<s>
The	O
FAT	O
file	B-Application
system	I-Application
is	O
a	O
file	B-Application
system	I-Application
used	O
on	O
MS-DOS	B-Application
and	O
Windows	O
9x	O
family	O
of	O
operating	O
systems	O
.	O
</s>
<s>
It	O
continues	O
to	O
be	O
used	O
on	O
mobile	B-Application
devices	I-Application
and	O
embedded	B-Architecture
systems	I-Architecture
,	O
and	O
thus	O
is	O
a	O
well	O
suited	O
file	B-Application
system	I-Application
for	O
data	O
exchange	O
between	O
computers	O
and	O
devices	O
of	O
almost	O
any	O
type	O
and	O
age	O
from	O
1981	O
through	O
the	O
present	O
.	O
</s>
<s>
A	O
FAT	O
file	B-Application
system	I-Application
is	O
composed	O
of	O
four	O
regions	O
:	O
</s>
<s>
+	O
FAT	O
file	B-Application
system	I-Application
regions	O
,	O
which	O
includes	O
four	O
main	O
regions	O
Region	O
Size	O
in	O
sectors	O
ContentsNotes	O
Reserved	O
sectors	O
(	O
number	O
of	O
reserved	O
sectors	O
)	O
Boot	O
SectorThe	O
first	O
reserved	O
sector	O
(	O
logical	O
sector	O
0	O
)	O
is	O
the	O
Boot	B-Device
Sector	I-Device
(	O
also	O
called	O
Volume	B-Device
Boot	I-Device
Record	I-Device
or	O
simply	O
VBR	B-Device
)	O
.	O
</s>
<s>
It	O
includes	O
an	O
area	O
called	O
the	O
BIOS	B-Device
Parameter	I-Device
Block	I-Device
(	O
BPB	O
)	O
which	O
contains	O
some	O
basic	O
file	B-Application
system	I-Application
information	O
,	O
in	O
particular	O
its	O
type	O
and	O
pointers	O
to	O
the	O
location	O
of	O
the	O
other	O
sections	O
,	O
and	O
usually	O
contains	O
the	O
operating	O
system	O
's	O
boot	B-Application
loader	I-Application
code	O
.	O
</s>
<s>
Important	O
information	O
from	O
the	O
Boot	B-Device
Sector	I-Device
is	O
accessible	O
through	O
an	O
operating	O
system	O
structure	O
called	O
the	O
Drive	O
Parameter	O
Block	O
(	O
DPB	O
)	O
in	O
DOS	O
and	O
OS/2	B-Application
.	O
</s>
<s>
The	O
total	O
count	O
of	O
reserved	O
sectors	O
is	O
indicated	O
by	O
a	O
field	O
inside	O
the	O
Boot	B-Device
Sector	I-Device
,	O
and	O
is	O
usually	O
32	O
on	O
FAT32	B-Application
file	B-Application
systems	I-Application
.	O
</s>
<s>
For	O
FAT32	B-Application
file	B-Application
systems	I-Application
,	O
the	O
reserved	O
sectors	O
include	O
a	O
File	B-Application
System	I-Application
Information	O
Sector	O
at	O
logical	O
sector	O
1	O
and	O
a	O
Backup	O
Boot	B-Device
Sector	I-Device
at	O
logical	O
sector	O
6	O
.	O
</s>
<s>
While	O
many	O
other	O
vendors	O
have	O
continued	O
to	O
utilize	O
a	O
single-sector	O
setup	O
(	O
logical	O
sector	O
0	O
only	O
)	O
for	O
the	O
bootstrap	O
loader	O
,	O
Microsoft	O
's	O
boot	B-Device
sector	I-Device
code	O
has	O
grown	O
to	O
span	O
over	O
logical	O
sectors	O
0	O
and	O
2	O
since	O
the	O
introduction	O
of	O
FAT32	B-Application
,	O
with	O
logical	O
sector	O
0	O
depending	O
on	O
sub-routines	O
in	O
logical	O
sector	O
2	O
.	O
</s>
<s>
The	O
Backup	O
Boot	B-Device
Sector	I-Device
area	O
consists	O
of	O
three	O
logical	O
sectors	O
6	O
,	O
7	O
,	O
and	O
8	O
as	O
well	O
.	O
</s>
<s>
In	O
some	O
cases	O
,	O
Microsoft	O
also	O
uses	O
sector	O
12	O
of	O
the	O
reserved	O
sectors	O
area	O
for	O
an	O
extended	O
boot	B-Application
loader	I-Application
.	O
</s>
<s>
FS	O
Information	O
Sector	O
(	O
FAT32	B-Application
only	O
)	O
More	O
reserved	O
sectors	O
(	O
optional	O
)	O
FAT	O
Region	O
(	O
number	O
of	O
FATs	O
)	O
*	O
(	O
sectors	O
per	O
FAT	O
)	O
File	O
Allocation	O
Table	O
#1This	O
typically	O
contains	O
two	O
copies	O
of	O
the	O
File	O
Allocation	O
Table	O
for	O
the	O
sake	O
of	O
redundancy	O
checking	O
,	O
although	O
rarely	O
used	O
,	O
even	O
by	O
disk	O
repair	O
utilities.These	O
are	O
maps	O
of	O
the	O
Data	O
Region	O
,	O
indicating	O
which	O
clusters	O
are	O
used	O
by	O
files	O
and	O
directories	B-Application
.	O
</s>
<s>
In	O
FAT12	B-Application
and	O
FAT16	B-Application
they	O
immediately	O
follow	O
the	O
reserved	O
sectors.Typically	O
the	O
extra	O
copies	O
are	O
kept	O
in	O
tight	O
synchronization	O
on	O
writes	O
,	O
and	O
on	O
reads	O
they	O
are	O
only	O
used	O
when	O
errors	O
occur	O
in	O
the	O
first	O
FAT	O
.	O
</s>
<s>
File	O
Allocation	O
Table	O
#2	O
...	O
(	O
optional	O
)	O
Root	O
Directory	B-Application
Region	O
(	O
number	O
of	O
root	O
entries	O
*	O
32	O
)	O
/	O
(	O
bytes	O
per	O
sector	O
)	O
Root	O
Directory	B-Application
(	O
FAT12	B-Application
and	O
FAT16	B-Application
only	O
)	O
This	O
is	O
a	O
Directory	B-Application
Table	I-Application
that	O
stores	O
information	O
about	O
the	O
files	O
and	O
directories	B-Application
located	O
in	O
the	O
root	O
directory	B-Application
.	O
</s>
<s>
It	O
is	O
only	O
used	O
with	O
FAT12	B-Application
and	O
FAT16	B-Application
,	O
and	O
imposes	O
on	O
the	O
root	O
directory	B-Application
a	O
fixed	O
maximum	O
size	O
which	O
is	O
pre-allocated	O
at	O
creation	O
of	O
this	O
volume	O
.	O
</s>
<s>
FAT32	B-Application
stores	O
the	O
root	O
directory	B-Application
in	O
the	O
Data	O
Region	O
,	O
along	O
with	O
files	O
and	O
other	O
directories	B-Application
,	O
allowing	O
it	O
to	O
grow	O
without	O
such	O
a	O
constraint	O
.	O
</s>
<s>
Thus	O
,	O
for	O
FAT32	B-Application
,	O
the	O
Data	O
Region	O
starts	O
here	O
.	O
</s>
<s>
Data	O
Region	O
(	O
number	O
of	O
clusters	O
)	O
*	O
(	O
sectors	O
per	O
cluster	O
)	O
Data	O
Region	O
(	O
for	O
files	O
and	O
directories	B-Application
)	O
...	O
(	O
to	O
end	O
of	O
partition	O
or	O
disk	O
)	O
This	O
is	O
where	O
the	O
actual	O
file	O
and	O
directory	B-Application
data	O
is	O
stored	O
and	O
takes	O
up	O
most	O
of	O
the	O
partition	O
.	O
</s>
<s>
Traditionally	O
,	O
the	O
unused	O
parts	O
of	O
the	O
data	O
region	O
are	O
initialized	O
with	O
a	O
filler	O
value	O
of	O
as	O
per	O
the	O
INT	O
1Eh	O
's	O
Disk	O
Parameter	O
Table	O
(	O
DPT	O
)	O
during	O
format	B-Application
on	O
IBM	O
compatible	O
machines	O
,	O
but	O
also	O
used	O
on	O
the	O
Atari	B-Device
Portfolio	I-Device
.	O
</s>
<s>
8-inch	O
CP/M	O
floppies	B-Device
typically	O
came	O
pre-formatted	O
with	O
a	O
value	O
of	O
;	O
by	O
way	O
of	O
Digital	O
Research	O
this	O
value	O
was	O
also	O
used	O
on	O
Atari	B-Device
ST	I-Device
formatted	O
floppies	B-Device
.	O
</s>
<s>
(	O
Some	O
advanced	O
formatting	O
tools	O
allow	O
to	O
configure	O
the	O
format	B-Application
filler	O
byte	O
.	O
</s>
<s>
The	O
size	O
of	O
files	O
and	O
subdirectories	B-Application
can	O
be	O
increased	O
arbitrarily	O
(	O
as	O
long	O
as	O
there	O
are	O
free	O
clusters	O
)	O
by	O
simply	O
adding	O
more	O
links	O
to	O
the	O
file	O
's	O
chain	O
in	O
the	O
FAT	O
.	O
</s>
<s>
FAT32	B-Application
typically	O
commences	O
the	O
Root	O
Directory	B-Application
Table	I-Application
in	O
cluster	O
number	O
2	O
:	O
the	O
first	O
cluster	O
of	O
the	O
Data	O
Region	O
.	O
</s>
<s>
FAT	O
uses	O
little-endian	O
format	B-Application
for	O
all	O
entries	O
in	O
the	O
header	O
(	O
except	O
for	O
,	O
where	O
explicitly	O
mentioned	O
,	O
for	O
some	O
entries	O
on	O
Atari	B-Device
ST	I-Device
boot	B-Device
sectors	I-Device
)	O
and	O
the	O
FAT(s )	O
.	O
</s>
<s>
The	O
total	O
number	O
of	O
sectors	O
(	O
as	O
noted	O
in	O
the	O
boot	B-Device
record	I-Device
)	O
can	O
be	O
larger	O
than	O
the	O
number	O
of	O
sectors	O
used	O
by	O
data	O
(	O
clusters	O
×	O
sectors	O
per	O
cluster	O
)	O
,	O
FATs	O
(	O
number	O
of	O
FATs	O
×	O
sectors	O
per	O
FAT	O
)	O
,	O
the	O
root	O
directory	B-Application
(	O
n/a	O
for	O
FAT32	B-Application
)	O
,	O
and	O
hidden	O
sectors	O
including	O
the	O
boot	B-Device
sector	I-Device
:	O
this	O
would	O
result	O
in	O
unused	O
sectors	O
at	O
the	O
end	O
of	O
the	O
volume	O
.	O
</s>
<s>
If	O
a	O
partition	O
contains	O
more	O
sectors	O
than	O
the	O
total	O
number	O
of	O
sectors	O
occupied	O
by	O
the	O
file	B-Application
system	I-Application
it	O
would	O
also	O
result	O
in	O
unused	O
sectors	O
,	O
at	O
the	O
end	O
of	O
the	O
partition	O
,	O
after	O
the	O
volume	O
.	O
</s>
<s>
On	O
non-partitioned	O
storage	O
devices	O
,	O
such	O
as	O
floppy	B-Device
disks	I-Device
,	O
the	O
Boot	B-Device
Sector	I-Device
(	O
VBR	B-Device
)	O
is	O
the	O
first	O
sector	O
(	O
logical	O
sector	O
0	O
with	O
physical	O
CHS	B-Device
address	O
0/0/1	O
