<s>
A	O
boot	B-Operating_System
disk	I-Operating_System
is	O
a	O
removable	O
digital	B-General_Concept
data	I-General_Concept
storage	I-General_Concept
medium	I-General_Concept
from	O
which	O
a	O
computer	O
can	O
load	O
and	O
run	O
(	O
boot	B-Operating_System
)	O
an	O
operating	B-General_Concept
system	I-General_Concept
or	O
utility	O
program	O
.	O
</s>
<s>
The	O
computer	O
must	O
have	O
a	O
built-in	O
program	O
which	O
will	O
load	O
and	O
execute	O
a	O
program	O
from	O
a	O
boot	B-Operating_System
disk	I-Operating_System
meeting	O
certain	O
standards	O
.	O
</s>
<s>
While	O
almost	O
all	O
modern	O
computers	O
can	O
boot	B-Operating_System
from	O
a	O
hard	O
drive	O
containing	O
the	O
operating	B-General_Concept
system	I-General_Concept
and	O
other	O
software	O
,	O
they	O
would	O
not	O
normally	O
be	O
called	O
boot	B-Operating_System
disks	I-Operating_System
(	O
because	O
they	O
are	O
not	O
removable	O
media	O
)	O
.	O
</s>
<s>
CD-ROMs	B-Device
are	O
the	O
most	O
common	O
forms	O
of	O
media	O
used	O
,	O
but	O
other	O
media	O
,	O
such	O
as	O
magnetic	O
or	O
paper	O
tape	O
drives	O
,	O
ZIP	B-Operating_System
drives	I-Operating_System
,	O
and	O
more	O
recently	O
USB	O
flash	O
drives	O
can	O
be	O
used	O
.	O
</s>
<s>
The	O
computer	O
's	O
BIOS	B-Operating_System
must	O
support	O
booting	B-Operating_System
from	O
the	O
device	O
in	O
question	O
.	O
</s>
<s>
One	O
can	O
make	O
one	O
's	O
own	O
boot	B-Operating_System
disk	I-Operating_System
(	O
typically	O
done	O
to	O
prepare	O
for	O
when	O
the	O
system	O
wo	O
n't	O
start	O
properly	O
)	O
.	O
</s>
<s>
Boot	B-Operating_System
disks	I-Operating_System
are	O
used	O
for	O
:	O
</s>
<s>
for	O
Amiga	B-Application
home	O
computers	O
,	O
running	O
MS-DOS	B-Application
video	O
games	O
on	O
modern	O
computers	O
by	O
using	O
a	O
bootable	B-Operating_System
MS-DOS	B-Application
or	O
FreeDOS	B-Application
USB	O
flash	O
drive	O
)	O
.	O
</s>
<s>
The	O
term	O
boot	B-Operating_System
comes	O
from	O
the	O
idea	O
of	O
lifting	O
oneself	O
by	O
one	O
's	O
own	O
bootstraps	O
:	O
the	O
computer	O
contains	O
a	O
tiny	O
program	O
(	O
bootstrap	B-Operating_System
loader	I-Operating_System
)	O
which	O
will	O
load	O
and	O
run	O
a	O
program	O
found	O
on	O
a	O
boot	B-Operating_System
device	O
.	O
</s>
<s>
This	O
program	O
may	O
itself	O
be	O
a	O
small	O
program	O
designed	O
to	O
load	O
a	O
larger	O
and	O
more	O
capable	O
program	O
,	O
i.e.	O
,	O
the	O
full	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
To	O
enable	O
booting	B-Operating_System
without	O
the	O
requirement	O
either	O
for	O
a	O
mass	B-Device
storage	I-Device
device	I-Device
or	O
to	O
write	O
to	O
the	O
boot	B-Operating_System
medium	O
,	O
it	O
is	O
usual	O
for	O
the	O
boot	B-Operating_System
program	I-Operating_System
to	O
use	O
some	O
system	O
RAM	B-Architecture
as	O
a	O
RAM	B-Application
disk	I-Application
for	O
temporary	O
file	B-Operating_System
storage	O
.	O
</s>
<s>
As	O
an	O
example	O
,	O
any	O
computer	O
compatible	O
with	O
the	O
IBM	B-Device
PC	I-Device
is	O
able	O
with	O
built-in	O
software	O
to	O
load	O
the	O
contents	O
of	O
the	O
first	O
512	O
bytes	O
of	O
a	O
floppy	B-Device
and	O
to	O
execute	O
it	O
if	O
it	O
is	O
a	O
viable	O
program	O
;	O
