</s>
<s>
DOS	O
and	O
Windows	O
allow	O
only	O
one	O
boot	O
partition	B-Application
to	O
be	O
set	O
with	O
the	O
boot	B-Operating_System
flag	I-Operating_System
.	O
</s>
<s>
Other	O
boot	B-Application
loaders	I-Application
used	O
by	O
third-party	O
boot	B-Application
managers	I-Application
(	O
such	O
as	O
GRUB	B-Application
or	O
XOSL	B-Application
)	O
can	O
be	O
installed	O
to	O
a	O
master	B-Device
boot	I-Device
record	I-Device
and	O
can	O
boot	O
primary	O
or	O
extended	B-Application
partitions	I-Application
,	O
which	O
do	O
not	O
have	O
the	O
boot	B-Operating_System
flag	I-Operating_System
set	O
.	O
</s>
<s>
There	O
are	O
many	O
disk	B-Application
editors	I-Application
that	O
can	O
modify	O
the	O
boot	B-Operating_System
flag	I-Operating_System
,	O
such	O
as	O
Disk	O
Management	O
in	O
Windows	O
,	O
GPartEd	B-Application
in	O
Linux	B-Application
,	O
and	O
fdisk	B-Application
.	O
</s>
<s>
Some	O
BIOSes	O
test	O
if	O
the	O
boot	B-Operating_System
flag	I-Operating_System
of	O
at	O
least	O
one	O
partition	B-Application
is	O
set	O
,	O
otherwise	O
they	O
ignore	O
the	O
device	O
in	O
boot-order	O
.	O
</s>
<s>
Therefore	O
,	O
even	O
if	O
the	O
bootloader	B-Application
does	O
not	O
need	O
the	O
flag	O
,	O
it	O
has	O
to	O
be	O
set	O
to	O
start	O
the	O
boot	O
code	O
from	O
BIOS	B-Operating_System
.	O
</s>