or	O
LBA	B-Device
address	O
0	O
)	O
.	O
</s>
<s>
For	O
partitioned	O
storage	O
devices	O
such	O
as	O
hard	O
disks	O
,	O
the	O
Boot	B-Device
Sector	I-Device
is	O
the	O
first	O
sector	O
of	O
a	O
partition	O
,	O
as	O
specified	O
in	O
the	O
partition	O
table	O
of	O
the	O
device	B-Application
.	O
</s>
<s>
+Common	O
structure	O
of	O
the	O
Boot	B-Device
Sector	I-Device
used	O
by	O
most	O
FAT	O
versions	O
for	O
IBM	O
compatible	O
x86	B-Operating_System
machines	O
since	O
DOS	O
2.0	O
Byte	O
offset	O
Length	O
(	O
bytes	O
)	O
Contents	O
0x000	O
3	O
Jump	O
instruction	O
.	O
</s>
<s>
If	O
the	O
boot	B-Device
sector	I-Device
has	O
a	O
valid	O
signature	O
residing	O
in	O
the	O
last	O
two	O
bytes	O
of	O
the	O
boot	B-Device
sector	I-Device
(	O
tested	O
by	O
most	O
boot	B-Application
loaders	I-Application
residing	O
in	O
the	O
System	O
BIOS	O
or	O
the	O
MBR	B-Device
)	O
and	O
this	O
volume	O
is	O
booted	O
from	O
,	O
the	O
prior	O
boot	B-Application
loader	I-Application
will	O
pass	O
execution	O
to	O
this	O
entry	O
point	O
with	O
certain	O
register	O
values	O
,	O
and	O
the	O
jump	O
instruction	O
will	O
then	O
skip	O
past	O
the	O
rest	O
of	O
the	O
(	O
non-executable	O
)	O
header	O
.	O
</s>
<s>
See	O
Volume	B-Device
Boot	I-Device
Record	I-Device
.	O
</s>
<s>
Since	O
DOS	O
2.0	O
,	O
valid	O
x86-bootable	O
disks	O
must	O
start	O
with	O
either	O
a	O
short	O
jump	O
followed	O
by	O
a	O
NOP	O
(	O
opstring	B-Language
sequence	O
as	O
seen	O
since	O
DOS	O
3.0	O
—	O
and	O
on	O
DOS	O
1.1	O
)	O
or	O
a	O
near	O
jump	O
(	O
as	O
seen	O
on	O
most	O
(	O
Compaq	O
,	O
TeleVideo	O
)	O
DOS	O
2.x	O
formatted	O
disks	O
as	O
well	O
as	O
on	O
some	O
(	O
Epson	O
,	O
Olivetti	O
)	O
DOS	O
3.1	O
disks	O
)	O
.	O
</s>
<s>
For	O
backward	O
compatibility	O
MS-DOS	B-Application
,	O
PC	B-Operating_System
DOS	I-Operating_System
and	O
DR-DOS	B-Application
also	O
accept	O
a	O
jump	O
(	O
)	O
on	O
removable	O
disks	O
.	O
</s>
<s>
On	O
hard	O
disks	O
,	O
DR	O
DOS	O
additionally	O
accepts	O
the	O
swapped	O
JMPS	O
sequence	O
starting	O
with	O
a	O
NOP	O
(	O
)	O
,	O
whereas	O
MS-DOS/PC	O
DOS	O
do	O
not	O
.	O
</s>
<s>
(	O
See	O
below	O
for	O
Atari	B-Device
ST	I-Device
compatibility	O
.	O
)	O
</s>
<s>
The	O
presence	O
of	O
one	O
of	O
these	O
opstring	B-Language
patterns	O
(	O
in	O
combination	O
with	O
a	O
test	O
for	O
a	O
valid	O
media	O
descriptor	O
value	O
at	O
offset	O
)	O
serves	O
as	O
indicator	O
to	O
DOS	O
3.3	O
and	O
higher	O
that	O
some	O
kind	O
of	O
BPB	O
is	O
present	O
(	O
although	O
the	O
exact	O
size	O
should	O
not	O
be	O
determined	O
from	O
the	O
jump	O
target	O
since	O
some	O
boot	B-Device
sectors	I-Device
contain	O
private	O
boot	B-Application
loader	I-Application
data	O
following	O
the	O
BPB	O
)	O
,	O
while	O
for	O
DOS	O
1.x	O
(	O
and	O
some	O
DOS	O
3.0	O
)	O
volumes	O
,	O
they	O
will	O
have	O
to	O
fall	O
back	O
to	O
the	O
DOS	O
1.x	O
method	O
to	O
detect	O
the	O
format	B-Application
via	O
the	O
media	O
byte	O
in	O
the	O
FAT	O
(	O
in	O
logical	O
sector	O
1	O
)	O
.	O
</s>
<s>
Although	O
officially	O
documented	O
as	O
free	O
for	O
OEM	O
use	O
,	O
MS-DOS/PC	O
DOS	O
(	O
since	O
3.1	O
)	O
,	O
Windows	O
95/98/SE/ME	O
and	O
OS/2	B-Application
check	O
this	O
field	O
to	O
determine	O
which	O
other	O
parts	O
of	O
the	O
boot	B-Device
record	I-Device
can	O
be	O
relied	O
upon	O
and	O
how	O
to	O
interpret	O
them	O
.	O
</s>
<s>
Therefore	O
,	O
setting	O
the	O
OEM	O
label	O
to	O
arbitrary	O
or	O
bogus	O
values	O
may	O
cause	O
MS-DOS	B-Application
,	O
PC	O
DOS	O
and	O
OS/2	B-Application
to	O
not	O
recognize	O
the	O
volume	O
properly	O
and	O
cause	O
data	O
corruption	O
on	O
writes	O
.	O
</s>
<s>
Common	O
examples	O
are	O
"	O
IBM␠␠	O
3.3	O
"	O
,	O
"	O
MSDOS5.0	O
"	O
,	O
"	O
MSWIN4.1	O
"	O
,	O
"	O
IBM␠␠	O
7.1	O
"	O
,	O
"	O
mkdosfs␠	O
"	O
,	O
and	O
"	O
FreeDOS␠	B-Application
"	O
.	O
</s>
<s>
?	O
IHC	O
"	O
signatures	O
(	O
a	O
left-over	O
from	O
"	O
␠OGACIHC	O
"	O
for	O
"	O
Chicago	O
"	O
)	O
even	O
on	O
a	O
seemingly	O
read-only	O
disk	O
access	O
(	O
such	O
as	O
a	O
DIR	B-Device
A	O
:	O
)	O
if	O
the	O
medium	O
is	O
not	O
write-protected	O
.	O
</s>
<s>
Given	O
the	O
dependency	O
on	O
certain	O
values	O
explained	O
above	O
,	O
this	O
may	O
,	O
depending	O
on	O
the	O
actual	O
BPB	O
format	B-Application
and	O
contents	O
,	O
cause	O
MS-DOS/PC	O
DOS	O
and	O
OS/2	B-Application
to	O
no	O
longer	O
recognize	O
a	O
medium	O
and	O
throw	O
error	O
messages	O
despite	O
the	O
fact	O
that	O
the	O
medium	O
is	O
not	O
defective	O
and	O
can	O
still	O
be	O
read	O
without	O
problems	O
under	O
other	O
operating	O
systems	O
.	O
</s>
<s>
Some	O
boot	B-Application
loaders	I-Application
make	O
adjustments	O
or	O
refuse	O
to	O
pass	O
control	O
to	O
a	O
boot	B-Device
sector	I-Device
depending	O
on	O
certain	O
values	O
detected	O
here	O
(	O
e.g.	O
,	O
NEWLDR	O
offset	O
)	O
.	O
</s>
<s>
Similarly	O
,	O
the	O
ROM	O
BIOS	O
of	O
the	O
Philips	B-Device
:YES	I-Device
will	O
only	O
boot	O
from	O
a	O
disk	O
if	O
the	O
first	O
four	O
characters	O
of	O
the	O
OEM	O
label	O
are	O
"	O
:YES	O
"	O
.	O
</s>
<s>
If	O
,	O
in	O
an	O
FAT32	B-Application
EBPB	B-Device
,	O
the	O
signature	O
at	O
sector	O
offset	O
is	O
and	O
both	O
total	O
sector	O
entries	O
are	O
0	O
,	O
the	O
file	B-Application
system	I-Application
entry	O
may	O
serve	O
as	O
a	O
64-bit	O
total	O
sector	O
count	O
entry	O
and	O
the	O
OEM	O
label	O
entry	O
may	O
be	O
used	O
as	O
alternative	O
file	B-Application
system	I-Application
type	O
instead	O
of	O
the	O
normal	O
entry	O
at	O
offset	O
.	O
</s>
<s>
In	O
a	O
similar	O
fashion	O
,	O
if	O
this	O
entry	O
is	O
set	O
to	O
"	O
EXFAT␠␠␠	B-Application
"	O
,	O
it	O
indicates	O
the	O
usage	O
of	O
an	O
exFAT	B-Application
BPB	O
located	O
at	O
sector	O
offset	O
to	O
,	O
whereas	O
NTFS	B-Application
volumes	O
use	O
"	O
NTFS␠␠␠␠	O
"	O
to	O
indicate	O
an	O
NTFS	B-Device
BPB	I-Device
.	O
</s>
<s>
0x00B	O
varies	O
BIOS	B-Device
Parameter	I-Device
Block	I-Device
(	O
13	O
,	O
19	O
,	O
21	O
or	O
25	O
bytes	O
)	O
,	O
Extended	B-Device
BIOS	I-Device
Parameter	I-Device
Block	I-Device
(	O
32	O
or	O
51	O
bytes	O
)	O
or	O
FAT32	B-Application
Extended	B-Device
BIOS	I-Device
Parameter	I-Device
Block	I-Device
(	O
60	O
or	O
79	O
bytes	O
)	O
;	O
size	O
and	O
contents	O
varies	O
between	O
operating	O
systems	O
and	O
versions	O
,	O
see	O
below	O
varies	O
varies	O
File	B-Application
system	I-Application
and	O
operating	O
system	O
specific	O
boot	O
code	O
;	O
often	O
starts	O
immediately	O
behind	O
[E]BPB,	O
but	O
sometimes	O
additional	O
"	O
private	O
"	O
boot	B-Application
loader	I-Application
data	O
is	O
stored	O
between	O
the	O
end	O
of	O
the	O
[E]BPB	O
and	O
the	O
start	O
of	O
the	O
boot	O
code	O
;	O
therefore	O
the	O
jump	O
at	O
offset	O
cannot	O
be	O
used	O
to	O
reliably	O
derive	O
the	O
exact	O
[E]BPB	O
format	B-Application
from	O
.	O
</s>
<s>
(	O
In	O
conjunction	O
with	O
at	O
least	O
a	O
DOS	O
3.31	O
BPB	O
some	O
GPT	B-Application
boot	B-Application
loaders	I-Application
(	O
like	O
BootDuet	O
)	O
use	O
–	O
to	O
store	O
the	O
high	O
4	O
bytes	O
of	O
the	O
hidden	O
sectors	O
for	O
volumes	O
located	O
outside	O
the	O
first	O
232-1	O
sectors	O
.	O
</s>
<s>
Since	O
this	O
location	O
may	O
contain	O
code	O
or	O
other	O
data	O
in	O
other	O
boot	B-Device
sectors	I-Device
,	O
it	O
may	O
not	O
be	O
written	O
to	O
when	O
–	O
do	O
not	O
all	O
contain	O
zero	O
.	O
)	O
</s>
<s>
0x1FD	O
1	O
Physical	O
drive	O
number	O
(	O
only	O
in	O
DOS	O
3.2	O
to	O
3.31	O
boot	B-Device
sectors	I-Device
)	O
.	O
</s>
<s>
With	O
OS/2	B-Application
1.0	O
and	O
DOS	O
4.0	O
,	O
this	O
entry	O
moved	O
to	O
sector	O
offset	O
(	O
at	O
offset	O
in	O
the	O
EBPB	B-Device
)	O
.	O
</s>
<s>
Most	O
Microsoft	O
and	O
IBM	O
boot	B-Device
sectors	I-Device
maintain	O
values	O
of	O
at	O
offset	O
and	O
ever	O
since	O
,	O
although	O
they	O
are	O
not	O
part	O
of	O
the	O
signature	O
at	O
.	O
</s>
<s>
If	O
this	O
belongs	O
to	O
a	O
boot	O
volume	O
,	O
the	O
DR-DOS	B-Application
7.07	O
enhanced	O
MBR	B-Device
can	O
be	O
configured	O
(	O
see	O
NEWLDR	O
offset	O
)	O
to	O
dynamically	O
update	O