boot	B-Operating_System
floppies	I-Operating_System
have	O
a	O
very	O
simple	O
loader	O
program	O
in	O
these	O
bytes	O
.	O
</s>
<s>
The	O
process	O
is	O
vulnerable	O
to	O
abuse	O
;	O
data	O
floppies	B-Device
could	O
have	O
a	O
virus	O
written	O
to	O
their	O
first	O
sector	O
which	O
silently	O
infects	O
the	O
host	O
computer	O
if	O
switched	O
on	O
with	O
the	O
disk	O
in	O
the	O
drive	O
.	O
</s>
<s>
Bootable	B-Operating_System
floppy	I-Operating_System
disks	O
(	O
"	O
boot	B-Operating_System
floppies	I-Operating_System
"	O
)	O
for	O
PCs	O
usually	O
contain	O
DOS	B-Device
or	O
miniature	O
versions	O
of	O
Linux	B-Operating_System
.	O
</s>
<s>
The	O
most	O
commonly	O
available	O
floppy	B-Device
disk	I-Device
can	O
hold	O
only	O
1.4	O
MB	O
of	O
data	O
in	O
its	O
standard	O
format	O
,	O
making	O
it	O
impractical	O
for	O
loading	O
large	O
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
The	O
use	O
of	O
boot	B-Operating_System
floppies	I-Operating_System
is	O
in	O
decline	O
,	O
due	O
to	O
the	O
availability	O
of	O
other	O
higher-capacity	O
options	O
,	O
such	O
as	O
CD-ROMs	B-Device
or	O
USB	O
flash	O
drives	O
.	O
</s>
<s>
A	O
modern	O
PC	O
is	O
configured	O
to	O
attempt	O
to	O
boot	B-Operating_System
from	O
various	O
devices	O
in	O
a	O
certain	O
order	O
.	O
</s>
<s>
If	O
a	O
computer	O
is	O
not	O
booting	B-Operating_System
from	O
the	O
device	O
desired	O
,	O
such	O
as	O
the	O
floppy	B-Device
drive	I-Device
,	O
the	O
user	O
may	O
have	O
to	O
enter	O
the	O
BIOS	B-Operating_System
Setup	O
function	O
by	O
pressing	O
a	O
special	O
key	O
when	O
the	O
computer	O
is	O
first	O
turned	O
on	O
(	O
such	O
as	O
,	O
,	O
,	O
or	O
)	O
,	O
and	O
then	O
changing	O
the	O
boot	B-Operating_System
order	O
.	O
</s>
<s>
More	O
recent	O
BIOSes	O
permit	O
the	O
interruption	O
of	O
the	O
final	O
stage	O
of	O
the	O
boot	B-Operating_System
process	I-Operating_System
and	O
invoke	O
the	O
Boot	B-Operating_System
Menu	I-Operating_System
by	O
pressing	O
a	O
function	O
key	O
(	O
usually	O
or	O
)	O
.	O
</s>
<s>
This	O
results	O
in	O
a	O
list	O
of	O
bootable	B-Operating_System
devices	O
being	O
presented	O
,	O
from	O
which	O
a	O
selection	O
may	O
be	O
made	O
.	O
</s>
<s>
Apple	B-Device
silicon	I-Device
Macs	B-Device
display	O
the	O
Boot	B-Operating_System
Menu	I-Operating_System
when	O
the	O
power	O
button	O
is	O
pressed	O
and	O
held	O
,	O
the	O
older	O
Mac	B-Device
computers	I-Device
with	O
Intel	O
processors	O
will	O
display	O
the	O
Boot	B-Operating_System
Menu	I-Operating_System
if	O
user	O
presses	O
the	O
or	O
while	O
the	O
machine	O
is	O
starting	O
.	O
</s>
<s>
Different	O
operating	B-General_Concept
systems	I-General_Concept
use	O
different	O
boot	B-Operating_System
disk	I-Operating_System
contents	O
.	O
</s>
<s>
All	O
boot	B-Operating_System
disks	I-Operating_System
must	O
be	O
compatible	O
with	O
the	O
computer	O
they	O
are	O
designed	O
for	O
.	O
</s>
<s>
All	O
files	O
must	O
be	O
for	O
the	O
same	O
version	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
Complete	O
boot	B-Operating_System
disks	I-Operating_System
can	O
be	O
prepared	O
in	O
one	O
operation	O
by	O
an	O
installed	O
operating	B-General_Concept
system	I-General_Concept
;	O
details	O
vary	O
.	O
</s>