this	O
entry	O
to	O
the	O
DL	O
value	O
provided	O
at	O
boot	O
time	O
or	O
the	O
value	O
stored	O
in	O
the	O
partition	O
table	O
.	O
</s>
<s>
This	O
enables	O
booting	O
off	O
alternative	O
drives	O
,	O
even	O
when	O
the	O
VBR	B-Device
code	O
ignores	O
the	O
DL	O
value	O
.	O
</s>
<s>
0x1FE	O
2	O
Boot	B-Device
sector	I-Device
signature	O
(	O
)	O
.	O
</s>
<s>
This	O
signature	O
indicates	O
an	O
IBM	O
PC	O
compatible	O
boot	O
code	O
and	O
is	O
tested	O
by	O
most	O
boot	B-Application
loaders	I-Application
residing	O
in	O
the	O
System	O
BIOS	O
or	O
the	O
MBR	B-Device
before	O
passing	O
execution	O
to	O
the	O
boot	B-Device
sector	I-Device
's	O
boot	O
code	O
(	O
but	O
,	O
e.g.	O
,	O
not	O
by	O
the	O
original	O
IBM	O
PC	O
ROM-BIOS	O
)	O
.	O
</s>
<s>
This	O
signature	O
does	O
not	O
indicate	O
a	O
particular	O
file	B-Application
system	I-Application
or	O
operating	O
system	O
.	O
</s>
<s>
Since	O
this	O
signature	O
is	O
not	O
present	O
on	O
all	O
FAT-formatted	O
disks	O
(	O
e.g.	O
,	O
not	O
on	O
DOS	O
1.x	O
or	O
non-x86-bootable	O
FAT	O
volumes	O
)	O
,	O
operating	O
systems	O
must	O
not	O
rely	O
on	O
this	O
signature	O
to	O
be	O
present	O
when	O
logging	O
in	O
volumes	O
(	O
old	O
issues	O
of	O
MS-DOS/PC	O
DOS	O
prior	O
to	O
3.3	O
checked	O
this	O
signature	O
,	O
but	O
newer	O
issues	O
as	O
well	O
as	O
DR-DOS	B-Application
do	O
not	O
)	O
.	O
</s>
<s>
Formatting	O
tools	O
must	O
not	O
write	O
this	O
signature	O
if	O
the	O
written	O
boot	B-Device
sector	I-Device
does	O
not	O
contain	O
at	O
least	O
an	O
x86-compatible	O
dummy	O
boot	B-Application
loader	I-Application
stub	O
;	O
at	O
minimum	O
,	O
it	O
must	O
halt	O
the	O
CPU	O
in	O
an	O
endless	O
loop	O
(	O
)	O
or	O
issue	O
an	O
INT	O
19h	O
and	O
RETF	O
(	O
)	O
.	O
</s>
<s>
These	O
opstrings	B-Language
should	O
not	O
be	O
used	O
at	O
sector	O
offset	O
,	O
however	O
,	O
because	O
DOS	O
tests	O
for	O
other	O
opcodes	B-Language
as	O
signatures	O
.	O
</s>
<s>
Many	O
MSX-DOS	B-Operating_System
2	O
floppies	B-Device
use	O
at	O
sector	O
offset	O
to	O
catch	O
the	O
CPU	O
in	O
a	O
tight	O
loop	O
while	O
maintaining	O
an	O
opcode	B-Language
pattern	O
recognized	O
by	O
MS-DOS/PC	O
DOS	O
.	O
</s>
<s>
Atari	B-Device
STs	I-Device
will	O
assume	O
a	O
disk	O
to	O
be	O
Atari	B-Device
68000	B-Device
bootable	O
if	O
the	O
checksum	B-Algorithm
over	O
the	O
256	O
big-endian	O
words	O
of	O
the	O
boot	B-Device
sector	I-Device
equals	O
.	O
</s>
<s>
If	O
the	O
boot	B-Application
loader	I-Application
code	O
is	O
IBM	O
compatible	O
,	O
it	O
is	O
important	O
to	O
ensure	O
that	O
the	O
checksum	B-Algorithm
over	O
the	O
boot	B-Device
sector	I-Device
does	O
not	O
match	O
this	O
checksum	B-Algorithm
by	O
accident	O
.	O
</s>
<s>
BPB	O
values	O
and	O
FAT12	B-Application
,	O
FAT16	B-Application
and	O
FAT32	B-Application
file	B-Application
systems	I-Application
are	O
meant	O
to	O
use	O
little-endian	O
representation	O
only	O
and	O
there	O
are	O
no	O
known	O
implementations	O
of	O
variants	O
using	O
big-endian	O
values	O
instead	O
.	O
</s>
<s>
+	O
FAT-formatted	O
Atari	B-Device
ST	I-Device
floppies	B-Device
have	O
a	O
very	O
similar	O
boot	B-Device
sector	I-Device
layout	O
Byte	O
offset	O
Length	O
(	O
bytes	O
)	O
Contents	O
0x000	O
2	O
Jump	O
instruction	O
.	O
</s>
<s>
Original	O
Atari	B-Device
ST	I-Device
boot	B-Device
sectors	I-Device
start	O
with	O
a	O
68000	B-Device
BRA.S	O
instruction	O
(	O
)	O
.	O
</s>
<s>
For	O
compatibility	O
with	O
PC	O
operating	O
systems	O
,	O
Atari	B-Device
ST	I-Device
formatted	O
disks	O
since	O
TOS	B-Application
1.4	O
start	O
with	O
instead	O
.	O
</s>
<s>
0x002	O
6	O
OEM	O
Name	O
(	O
padded	O
with	O
spaces	O
)	O
,	O
e.g.	O
,	O
"	O
Loader	O
"	O
(	O
)	O
on	O
volumes	O
containing	O
an	O
Atari	B-Device
ST	I-Device
boot	B-Application
loader	I-Application
.	O
</s>
<s>
0x008	O
3	O
Disk	O
serial	O
number	O
(	O
default	O
:	O
)	O
,	O
used	O
by	O
Atari	B-Device
ST	I-Device
to	O
detect	O
a	O
disk	O
change	O
.	O
</s>
<s>
(	O
Windows	O
9x	O
Volume	O
Tracker	O
will	O
always	O
store	O
"	O
IHC	O
"	O
here	O
on	O
non-write-protected	O
floppy	B-Device
disks	I-Device
;	O
see	O
above	O
.	O
)	O
</s>
<s>
This	O
value	O
must	O
be	O
changed	O
if	O
the	O
disk	O
content	O
is	O
externally	O
changed	O
,	O
otherwise	O
Atari	B-Device
STs	I-Device
may	O
not	O
recognize	O
the	O
change	O
on	O
re-insertion	O
.	O
</s>
<s>
0x00B	O
19	O
DOS	O
3.0	O
BIOS	B-Device
Parameter	I-Device
Block	I-Device
(	O
little-endian	O
format	B-Application
)	O
0x01E	O
varies	O
Private	O
boot	B-Device
sector	I-Device
data	O
(	O
mixed	O
big-endian	O
and	O
little-endian	O
format	B-Application
)	O
varies	O
varies	O
File	B-Application
system	I-Application
and	O
operating	O
system	O
specific	O
Atari	B-Device
ST	I-Device
boot	O
code	O
.	O
</s>
<s>
If	O
loading	O
an	O
operating	O
system	O
(	O
TOS.IMG	O
)	O
fails	O
,	O
the	O
code	O
can	O
return	O
to	O
the	O
Atari	B-Device
ST	I-Device
BIOS	O
with	O
a	O
68000	B-Device
RTS	O
(	O
opcode	B-Language
with	O
big-endian	O
byte	O
sequence	O
)	O
instruction	O
and	O
all	O
registers	O
unaltered	O
.	O
</s>
<s>
0x1FE	O
2	O
Checksum	B-Algorithm
.	O
</s>
<s>
The	O
16-bit	O
checksum	B-Algorithm
over	O
the	O
256	O
big-endian	O
words	O
of	O
the	O
512	O
bytes	O
boot	B-Device
sector	I-Device
including	O
this	O
word	O
must	O
match	O
the	O
magic	O
value	O
in	O
order	O
to	O
indicate	O
an	O
Atari	B-Device
ST	I-Device
68000	B-Device
executable	O
boot	B-Device
sector	I-Device
code	O
.	O
</s>
<s>
This	O
checksum	B-Algorithm
entry	O
can	O
be	O
used	O
to	O
align	O
the	O
checksum	B-Algorithm
accordingly	O
.	O
</s>
<s>
If	O
the	O
logical	O
sector	O
size	O
is	O
larger	O
than	O
512	O
bytes	O
,	O
the	O
remainder	O
is	O
not	O
included	O
in	O
the	O
checksum	B-Algorithm
and	O
is	O
typically	O
zero-filled	O
.	O
</s>
<s>
Since	O
some	O
PC	O
operating	O
systems	O
erroneously	O
do	O
not	O
accept	O
FAT	O
formatted	O
floppies	B-Device
if	O
the	O
signature	O
is	O
not	O
present	O
here	O
,	O
it	O
is	O
advisable	O
to	O
place	O
the	O
in	O
this	O
place	O
(	O
and	O
add	O
an	O
IBM	O
compatible	O
boot	B-Application
loader	I-Application
or	O
stub	O
)	O
and	O
use	O
an	O
unused	O
word	O
in	O
the	O
private	O
data	O
or	O
the	O
boot	O
code	O
area	O
or	O
the	O
serial	O
number	O
in	O
order	O
to	O
ensure	O
that	O
the	O
checksum	B-Algorithm
is	O
not	O
matched	O
(	O
unless	O
the	O
shared	O
fat	O
code	O
overlay	O
would	O
be	O
both	O
IBM	B-Device
PC	I-Device
and	O
Atari	B-Device
ST	I-Device
executable	O
at	O
the	O
same	O
time	O
)	O
.	O
</s>
<s>
+	O
FAT12-formatted	O
MSX-DOS	B-Operating_System
volumes	O
have	O
a	O
very	O
similar	O
boot	B-Device
sector	I-Device
layout	O
Byte	O
offset	O
Length	O
(	O
bytes	O
)	O
Contents	O
0x000	O
3	O
Dummy	O
jump	O
instruction	O
(	O
e.g.	O
,	O
)	O
.	O
</s>
<s>
0x00B	O
19	O
DOS	O
3.0	O
BPB	O
0x01E	O
varies	O
(	O
2	O
)	O
MSX-DOS	B-Operating_System
1	O
code	O
entry	O
point	O
for	O
Z80	O
processors	O
into	O
MSX	O
boot	O
code	O
.	O
</s>
<s>
This	O
is	O
where	O
MSX-DOS	B-Operating_System
1	O
machines	O
jump	O
to	O
when	O
passing	O
control	O
to	O
the	O
boot	B-Device
sector	I-Device
.	O
</s>
<s>
This	O
location	O
overlaps	O
with	O
BPB	O
formats	O
since	O
DOS	O
3.2	O
or	O
the	O
x86	B-Operating_System
compatible	I-Operating_System
boot	B-Device
sector	I-Device
code	O
of	O
IBM	B-Device
PC	I-Device
compatible	O
boot	B-Device
sectors	I-Device
and	O
will	O
lead	O
to	O
a	O
crash	O
on	O
the	O
MSX	O
machine	O
unless	O
special	O
precautions	O
have	O
been	O
taken	O
such	O
as	O
catching	O
the	O
CPU	O
in	O
a	O
tight	O
loop	O
here	O
(	O
opstring	B-Language
for	O
JR	O
)	O
.	O
</s>
<s>
0x020	O
6	O
MSX-DOS	B-Operating_System
2	O
volume	O
signature	O
"	O
VOL_ID	O
"	O
.	O
</s>
<s>
0x026	O
1	O
MSX-DOS	B-Operating_System
2	O
undelete	O
flag	O
(	O
default	O
:	O
.	O
</s>
<s>
If	O
the	O
"	O
VOL_ID	O
"	O
signature	O
is	O
present	O
at	O
sector	O
offset	O
,	O
this	O
flag	O
indicates	O
,	O
if	O
the	O
volume	O
holds	O
deleted	O
files	O
which	O
can	O
be	O
undeleted	O
(	O
see	O
offset	O
in	O
directory	B-Application
entries	O
)	O
.	O
</s>
<s>
0x027	O
4	O
MSX-DOS	B-Operating_System
2	O
disk	O
serial	O
number	O
(	O
default	O
:	O
)	O
.	O
</s>
<s>
If	O
the	O
"	O
VOL_ID	O
"	O
signature	O
is	O
present	O
at	O
sector	O
offset	O
,	O
MSX-DOS	B-Operating_System
2	O
stores	O
a	O
volume	O
serial	O
number	O
here	O
for	O
media	O
change	O
detection	O
.	O
</s>
<s>
0x02B	O
5	O
reserved	O
0x030	O
varies	O
(	O
2	O
)	O
MSX-DOS	B-Operating_System
2	O
code	O
entry	O
point	O
for	O
Z80	O
processors	O
into	O
MSX	O
boot	O
code	O
.	O
</s>
<s>
This	O
is	O
where	O
MSX-DOS	B-Operating_System
2	O
machines	O
jump	O
to	O
when	O
passing	O
control	O
to	O
the	O
boot	B-Device
sector	I-Device
.	O
</s>
<s>
This	O
location	O
overlaps	O
with	O
EBPB	B-Device
formats	O
since	O
DOS	O
4.0	O
/	O
OS/2	B-Application
1.2	O
or	O
the	O
x86	B-Operating_System
compatible	I-Operating_System
boot	B-Device
sector	I-Device
code	O
of	O
IBM	B-Device
PC	I-Device
compatible	O
boot	B-Device
sectors	I-Device
and	O
will	O
lead	O
to	O
a	O
crash	O
on	O
the	O
MSX	O
machine	O
unless	O
special	O
precautions	O
have	O
been	O
taken	O
such	O
as	O
catching	O
the	O
CPU	O
in	O
a	O
tight	O
loop	O
here	O
(	O
opstring	B-Language
for	O
JR	O
)	O
.	O
</s>
<s>
+Common	O
structure	O
of	O
the	O
first	O
25	O
bytes	O
of	O
the	O
BIOS	B-Device
Parameter	I-Device
Block	I-Device
(	O
BPB	O
)	O
used	O
by	O
FAT	O
versions	O
since	O
DOS	O
2.0	O
(	O
bytes	O
at	O
sector	O
offset	O
to	O
are	O
stored	O
since	O
DOS	O
2.0	O
,	O
but	O
not	O
always	O
used	O
before	O
DOS	O
3.2	O
,	O
values	O
at	O
to	O
are	O
used	O
since	O
DOS	O
3.0	O
)	O
Sector	O
offset	O
BPB	O
offset	O
Length	O
(	O
bytes	O
)	O
Contents	O
0x00B	O
0x00	O
2	O
Bytes	O
per	O
logical	O
sector	O
;	O
the	O
most	O
common	O
value	O
is	O
512	O
.	O
</s>
<s>
The	O
minimum	O
allowed	O
value	O
for	O
non-bootable	O
FAT12/FAT16	O
volumes	O
with	O
up	O
to	O
65,535	O
logical	O
sectors	O
is	O
32	O
bytes	O
,	O
or	O
64	O
bytes	O
for	O
more	O
than	O
65,535	O
logical	O
sectors	O
.	O
</s>
<s>
Some	O
pre-DOS	O
3.31	O
OEM	O
versions	O
of	O
DOS	O
used	O
logical	O
sector	O
sizes	O
up	O
to	O
8192	O
bytes	O
for	O
logical	B-Application
sectored	I-Application
FATs	I-Application
.	O
</s>
<s>
Atari	B-Device
ST	I-Device
GEMDOS	B-Operating_System
supports	O
logical	O
sector	O
sizes	O
between	O
512	O
and	O
4096	O
.	O
</s>
<s>
DR-DOS	B-Application
supports	O
booting	O
off	O
FAT12/FAT16	O
volumes	O
with	O
logical	O
sector	O
sizes	O
up	O
to	O
32	O
KB	O
and	O
INT	B-Device
13h	I-Device
implementations	O
supporting	O
physical	O
sectors	O
up	O
to	O
1024	O
bytes/sector	O
.	O
</s>
<s>
The	O
minimum	O
logical	O
sector	O
size	O
for	O
standard	O
FAT32	B-Application
volumes	O
is	O
512	O
bytes	O
,	O
which	O
can	O
be	O
reduced	O
downto	O
128	O
bytes	O
without	O
support	O
for	O
the	O
FS	O
Information	O
Sector	O
.	O
</s>
<s>
Floppy	B-Device
drives	I-Device
and	O
controllers	O
use	O
physical	O
sector	O
sizes	O
of	O
128	O
,	O
256	O
,	O
512	O
and	O
1024	O
bytes	O
(	O
e.g.	O
,	O
PC/AX	O
)	O
.	O
</s>
<s>
The	O
Atari	B-Device
Portfolio	I-Device
supports	O
a	O
sector	O
size	O
of	O
512	O
for	O
volumes	O
larger	O
than	O
64	O
KB	O
,	O
256	O
bytes	O
for	O
volumes	O
larger	O
32	O
KB	O
and	O
128	O
bytes	O
for	O
smaller	O
volumes	O
.	O
</s>
<s>
Magneto-optical	B-Device
drives	I-Device
used	O
sector	O
sizes	O
of	O
512	O
,	O
1024	O
and	O
2048	O
bytes	O
.	O
</s>
<s>
Advanced	B-Device
Format	I-Device
hard	O
disks	O
use	O
4096	O
bytes	O
per	O
sector	O
(	O
4Kn	O
)	O
since	O
2010	O
,	O
but	O
will	O
also	O
be	O
able	O
to	O
emulate	O
512	O
byte	O
sectors	O
(	O
512e	O
)	O
for	O
a	O
transitional	O
period	O
.	O
</s>
<s>
Linux	O
,	O
and	O
by	O
extension	O
Android	O
,	O
supports	O
a	O
logical	O
sector	O
size	O
far	O
larger	O
,	O
officially	O
documented	O
in	O
the	O
Man	O
page	O
for	O
the	O
filesystem	B-Application
utilities	O
as	O
up	O
to	O
32KB	O
.	O
</s>
<s>
Some	O
MS-DOS	B-Application
3.x	O
versions	O
supported	O
a	O
maximum	O
cluster	O
size	O
of	O
4	O
KB	O
only	O
,	O
whereas	O
modern	O
MS-DOS/PC	O
DOS	O
and	O
Windows	B-Application
95	I-Application
support	O
a	O
maximum	O
cluster	O
size	O
of	O
32	O
KB	O
.	O
</s>
<s>
The	O
Windows	B-Device
NT	I-Device
family	I-Device
and	O
some	O
alternative	O
DOS	O
versions	O
such	O
as	O
PTS-DOS	B-Operating_System
fully	O
support	O
64	O
KB	O
clusters	O
.	O
</s>
<s>
For	O
logical	O
sector	O
sizes	O
of	O
1	O
KB	O
,	O
2	O
KB	O
and	O
4	O
KB	O
,	O
Windows	B-Device
NT	I-Device
4.0	O
supports	O
cluster	O
sizes	O
of	O
128	O
KB	O
,	O
while	O
for	O
2	O
KB	O
and	O
4	O
KB	O
sectors	O
the	O
cluster	O
size	O
can	O
reach	O
256	O
KB	O
.	O
</s>
<s>
Some	O
versions	O
of	O
DR-DOS	B-Application
provide	O
limited	O
support	O
for	O
128	O
KB	O
clusters	O
with	O
512	O
bytes/sector	O
using	O
a	O
sectors/cluster	O
value	O
of	O
0	O
.	O
</s>
<s>
MS-DOS/PC	O
DOS	O
will	O
hang	O
on	O
startup	O
if	O
this	O
value	O
is	O
erroneously	O
specified	O
as	O
0	O
.	O
</s>
<s>
The	O
number	O
of	O
logical	O
sectors	O
before	O
the	O
first	O
FAT	O
in	O
the	O
file	B-Application
system	I-Application
image	O
.	O
</s>
<s>
At	O
least	O
1	O
for	O
this	O
sector	O
,	O
usually	O
32	O
for	O
FAT32	B-Application
(	O
to	O
hold	O
the	O
extended	O
boot	B-Device
sector	I-Device
,	O
FS	O
info	O
sector	O
and	O
backup	O
boot	B-Device
sectors	I-Device
)	O
.	O
</s>
<s>
Since	O
DR-DOS	B-Application
7.0x	O
FAT32	B-Application
formatted	O
volumes	O
use	O
a	O
single-sector	O
boot	B-Device
sector	I-Device
,	O
FS	O
info	O
sector	O
and	O
backup	O
sector	O
,	O
some	O
volumes	O
formatted	O
under	O
DR-DOS	B-Application
use	O
a	O
value	O
of	O
4	O
here	O
.	O
</s>
<s>
Almost	O
always	O
2	O
;	O
RAM	B-Application
disks	I-Application
might	O
use	O
1	O
.	O
</s>
<s>
Most	O
versions	O
of	O
MS-DOS/PC	O
DOS	O
do	O
not	O
support	O
more	O
than	O
2	O
FATs	O
.	O
</s>
<s>
Some	O
DOS	O
operating	O
systems	O
support	O
only	O
two	O
FATs	O
in	O
their	O
built-in	O
disk	O
driver	O
,	O
but	O
support	O
other	O
FAT	O
counts	O
for	O
block	O
device	B-Application
drivers	I-Application
loaded	O
later	O
on	O
.	O
</s>
<s>
0x011	O
0x06	O
2	O
Maximum	O
number	O
of	O
FAT12	B-Application
or	O
FAT16	B-Application
root	O
directory	B-Application
entries	O
.	O
</s>
<s>
0	O
for	O
FAT32	B-Application
,	O
where	O
the	O
root	O
directory	B-Application
is	O
stored	O
in	O
ordinary	O
data	O
clusters	O
;	O
see	O
offset	O
in	O
FAT32	B-Application
EBPBs	B-Device
.	O
</s>
<s>
A	O
value	O
of	O
0	O
without	O
a	O
FAT32	B-Application
EBPB	B-Device
(	O
no	O
signature	O
or	O
at	O
offset	O
)	O
may	O
also	O
indicate	O
a	O
variable-sized	O
root	O
directory	B-Application
in	O
some	O
non-standard	O
FAT12	B-Application
and	O
FAT16	B-Application
implementations	I-Application
,	O
which	O
store	O
the	O
root	O
directory	B-Application
start	O
cluster	O
in	O
the	O
cluster	O
1	O
entry	O
in	O
the	O
FAT	O
.	O
</s>
<s>
This	O
value	O
must	O
be	O
adjusted	O
so	O
that	O
directory	B-Application
entries	O
always	O
consume	O
full	O
logical	O
sectors	O
,	O
given	O
that	O
each	O
directory	B-Application
entry	O
takes	O
up	O
32	O
bytes	O
.	O
</s>
<s>
MS-DOS/PC	O
DOS	O
require	O
this	O
value	O
to	O
be	O
a	O
multiple	O
of	O
16	O
.	O
</s>
<s>
The	O
maximum	O
value	O
supported	O
on	O
floppy	B-Device
disks	I-Device
is	O
240	O
,	O
the	O
maximum	O
value	O
supported	O
by	O
MS-DOS/PC	O
DOS	O
on	O
hard	O
disks	O
is	O
512	O
.	O
</s>
<s>
DR-DOS	B-Application
supports	O
booting	O
off	O
FAT12/FAT16	O
volumes	O
,	O
if	O
the	O
boot	O
file	O
is	O
located	O
in	O
the	O
first	O
2048	O
root	O
directory	B-Application
entries	O
.	O
</s>
<s>
0	O
for	O
FAT32	B-Application
.	O
</s>
<s>
Designated	O
for	O
use	O
with	O
custom	O
floppy	B-Device
and	O
superfloppy	O
formats	O
where	O
the	O
geometry	O
is	O
defined	O
in	O
the	O
BPB	O
.	O
</s>
<s>
Certain	O
operating	O
systems	O
before	O
DOS	O
3.2	O
(	O
86-DOS	B-Operating_System
,	O
MS-DOS/PC	O
DOS	O
1.x	O
and	O
MSX-DOS	B-Operating_System
version	O
1.0	O
)	O
ignore	O
the	O
boot	B-Device
sector	I-Device
parameters	O
altogether	O
and	O
use	O
the	O
media	O
descriptor	O
value	O
from	O
the	O
first	O
byte	O
of	O
the	O
FAT	O
to	O
choose	O
among	O
internally	O
pre-defined	O
parameter	O
templates	O
.	O
</s>
<s>
On	O
removable	O
drives	O
,	O
DR-DOS	B-Application
will	O
assume	O
the	O
presence	O
of	O
a	O
BPB	O
if	O
this	O
value	O
is	O
greater	O
or	O
equal	O
to	O
,	O
whereas	O
for	O
fixed	O
disks	O
,	O
it	O
must	O
be	O
to	O
assume	O
the	O
presence	O
of	O
a	O
BPB	O
.	O
</s>
<s>
Initially	O
,	O
these	O
values	O
were	O
meant	O
to	O
be	O
used	O
as	O
bit	O
flags	O
;	O
for	O
any	O
removable	O
media	O
without	O
a	O
recognized	O
BPB	O
format	B-Application
and	O
a	O
media	O
descriptor	O
of	O
either	O
or	O
to	O
MS-DOS/PC	O
DOS	O
treats	O
bit	O
1	O
as	O
a	O
flag	O
to	O
choose	O
a	O
9-sectors	O
per	O
track	O
format	B-Application
rather	O
than	O
an	O
8-sectors	O
format	B-Application
,	O
and	O
bit	O
0	O
as	O
a	O
flag	O
to	O
indicate	O
double-sided	O
media	O
.	O
</s>
<s>
0x016	O
0x0B	O
2	O
Logical	O
sectors	O
per	O
File	O
Allocation	O
Table	O
for	O
FAT12/FAT16	O
.	O
</s>
<s>
FAT32	B-Application
sets	O
this	O
to	O
0	O
and	O
uses	O
the	O
32-bit	O
value	O
at	O
offset	O
instead	O
.	O
</s>
<s>
MS-DOS	B-Application
3.10	O
still	O
supported	O
the	O
DOS	O
2.0	O
format	B-Application
,	O
but	O
could	O
use	O
the	O
DOS	O
3.0	O
format	B-Application
as	O
well	O
.	O
</s>
<s>
Sector	O
offset	O
BPB	O
offset	O
Length	O
(	O
bytes	O
)	O
Contents	O
0x00B	O
0x00	O
13	O
DOS	O
2.0	O
BPB	O
0x018	O
0x0D	O
2	O
Physical	O
sectors	O
per	O
track	O
for	O
disks	O
with	O
INT	B-Device
13h	I-Device
CHS	B-Device
geometry	O
,	O
e.g.	O
,	O
15	O
for	O
a	O
"	O
1.20	O
MB	O
"	O
(	O
1200	O
KB	O
)	O
floppy	B-Device
.	O
</s>
<s>
0x01A	O
0x0F	O
2	O
Number	O
of	O
heads	O
for	O
disks	O
with	O
INT	O
13h	O
CHS	B-Device
geometry	O
,	O
e.g.	O
,	O
2	O
for	O
a	O
double	O
sided	O
floppy	B-Device
.	O
</s>
<s>
A	O
bug	O
in	O
all	O
versions	O
of	O
MS-DOS/PC	O
DOS	O
up	O
to	O
including	O
7.10	O
causes	O
these	O
operating	O
systems	O
to	O
crash	O
for	O
CHS	B-Device
geometries	O
with	O
256	O
heads	O
,	O
therefore	O
almost	O
all	O
BIOSes	O
choose	O
a	O
maximum	O
of	O
255	O
heads	O
only	O
.	O
</s>
<s>
Officially	O
,	O
MS-DOS	B-Application
3.20	O
still	O
used	O
the	O
DOS	O
3.0	O
format	B-Application
,	O
but	O
SYS	B-Language
and	O
FORMAT	B-Application
were	O
adapted	O
to	O
support	O
a	O
6	O
bytes	O
longer	O
format	B-Application
already	O
(	O
of	O
which	O
not	O
all	O
entries	O
were	O
used	O
)	O
.	O
</s>
<s>
Officially	O
introduced	O
with	O
DOS	O
3.31	O
and	O
not	O
used	O
by	O
DOS	O
3.2	O
,	O
some	O
DOS	O
3.2	O
utilities	O
were	O
designed	O
to	O
be	O
aware	O
of	O
this	O
new	O
format	B-Application
already	O
.	O
</s>
<s>
Sector	O
offset	O
BPB	O
offset	O
Length	O
(	O
bytes	O
)	O
Contents	O
0x00B	O
0x00	O
13	O
DOS	O
2.0	O
BPB	O
0x018	O
0x0D	O
2	O
Physical	O
sectors	O
per	O
track	O
for	O
disks	O
with	O
INT	B-Device
13h	I-Device
CHS	B-Device
geometry	O
,	O
e.g.	O
,	O
18	O
for	O
a	O
"	O
1.44	O
MB	O
"	O
(	O
1440	O
KB	O
)	O
floppy	B-Device
.	O
</s>
<s>
Unused	O
for	O
drives	O
,	O
which	O
do	O
n't	O
support	O
CHS	B-Device
access	O
any	O
more	O
.	O
</s>
<s>
A	O
value	O
of	O
0	O
may	O
indicate	O
LBA-only	O
access	O
,	O
but	O
may	O
cause	O
a	O
divide-by-zero	O
exception	O
in	O
some	O
boot	B-Application
loaders	I-Application
,	O
which	O
can	O
be	O
avoided	O
by	O
storing	O
a	O
neutral	O
value	O
of	O
1	O
here	O
,	O
if	O
no	O
CHS	B-Device
geometry	O
can	O
be	O
reasonably	O
emulated	O
.	O
</s>
<s>
0x01A	O
0x0F	O
2	O
Number	O
of	O
heads	O
for	O
disks	O
with	O
INT	O
13h	O
CHS	B-Device
geometry	O
,	O
e.g.	O
,	O
2	O
for	O
a	O
double	O
sided	O
floppy	B-Device
.	O
</s>
<s>
Unused	O
for	O
drives	O
,	O
which	O
do	O
n't	O
support	O
CHS	B-Device
access	O
any	O
more	O
.	O
</s>
<s>
A	O
bug	O
in	O
all	O
versions	O
of	O
MS-DOS/PC	O
DOS	O
up	O
to	O
including	O
7.10	O
causes	O
these	O
operating	O
systems	O
to	O
crash	O
for	O
CHS	B-Device
geometries	O
with	O
256	O
heads	O
,	O
therefore	O
almost	O
all	O
BIOSes	O
choose	O
a	O
maximum	O
of	O
255	O
heads	O
only	O
.	O
</s>
<s>
A	O
value	O
of	O
0	O
may	O
indicate	O
LBA-only	O
access	O
,	O
but	O
may	O
cause	O
a	O
divide-by-zero	O
exception	O
in	O
some	O
boot	B-Application
loaders	I-Application
,	O
which	O
can	O
be	O
avoided	O
by	O
storing	O
a	O
neutral	O
value	O
of	O
1	O
here	O
,	O
if	O
no	O
CHS	B-Device
geometry	O
can	O
be	O
reasonably	O
emulated	O
.	O
</s>
<s>
If	O
this	O
belongs	O
to	O
an	O
Advanced	O
Active	O
Partition	O
(	O
AAP	O
)	O
selected	O
at	O
boot	O
time	O
,	O
the	O
BPB	O
entry	O
will	O
be	O
dynamically	O
updated	O
by	O
the	O
enhanced	O
MBR	B-Device
to	O
reflect	O
the	O
"	O
relative	O
sectors	O
"	O
value	O
in	O
the	O
partition	O
table	O
,	O
stored	O
at	O
offset	O
in	O
the	O
AAP	O
or	O
NEWLDR	O
MBR	B-Device
,	O
so	O
that	O
it	O
becomes	O
possible	O
to	O
boot	O
the	O
operating	O
system	O
from	O
EBRs	O
.	O
</s>
<s>
(	O
Some	O
GPT	B-Application
boot	B-Application
loaders	I-Application
(	O
like	O
BootDuet	O
)	O
use	O
boot	B-Device
sector	I-Device
offsets	O
–	O
to	O
store	O
the	O
high	O
4	O
bytes	O
of	O
a	O
64-bit	O
hidden	O
sectors	O
value	O
for	O
volumes	O
located	O
outside	O
the	O
first	O
232−1	O
sectors	O
.	O
)	O
</s>
<s>
Officially	O
,	O
it	O
must	O
be	O
used	O
only	O
if	O
the	O
logical	O
sectors	O
entry	O
at	O
offset	O
is	O
zero	O
,	O
but	O
some	O
operating	O
systems	O
(	O
some	O
old	O
versions	O
of	O
DR	B-Application
DOS	I-Application
)	O
use	O
this	O
entry	O
also	O
for	O
smaller	O
disks	O
.	O
</s>
<s>
For	O
partitioned	O
media	O
,	O
if	O
this	O
and	O
the	O
entry	O
at	O
are	O
both	O
0	O
(	O
as	O
seen	O
on	O
some	O
DOS	O
3.x	O
FAT16	B-Application
volumes	O
)	O
,	O
many	O
operating	O
systems	O
(	O
including	O
MS-DOS/PC	O
DOS	O
)	O
will	O
retrieve	O
the	O
value	O
from	O
the	O
corresponding	O
partition	O
's	O
entry	O
(	O
at	O
offset	O
)	O
in	O
the	O
MBR	B-Device
instead	O
.	O
</s>
<s>
some	O
DR-DOS	B-Application
volumes	O
with	O
32-bit	O
cluster	O
entries	O
)	O
can	O
use	O
a	O
64-bit	O
entry	O
at	O
offset	O
instead	O
.	O
</s>
<s>
Determine	O
(	O
once	O
)	O
SSA	O
=	O
RSC+FN×SF+ceil( ( 32×RDE	O
)	O
/SS	O
)	O
,	O
where	O
the	O
reserved	O
sector	O
count	O
RSC	O
is	O
stored	O
at	O
offset	O
,	O
the	O
number	O
of	O
FATsFN	O
at	O
offset	O
,	O
the	O
sectors	O
per	O
FAT	O
SF	O
at	O
offset	O
(	O
FAT12/FAT16	O
)	O
or	O
(	O
FAT32	B-Application
)	O
,	O
the	O
root	O
directory	B-Application
entries	O
RDE	O
at	O
offset	O
,	O
the	O
sector	O
size	O
SS	O
at	O
offset	O
,	O
and	O
ceil(x )	O
rounds	O
up	O
to	O
a	O
whole	O
number	O
.	O
</s>
<s>
On	O
unpartitioned	O
media	O
the	O
volume	O
's	O
number	O
of	O
hidden	O
sectors	O
is	O
zero	O
and	O
therefore	O
LSN	O
and	O
LBA	B-Device
addresses	O
become	O
the	O
same	O
for	O
as	O
long	O
as	O
a	O
volume	O
's	O
logical	O
sector	O
size	O
is	O
identical	O
to	O
the	O
underlying	O
medium	O
's	O
physical	O
sector	O
size	O
.	O
</s>
<s>
Under	O
these	O
conditions	O
,	O
it	O
is	O
also	O
simple	O
to	O
translate	O
between	O
CHS	B-Device
addresses	O
and	O
LSNs	O
as	O
well	O
:	O
</s>
<s>
Track	O
number	O
TN	O
,	O
head	O
number	O
HN	O
,	O
and	O
sector	O
number	O
SN	O
correspond	O
to	O
Cylinder-head-sector	B-Device
:	O
the	O
formula	O
gives	O
the	O
known	O
CHS	B-Device
to	O
LBA	B-Device
translation	O
.	O
</s>
<s>
Further	O
structure	O
used	O
by	O
FAT12	B-Application
and	O
FAT16	B-Application
since	O
OS/2	B-Application
1.0	O
and	O
DOS	O
4.0	O
,	O
also	O
known	O
as	O
Extended	B-Device
BIOS	I-Device
Parameter	I-Device
Block	I-Device
(	O
EBPB	B-Device
)	O
(	O
bytes	O
below	O
sector	O
offset	O
are	O
the	O
same	O
as	O
for	O
the	O
DOS	O
3.31	O
BPB	O
)	O
:	O
</s>
<s>
Sector	O
offset	O
EBPB	B-Device
offset	O
Length	O
(	O
bytes	O
)	O
Contents	O
0x00B	O
0x00	O
25	O
DOS	O
3.31	O
BPB	O
0x024	O
0x19	O
1	O
Physical	O
drive	O
number	O
(	O
for	O
(	O
first	O
)	O
removable	O
media	O
,	O
for	O
(	O
first	O
)	O
fixed	O
disk	O
as	O
per	O
INT	B-Device
13h	I-Device
)	O
.	O
</s>
<s>
Some	O
boot	B-Application
loaders	I-Application
such	O
as	O
the	O
MS-DOS/PC	O
DOS	O
boot	B-Application
loader	I-Application
use	O
this	O
value	O
when	O
loading	O
the	O
operating	O
system	O
,	O
others	O
ignore	O
it	O
altogether	O
or	O
use	O
the	O
drive	O
number	O
provided	O
in	O
the	O
DL	O
register	O
by	O
the	O
underlying	O
boot	B-Application
loader	I-Application
(	O
e.g.	O
,	O
with	O
many	O
BIOSes	O
and	O
MBRs	O
)	O
.	O
</s>
<s>
The	O
entry	O
is	O
sometimes	O
changed	O
by	O
the	O
SYS	B-Language
command	I-Language
or	O
it	O
can	O
be	O
dynamically	O
fixed	O
up	O
by	O
the	O
prior	O
bootstrap	O
loader	O
in	O
order	O
to	O
force	O
the	O
boot	B-Device
sector	I-Device
code	O
to	O
load	O
the	O
operating	O
system	O
from	O
alternative	O
physical	O
disks	O
than	O
the	O
default	O
.	O
</s>
<s>
A	O
similar	O
entry	O
existed	O
(	O
only	O
)	O
in	O
DOS	O
3.2	O
to	O
3.31	O
boot	B-Device
sectors	I-Device
at	O
sector	O
offset	O
.	O
</s>
<s>
If	O
this	O
belongs	O
to	O
a	O
boot	O
volume	O
,	O
the	O
DR-DOS	B-Application
7.07	O
enhanced	O
MBR	B-Device
can	O
be	O
configured	O
(	O
see	O
NEWLDR	O
offset	O
)	O
to	O
dynamically	O
update	O
this	O
EBPB	B-Device
entry	O
to	O
the	O
DL	O
value	O
provided	O
at	O
boot	O
time	O
or	O
the	O
value	O
stored	O
in	O
the	O
partition	O
table	O
.	O
</s>
<s>
This	O
enables	O
booting	O
off	O
alternative	O
drives	O
,	O
even	O
when	O
the	O
VBR	B-Device
code	O
ignores	O
the	O
DL	O
value	O
.	O
</s>
<s>
In	O
some	O
MS-DOS/PC	O
DOS	O
boot	O
code	O
used	O
as	O
a	O
scratchpad	O
for	O
the	O
INT	B-Device
13h	I-Device
current	O
head	O
high	O
byte	O
for	O
the	O
assumed	O
16-bit	O
word	O
at	O
offset	O
.	O
</s>
<s>
Some	O
DR-DOS	B-Application
FAT12/FAT16	O
boot	B-Device
sectors	I-Device
use	O
this	O
entry	O
as	O
a	O
scratchpad	O
as	O
well	O
,	O
but	O
for	O
different	O
purposes	O
.	O
</s>
<s>
VGA-Copy	B-Device
stores	O
a	O
CRC	O
over	O
the	O
system	O
's	O
ROM-BIOS	O
in	O
this	O
location	O
.	O
</s>
<s>
Some	O
boot	B-Application
managers	I-Application
use	O
this	O
entry	O
to	O
communicate	O
the	O
desired	O
drive	O
letter	O
under	O
which	O
the	O
volume	O
should	O
occur	O
to	O
operating	O
systems	O
such	O
as	O
OS/2	B-Application
by	O
setting	O
bit	O
7	O
and	O
specifying	O
the	O
drive	O
number	O
in	O
bits	O
6-0	O
(	O
C	O
:	O
=	O
value	O
0	O
,	O
D	O
:	O
=	O
value	O
1	O
,	O
...	O
)	O
.	O
</s>
<s>
Since	O
this	O
normally	O
affects	O
the	O
in-memory	O
image	O
of	O
the	O
boot	B-Device
sector	I-Device
only	O
,	O
this	O
does	O
not	O
cause	O
compatibility	O
problems	O
with	O
other	O
uses	O
;	O
</s>
<s>
In	O
Windows	B-Device
NT	I-Device
used	O
for	O
CHKDSK	B-Device
flags	O
(	O
bits	O
7-2	O
always	O
cleared	O
,	O
bit	O
1	O
:	O
disk	O
I/O	O
errors	O
encountered	O
,	O
possible	O
bad	O
sectors	O
,	O
run	O
surface	O
scan	O
on	O
next	O
boot	O
,	O
bit	O
0	O
:	O
volume	O
is	O
"	O
dirty	O
"	O
and	O
was	O
not	O
properly	O
unmounted	O
before	O
shutdown	O
,	O
run	O
CHKDSK	B-Device
on	O
next	O
boot	O
)	O
.	O
</s>
<s>
(	O
Should	O
be	O
to	O
indicate	O
that	O
an	O
EBPB	B-Device
with	O
the	O
following	O
3	O
entries	O
exists	O
(	O
since	O
OS/2	B-Application
1.2	O
and	O
DOS	O
4.0	O
)	O
.	O
</s>
<s>
Can	O
be	O
on	O
some	O
OS/2	B-Application
1.0-1.1	O
and	O
PC	O
DOS	O
3.4	O
disks	O
indicating	O
an	O
earlier	O
form	O
of	O
the	O
EBPB	B-Device
format	B-Application
with	O
only	O
the	O
serial	O
number	O
following	O
.	O
</s>
<s>
MS-DOS/PC	O
DOS	O
4.0	O
and	O
higher	O
,	O
OS/2	B-Application
1.2	O
and	O
higher	O
as	O
well	O
as	O
the	O
Windows	B-Device
NT	I-Device
family	I-Device
recognize	O
both	O
signatures	O
accordingly	O
.	O
)	O
</s>
<s>
Alternatively	O
,	O
some	O
DR-DOS	B-Application
disk	O
utilities	O
provide	O
a	O
/	O
#	O
option	O
to	O
generate	O
a	O
human-readable	O
time	O
stamp	O
"	O
mmdd-hhmm	O
"	O
build	O
from	O
BCD-encoded	O
8-bit	O
values	O
for	O
the	O
month	O
,	O
day	O
,	O
hour	O
and	O
minute	O
instead	O
of	O
a	O
serial	O
number	O
.	O
</s>
<s>
0x02B	O
0x20	O
11	O
Partition	O
Volume	O
Label	O
,	O
padded	O
with	O
blanks	O
(	O
)	O
,	O
e.g.	O
,	O
"	O
NO␠NAME␠␠␠␠	O
"	O
Software	O
changing	O
the	O
directory	B-Application
volume	O
label	O
in	O
the	O
file	B-Application
system	I-Application
should	O
also	O
update	O
this	O
entry	O
,	O
but	O
not	O
all	O
software	O
does	O
.	O
</s>
<s>
Supported	O
since	O
OS/2	B-Application
1.2	O
and	O
MS-DOS	B-Application
4.0	O
and	O
higher	O
.	O
</s>
<s>
This	O
area	O
was	O
used	O
by	O
boot	B-Device
sectors	I-Device
of	O
DOS	O
3.2	O
to	O
3.3	O
to	O
store	O
a	O
private	O
copy	O
of	O
the	O
Disk	O
Parameter	O
Table	O
(	O
DPT	O
)	O
instead	O
of	O
using	O
the	O
INT	O
1Eh	O
pointer	O
to	O
retrieve	O
the	O
ROM	O
table	O
as	O
in	O
later	O
issues	O
of	O
the	O
boot	B-Device
sector	I-Device
.	O
</s>
<s>
This	O
entry	O
is	O
meant	O
for	O
display	O
purposes	O
only	O
and	O
must	O
not	O
be	O
used	O
by	O
the	O
operating	O
system	O
to	O
identify	O
the	O
type	O
of	O
the	O
file	B-Application
system	I-Application
.	O
</s>
<s>
Supported	O
since	O
OS/2	B-Application
1.2	O
and	O
MS-DOS	B-Application
4.0	O
and	O
higher	O
.	O
</s>
<s>
In	O
essence	O
FAT32	B-Application
inserts	O
28	O
bytes	O
into	O
the	O
EBPB	B-Device
,	O
followed	O
by	O
the	O
remaining	O
26	O
(	O
or	O
sometimes	O
only	O
7	O
)	O
EBPB	B-Device
bytes	O
as	O
shown	O
above	O
for	O
FAT12	B-Application
and	O
FAT16	B-Application
.	O
</s>
<s>
Microsoft	O
and	O
IBM	O
operating	O
systems	O
determine	O
the	O
type	O
of	O
FAT	O
file	B-Application
system	I-Application
used	O
on	O
a	O
volume	O
solely	O
by	O
the	O
number	O
of	O
clusters	O
,	O
not	O
by	O
the	O
used	O
BPB	O
format	B-Application
or	O
the	O
indicated	O
file	B-Application
system	I-Application
type	O
,	O
that	O
is	O
,	O
it	O
is	O
technically	O
possible	O
to	O
use	O
a	O
"	O
FAT32	B-Application
EBPB	B-Device
"	O
also	O
for	O
FAT12	B-Application
and	O
FAT16	B-Application
volumes	O
as	O
well	O
as	O
a	O
DOS	O
4.0	O
EBPB	B-Device
for	O
small	O
FAT32	B-Application
volumes	O
.	O
</s>
<s>
Sector	O
offset	O
FAT32	B-Application
EBPB	B-Device
offset	O
Length	O
(	O
bytes	O
)	O
Contents	O
0x00B	O
0x00	O
25	O
DOS	O
3.31	O
BPB	O
0x024	O
0x19	O
4	O
Logical	O
sectors	O
per	O
file	O
allocation	O
table	O
(	O
corresponds	O
with	O
the	O
old	O
entry	O
at	O
offset	O
0x0B	O
in	O
the	O
DOS	O
2.0	O
BPB	O
)	O
.	O
</s>
<s>
The	O
byte	O
at	O
offset	O
in	O
this	O
entry	O
should	O
never	O
become	O
or	O
in	O
order	O
to	O
avoid	O
any	O
misinterpretation	O
with	O
the	O
EBPB	B-Device
format	B-Application
under	O
non-FAT32	O
aware	O
operating	O
systems	O
.	O
</s>
<s>
Fortunately	O
,	O
under	O
normal	O
circumstances	O
(	O
sector	O
size	O
of	O
512	O
bytes	O
)	O
,	O
this	O
cannot	O
happen	O
,	O
as	O
a	O
FAT32	B-Application
file	B-Application
system	I-Application
has	O
at	O
most	O
0xffffff6	O
=	O
268435446	O
clusters	O
.	O
</s>
<s>
DR-DOS	B-Application
7.07	O
FAT32	B-Application
boot	B-Device
sectors	I-Device
with	O
dual	O
LBA	B-Device
and	O
CHS	B-Device
support	O
utilize	O
bits	O
15-8	O
to	O
store	O
an	O
access	O
flag	O
and	O
part	O
of	O
a	O
message	O
.	O
</s>
<s>
These	O
bits	O
contain	O
either	O
bit	O
pattern	O
(	O
low-case	O
letter	O
'	O
o	O
 '	O
,	O
bit	O
13	O
set	O
for	O
CHS	B-Device
access	O
)	O
or	O
(	O
upper-case	O
letter	O
'	O
O	O
 '	O
,	O
bit	O
13	O
cleared	O
for	O
LBA	B-Device
access	O
)	O
.	O
</s>
<s>
Formatting	O
tools	O
or	O
non-DR	O
SYS-type	O
tools	O
may	O
clear	O
these	O
bits	O
,	O
but	O
other	O
disk	O
tools	O
should	O
leave	O
bits	O
15-8	O
unchanged	O
.	O
</s>
<s>
FAT32	B-Application
implementations	I-Application
should	O
refuse	O
to	O
mount	O
volumes	O
with	O
version	O
numbers	O
unknown	O
by	O
them	O
.	O
</s>
<s>
0x02C	O
0x21	O
4	O
Cluster	O
number	O
of	O
root	O
directory	B-Application
start	O
,	O
typically	O
2	O
(	O
first	O
cluster	O
)	O
if	O
it	O
contains	O
no	O
bad	O
sector	O
.	O
</s>
<s>
(	O
Microsoft	O
's	O
FAT32	B-Application
implementation	I-Application
imposes	O
an	O
artificial	O
limit	O
of	O
65,535	O
entries	O
per	O
directory	B-Application
,	O
whilst	O
many	O
third-party	O
implementations	O
do	O
not	O
.	O
)	O
</s>
<s>
A	O
cluster	O
value	O
of	O
0	O
is	O
not	O
officially	O
allowed	O
and	O
can	O
never	O
indicate	O
a	O
valid	O
root	O
directory	B-Application
start	O
cluster	O
.	O
</s>
<s>
Some	O
non-standard	O
FAT32	B-Application
implementations	I-Application
may	O
treat	O
it	O
as	O
an	O
indicator	O
to	O
search	O
for	O
a	O
fixed-sized	O
root	O
directory	B-Application
where	O
it	O
would	O
be	O
expected	O
on	O
FAT16	B-Application
volumes	O
;	O
see	O
offset	O
.	O
</s>
<s>
0x030	O
0x25	O
2	O
Logical	O
sector	O
number	O
of	O
FS	O
Information	O
Sector	O
,	O
typically	O
1	O
,	O
i.e.	O
,	O
the	O
second	O
of	O
the	O
three	O
FAT32	B-Application
boot	B-Device
sectors	I-Device
.	O
</s>
<s>
Some	O
FAT32	B-Application
implementations	I-Application
support	O
a	O
slight	O
variation	O
of	O
Microsoft	O
's	O
specification	O
in	O
making	O
the	O
FS	O
Information	O
Sector	O
optional	O
by	O
specifying	O
a	O
value	O
of	O
(	O
or	O
)	O
in	O
this	O
entry	O
.	O
</s>
<s>
Since	O
logical	O
sector	O
0	O
can	O
never	O
be	O
a	O
valid	O
FS	O
Information	O
Sector	O
,	O
but	O
FS	O
Information	O
Sectors	O
use	O
the	O
same	O
signature	O
as	O
found	O
on	O
many	O
boot	B-Device
sectors	I-Device
,	O
file	B-Application
system	I-Application
implementations	O
should	O
never	O
attempt	O
to	O
use	O
logical	O
sector	O
0	O
as	O
FS	O
Information	O
sector	O
and	O
instead	O
assume	O
that	O
the	O
feature	O
is	O
unsupported	O
on	O
that	O
particular	O
volume	O
.	O
</s>
<s>
Without	O
a	O
FS	O
Information	O
Sector	O
,	O
the	O
minimum	O
allowed	O
logical	O
sector	O
size	O
of	O
FAT32	B-Application
volumes	O
can	O
be	O
reduced	O
downto	O
128	O
bytes	O
for	O
special	O
purposes	O
.	O
</s>
<s>
0x032	O
0x27	O
2	O
First	O
logical	O
sector	O
number	O
of	O
a	O
copy	O
of	O
the	O
three	O
FAT32	B-Application
boot	B-Device
sectors	I-Device
,	O
typically	O
6	O
.	O
</s>
<s>
Since	O
DR-DOS	B-Application
7.0x	O
FAT32	B-Application
formatted	O
volumes	O
use	O
a	O
single-sector	O
boot	B-Device
sector	I-Device
,	O
some	O
volumes	O
formatted	O
under	O
DR-DOS	B-Application
use	O
a	O
value	O
of	O
2	O
here	O
.	O
</s>
<s>
0x034	O
0x29	O
12	O
Reserved	O
(	O
may	O
be	O
changed	O
to	O
format	B-Application
filler	O
byte	O
as	O
an	O
artifact	O
by	O
MS-DOS	B-Application
FDISK	B-Application
,	O
must	O
be	O
initialized	O
to	O
0	O
by	O
formatting	O
tools	O
,	O
but	O
must	O
not	O
be	O
changed	O
by	O
file	B-Application
system	I-Application
implementations	O
or	O
disk	O
tools	O
later	O
on	O
.	O
)	O
</s>
<s>
DR-DOS	B-Application
7.07	O
FAT32	B-Application
boot	B-Device
sectors	I-Device
use	O
these	O
12	O
bytes	O
to	O
store	O
the	O
filename	O
of	O
the	O
"	O
IBMBIO␠␠COM	O
"	O
file	O
to	O
be	O
loaded	O
(	O
up	O
to	O
the	O
first	O
29,696	O
bytes	O
or	O
the	O
actual	O
file	O
size	O
,	O
whatever	O
is	O
smaller	O
)	O
and	O
executed	O
by	O
the	O
boot	B-Device
sector	I-Device
,	O
followed	O
by	O
a	O
terminating	O
NUL	O
(	O
)	O
character	O
.	O
</s>
<s>
exFAT	B-Application
BPBs	O
are	O
located	O
at	O
sector	O
offset	O
to	O
,	O
overlapping	O
all	O
the	O
remaining	O
entries	O
of	O
a	O
standard	O
FAT32	B-Application
EBPB	B-Device
including	O
this	O
one	O
.	O
</s>
<s>
They	O
can	O
be	O
detected	O
via	O
their	O
OEM	O
label	O
signature	O
"	O
EXFAT␠␠␠	B-Application
"	O
at	O
sector	O
offset	O
.	O
</s>
<s>
May	O
hold	O
format	B-Application
filler	O
byte	O
artifacts	O
after	O
partitioning	O
with	O
MS-DOS	B-Application
FDISK	B-Application
,	O
but	O
not	O
yet	O
formatted	O
.	O
</s>
<s>
Most	O
FAT32	B-Application
file	B-Application
system	I-Application
implementations	O
do	O
not	O
support	O
an	O
alternative	O
signature	O
of	O
to	O
indicate	O
a	O
shortened	O
form	O
of	O
the	O
FAT32	B-Application
EBPB	B-Device
with	O
only	O
the	O
serial	O
number	O
following	O
(	O
and	O
no	O
Volume	O
Label	O
and	O
File	B-Application
system	I-Application
type	O
entries	O
)	O
,	O
but	O
since	O
these	O
19	O
mostly	O
unused	O
bytes	O
might	O
serve	O
different	O
purposes	O
in	O
some	O
scenarios	O
,	O
implementations	O
should	O
accept	O
as	O
an	O
alternative	O
signature	O
and	O
then	O
fall	O
back	O
to	O
use	O
the	O
directory	B-Application
volume	O
label	O
in	O
the	O
file	B-Application
system	I-Application
instead	O
of	O
in	O
the	O
EBPB	B-Device
for	O
compatibility	O
with	O
potential	O
extensions	O
.	O
</s>
<s>
for	O
FAT12/FAT16	O
(	O
Volume	O
ID	O
)	O
0x047	O
0x3C	O
11	O
Cf	O
.	O
</s>
<s>
for	O
FAT12/FAT16	O
(	O
File	B-Application
system	I-Application
type	O
,	O
padded	O
with	O
blanks	O
(	O
)	O
,	O
e.g.	O
,	O
"	O
FAT32␠␠␠	O
"	O
)	O
.	O
</s>
<s>
If	O
both	O
total	O
logical	O
sectors	O
entries	O
at	O
offset	O
and	O
are	O
0	O
on	O
volumes	O
using	O
a	O
FAT32	B-Application
EBPB	B-Device
with	O
signature	O
,	O
volumes	O
with	O
more	O
than	O
4,294,967,295	O
(	O
232-1	O
)	O
sectors	O
(	O
f.e.	O
</s>
<s>
some	O
DR-DOS	B-Application
volumes	O
with	O
32-bit	O
cluster	O
entries	O
)	O
can	O
use	O
this	O
entry	O
as	O
64-bit	O
total	O
logical	O
sectors	O
entry	O
instead	O
.	O
</s>
<s>
In	O
this	O
case	O
,	O
the	O
OEM	O
label	O
at	O
sector	O
offset	O
may	O
be	O
retrieved	O
as	O
new-style	O
file	B-Application
system	I-Application
type	O
instead	O
.	O
</s>
<s>
Versions	O
of	O
DOS	O
before	O
3.2	O
totally	O
or	O
partially	O
relied	O
on	O
the	O
media	O
descriptor	O
byte	O
in	O
the	O
BPB	O
or	O
the	O
FAT	O
ID	O
byte	O
in	O
cluster	O
0	O
of	O
the	O
first	O
FAT	O
in	O
order	O
to	O
determine	O
FAT12	B-Application
diskette	B-Device
formats	O
even	O
if	O
a	O
BPB	O
is	O
present	O
.	O
</s>
<s>
Originally	O
,	O
the	O
FAT	O
ID	O
was	O
meant	O
to	O
be	O
a	O
bit	O
flag	O
with	O
all	O
bits	O
set	O
except	O
for	O
bit	O
2	O
cleared	O
to	O
indicate	O
an	O
80	O
track	O
(	O
vs	O
.	O
40	O
track	O
)	O
format	B-Application
,	O
bit	O
1	O
cleared	O
to	O
indicate	O
a	O
9	O
sector	O
(	O
vs	O
.	O
8	O
sector	O
)	O
format	B-Application
,	O
and	O
bit	O
0	O
cleared	O
to	O
indicate	O
a	O
single-sided	O
(	O
vs	O
.	O
double-sided	O
)	O
format	B-Application
,	O
but	O
this	O
scheme	O
was	O
not	O
followed	O
by	O
all	O
OEMs	O
and	O
became	O
obsolete	O
with	O
the	O
introduction	O
of	O
hard	O
disks	O
and	O
high-density	O
formats	O
.	O
</s>
<s>
Also	O
,	O
the	O
various	O
8-inch	O
formats	O
supported	O
by	O
86-DOS	B-Operating_System
and	O
MS-DOS	B-Application
do	O
not	O
fit	O
this	O
scheme	O
.	O
</s>
<s>
FAT	O
ID	O
(	O
compare	O
with	O
media	O
ID	O
at	O
BPB	O
offset	O
)	O
Size	O
8	B-Device
"	I-Device
5.25	B-Device
"	I-Device
8	B-Device
"	I-Device
8	B-Device
"	I-Device
5.25	B-Device
"	I-Device
8	B-Device
"	I-Device
8	B-Device
"	I-Device
5.25	B-Device
"	I-Device
5.25	B-Device
"	I-Device
5.25	B-Device
"	I-Device
/	O
3.5	B-Device
"	I-Device
5.25	B-Device
"	I-Device
/	O
3.5	B-Device
"	I-Device
5.25	B-Device
"	I-Device
3.5	B-Device
"	I-Device
3.5	B-Device
"	I-Device
5.25	B-Device
"	I-Device
5.25	B-Device
"	I-Device
/	O
3.5	B-Device
"	I-Device
3.5	B-Device
"	I-Device
3.5	B-Device
"	I-Device
3.5	B-Device
"	I-Device
5.25	B-Device
"	I-Device
8	B-Device
"	I-Device
Density	O
DD	O
48tpi	O
SD	O
DD	O
DD	O
48tpi	O
SD	O
SD	O
DD	O
48tpi	O
DD	O
48tpi	O
HD	O
96tpi	O
DD	O
135tpi	O
HD	O
135tpi	O
QD	O
96tpi	O
DD	O
HD	O
135tpi	O
ED	O
QD	O
96tpi	O
SD	O
Modulation	O
MFM	O
FM	O
MFM	O
MFM	O
FM	O
FM	O
MFM	O
MFM	O
MFM	O
MFM	O
MFM	O
MFM	O
MFM	O
MFM	O
MFM	O
MFM	O
MFM	O
MFM	O
MFM	O
FM	O
Formatted	O
capacity	O
(	O
KB	O
)	O
320	O
250	O
(	O
"	O
old	O
"	O
)	O
1200	O
160	O
250	O
(	O
"	O
new	O
"	O
)	O
500	O
360	O
180	O
640	O
320	O
1200	O
720	O
1440	O
720	O
360	O
360	O
1440	O
2880	O
720	O
243	O
/	O
250	O
Cylinders	O
(	O
CHS	B-Device
)	O
77	O
40	O
77	O
77	O
40	O
77	O
77	O
40	O
40	O
80	O
80	O
80	O
80	O
80	O
80	O
80	O
80	O
80	O
80	O
80	O
77	O
Physical	O
sectors	O
/	O
track	O
(	O
BPB	O
offset	O
)	O
8	O
26	O
8	O
8	O
26	O
26	O
9	O
9	O
8	O
8	O
15	O
9	O
18	O
9	O
(	O
8	O
)	O
9	O
9	O
18	O
36	O
9	O
(	O
8	O
)	O
26	O
Number	O
of	O
heads	O
(	O
BPB	O
offset	O
)	O
2	O
1	O
2	O
(	O
1	O
)	O
1	O
1	O
2	O
2	O
1	O
2	O
1	O
2	O
2	O
2	O
2	O
1	O
1	O
2	O
2	O
2	O
1	O
Byte	O
payload	O
/	O
physical	O
sector	O
512	O
128	O
1024	O
512	O
128	O
128	O
512	O
512	O
512	O
512	O
512	O
512	O
512	O
512	O
512	O
512	O
512	O
512	O
512	O
128	O
Bytes	O
/	O
logical	O
sector	O
(	O
BPB	O
offset	O
)	O
512	O
128	O
1024	O
512	O
128	O
128	O
512	O
512	O
512	O
512	O
512	O
512	O
512	O
512	O
512	O
512	O
512	O
512	O
512	O
128	O
Logical	O
sectors	O
/	O
cluster	O
(	O
BPB	O
offset	O
)	O
2	O
4	O
1	O
1	O
4	O
4	O
2	O
1	O
2	O
1	O
(	O
2	O
?	O
)	O
</s>
<s>
1	O
2	O
1	O
2	O
1	O
2	O
4	O
Reserved	O
logical	O
sectors	O
(	O
BPB	O
offset	O
)	O
1	O
1	O
1	O
1	O
4	O
4	O
1	O
1	O
1	O
1	O
1	O
1	O
(	O
2	O
)	O
1	O
1	O
1	O
1	O
1	O
1	O
1	O
Number	O
of	O
FATs	O
(	O
BPB	O
offset	O
)	O
2	O
2	O
2	O
2	O
2	O
2	O
2	O
2	O
2	O
2	O
2	O
2	O
2	O
2	O
2	O
2	O
2	O
2	O
2	O
2	O
Root	O
directory	B-Application
entries	O
(	O
BPB	O
offset	O
)	O
112	O
(	O
7	O
sectors	O
)	O
68	O
(	O
17	O
sectors	O
)	O
192	O
(	O
6	O
sectors	O
)	O
64	O
(	O
4	O
sectors	O
)	O
68	O
(	O
17	O
sectors	O
)	O
68	O
(	O
17	O
sectors	O
)	O
112	O
(	O
7	O
sectors	O
)	O
64	O
(	O
4	O
sectors	O
)	O
112	O
(	O
7	O
sectors	O
)	O
112	O
(	O
7	O
sectors	O
)	O
224	O
(	O
14	O
sectors	O
)	O
112	O
(	O
7	O
sectors	O
)	O
224	O
(	O
14	O
sectors	O
)	O
112	O
(	O
7	O
sectors	O
)	O
224	O
(	O
14	O
sectors	O
)	O
240	O
(	O
15	O
sectors	O
)	O
64	O
(	O
16	O
sectors	O
)	O
Total	O
logical	O
sectors	O
(	O
BPB	O
offset	O
)	O
640	O
2002	O
1232	O
(	O
616	O
)	O
320	O
2002	O
4004	O
720	O
360	O
1280	O
640	O
2400	O
1440	O
2880	O
720	O
2880	O
5760	O
2002	O
Logical	O
sectors	O
/	O
FAT	O
(	O
BPB	O
offset	O
)	O
1	O
6	O
2	O
1	O
6	O
6	O
?	O
</s>
<s>
The	O
table	O
does	O
not	O
list	O
a	O
number	O
of	O
incompatible	O
8-inch	O
and	O
5.25-inch	O
FAT12	B-Application
floppy	B-Device
formats	O
supported	O
by	O
86-DOS	B-Operating_System
,	O
which	O
differ	O
either	O
in	O
the	O
size	O
of	O
the	O
directory	B-Application
entries	O
(	O
16	O
bytes	O
vs.	O
32	O
bytes	O
)	O
or	O
in	O
the	O
extent	O
of	O
the	O
reserved	O
sectors	O
area	O
(	O
several	O
whole	O
tracks	O
vs.	O
one	O
logical	O
sector	O
only	O
)	O
.	O
</s>
<s>
The	O
implementation	O
of	O
a	O
single-sided	O
315	O
KB	O
FAT12	B-Application
format	B-Application
used	O
in	O
MS-DOS	B-Application
for	O
the	O
Apricot	O
PC	O
and	O
F1e	O
had	O
a	O
different	O
boot	B-Device
sector	I-Device
layout	O
,	O
to	O
accommodate	O
that	O
computer	O
's	O
non-IBM	O
compatible	O
BIOS	O
.	O
</s>
<s>
The	O
jump	O
instruction	O
and	O
OEM	O
name	O
were	O
omitted	O
,	O
and	O
the	O
MS-DOS	B-Application
BPB	O
parameters	O
(	O
offsets	O
-	O
in	O
the	O
standard	O
boot	B-Device
sector	I-Device
)	O
were	O
located	O
at	O
offset	O
.	O
</s>
<s>
The	O
Portable	B-Device
,	O
F1	O
,	O
PC	O
duo	O
and	O
Xi	O
FD	O
supported	O
a	O
non-standard	O
double-sided	O
720	O
KB	O
FAT12	B-Application
format	B-Application
instead	O
.	O
</s>
<s>
The	O
differences	O
in	O
the	O
boot	B-Device
sector	I-Device
layout	O
and	O
media	O
IDs	O
made	O
these	O
formats	O
incompatible	O
with	O
many	O
other	O
operating	O
systems	O
.	O
</s>
<s>
315	O
KB	O
:	O
Bytes	O
per	O
logical	O
sector	O
:	O
512	O
bytes	O
,	O
logical	O
sectors	O
per	O
cluster	O
:	O
1	O
,	O
reserved	O
logical	O
sectors	O
:	O
1	O
,	O
number	O
of	O
FATs	O
:	O
2	O
,	O
root	O
directory	B-Application
entries	O
:	O
128	O
,	O
total	O
logical	O
sectors	O
:	O
630	O
,	O
FAT	O
ID	O
:	O
,	O
logical	O
sectors	O
per	O
FAT	O
:	O
2	O
,	O
physical	O
sectors	O
per	O
track	O
:	O
9	O
,	O
number	O
of	O
heads	O
:	O
1	O
.	O
</s>
<s>
720	O
KB	O
:	O
Bytes	O
per	O
logical	O
sector	O
:	O
512	O
bytes	O
,	O
logical	O
sectors	O
per	O
cluster	O
:	O
2	O
,	O
reserved	O
logical	O
sectors	O
:	O
1	O
,	O
number	O
of	O
FATs	O
:	O
2	O
,	O
root	O
directory	B-Application
entries	O
:	O
176	O
,	O
total	O
logical	O
sectors	O
:	O
1440	O
,	O
FAT	O
ID	O
:	O
,	O
logical	O
sectors	O
per	O
FAT	O
:	O
3	O
,	O
physical	O
sectors	O
per	O
track	O
:	O
9	O
,	O
number	O
of	O
heads	O
:	O
2	O
.	O
</s>
<s>
Later	O
versions	O
of	O
Apricot	O
MS-DOS	B-Application
gained	O
the	O
ability	O
to	O
read	O
and	O
write	O
disks	O
with	O
the	O
standard	O
boot	B-Device
sector	I-Device
in	O
addition	O
to	O
those	O
with	O
the	O
Apricot	O
one	O
.	O
</s>
<s>
These	O
formats	O
were	O
also	O
supported	O
by	O
DOS	B-Operating_System
Plus	I-Operating_System
2.1e/g	O
for	O
the	O
Apricot	O
ACT	O
series	O
.	O
</s>
<s>
The	O
DOS	B-Operating_System
Plus	I-Operating_System
adaptation	O
for	O
the	O
BBC	B-Device
Master	I-Device
512	I-Device
supported	O
two	O
FAT12	B-Application
formats	O
on	O
80-track	O
,	O
double-sided	O
,	O
double-density	O
5.25	B-Device
"	I-Device
drives	O
,	O
which	O
did	O
not	O
use	O
conventional	O
boot	B-Device
sectors	I-Device
at	O
all	O
.	O
</s>
<s>
800	O
KB	O
data	O
disks	O
omitted	O
a	O
boot	B-Device
sector	I-Device
and	O
began	O
with	O
a	O
single	O
copy	O
of	O
the	O
FAT	O
.	O
</s>
<s>
640	O
KB	O
boot	O
disks	O
began	O
with	O
a	O
miniature	O
ADFS	B-Device
file	B-Application
system	I-Application
containing	O
the	O
boot	B-Application
loader	I-Application
,	O
followed	O
by	O
a	O
single	O
FAT	O
.	O
</s>
<s>
Also	O
,	O
the	O
640	O
KB	O
format	B-Application
differed	O
by	O
using	O
physical	O
CHS	B-Device
sector	O
numbers	O
starting	O
with	O
0	O
(	O
not	O
1	O
,	O
as	O
common	O
)	O
and	O
incrementing	O
sectors	O
in	O
the	O
order	O
sector-track-head	O
(	O
not	O
sector-head-track	O
,	O
as	O
common	O
)	O
.	O
</s>
<s>
800	O
KB	O
:	O
Bytes	O
per	O
logical	O
sector	O
:	O
1024	O
bytes	O
,	O
logical	O
sectors	O
per	O
cluster	O
:	O
1	O
,	O
reserved	O
logical	O
sectors	O
:	O
0	O
,	O
number	O
of	O
FATs	O
:	O
1	O
,	O
root	O
directory	B-Application
entries	O
:	O
192	O
,	O
total	O
logical	O
sectors	O
:	O
800	O
,	O
FAT	O
ID	O
:	O
,	O
logical	O
sectors	O
per	O
FAT	O
:	O
2	O
,	O
physical	O
sectors	O
per	O
track	O
:	O
5	O
,	O
number	O
of	O
heads	O
:	O
2	O
.	O
</s>
<s>
640	O
KB	O
:	O
Bytes	O
per	O
logical	O
sector	O
:	O
256	O
bytes	O
,	O
logical	O
sectors	O
per	O
cluster	O
:	O
8	O
,	O
reserved	O
logical	O
sectors	O
:	O
16	O
,	O
number	O
of	O
FATs	O
:	O
1	O
,	O
root	O
directory	B-Application
entries	O
:	O
112	O
,	O
total	O
logical	O
sectors	O
:	O
2560	O
,	O
FAT	O
ID	O
:	O
,	O
logical	O
sectors	O
per	O
FAT	O
:	O
2	O
,	O
physical	O
sectors	O
per	O
track	O
:	O
16	O
,	O
number	O
of	O
heads	O
:	O
2	O
.	O
</s>
<s>
DOS	B-Operating_System
Plus	I-Operating_System
for	O
the	O
Master	O
512	O
could	O
also	O
access	O
standard	O
PC	O
disks	O
formatted	O
to	O
or	O
,	O
using	O
the	O
first	O
byte	O
of	O
the	O
FAT	O
in	O
logical	O
sector	O
1	O
to	O
determine	O
the	O
capacity	O
.	O
</s>
<s>
The	O
DEC	O
Rainbow	O
100	O
(	O
all	O
variations	O
)	O
supported	O
one	O
FAT12	B-Application
format	B-Application
on	O
80-track	O
,	O
single-sided	O
,	O
quad-density	O
5.25	B-Device
"	I-Device
drives	O
.	O
</s>
<s>
The	O
first	O
two	O
tracks	O
were	O
reserved	O
for	O
the	O
boot	B-Application
loader	I-Application
,	O
but	O
did	O
n't	O
contain	O
an	O
MBR	B-Device
nor	O
a	O
BPB	O
(	O
MS-DOS	B-Application
used	O
a	O
static	O
in-memory	O
BPB	O
instead	O
)	O
.	O
</s>
<s>
The	O
boot	B-Device
sector	I-Device
(	O
track	O
0	O
,	O
side	O
0	O
,	O
sector	O
1	O
)	O
was	O
Z80	O
code	O
beginning	O
with	O
DI	O
.	O
</s>
<s>
The	O
file	B-Application
system	I-Application
starts	O
on	O
track	O
2	O
,	O
side	O
0	O
,	O
sector	O
1	O
.	O
</s>
<s>
There	O
are	O
2	O
copies	O
of	O
the	O
FAT	O
and	O
96	O
entries	O
in	O
the	O
root	O
directory	B-Application
.	O
</s>
<s>
The	O
"	O
FS	O
Information	O
Sector	O
"	O
was	O
introduced	O
in	O
FAT32	B-Application
for	O
speeding	O
up	O
access	O
times	O
of	O
certain	O
operations	O
(	O
in	O
particular	O
,	O
getting	O
the	O
amount	O
of	O
free	O
space	O
)	O
.	O
</s>
<s>
It	O
is	O
located	O
at	O
a	O
logical	O
sector	O
number	O
specified	O
in	O
the	O
FAT32	B-Application
EBPB	B-Device
boot	B-Device
record	I-Device
at	O
position	O
(	O
usually	O
logical	O
sector	O
1	O
,	O
immediately	O
after	O
the	O
boot	B-Device
record	I-Device
itself	O
)	O
.	O
</s>
<s>
For	O
as	O
long	O
as	O
the	O
FS	O
Information	O
Sector	O
is	O
located	O
in	O
logical	O
sector	O
1	O
,	O
the	O
location	O
,	O
where	O
the	O
FAT	O
typically	O
started	O
in	O
FAT12	B-Application
and	O
FAT16	B-Application
file	B-Application
systems	I-Application
(	O
with	O
only	O
one	O
reserved	O
sectors	O
)	O
,	O
the	O
presence	O
of	O
this	O
signature	O
ensures	O
that	O
early	O
versions	O
of	O
DOS	O
will	O
never	O
attempt	O
to	O
mount	O
a	O
FAT32	B-Application
volume	O
,	O
as	O
they	O
expect	O
the	O
values	O
in	O
cluster	O
0	O
and	O
cluster	O
1	O
to	O
follow	O
certain	O
bit	O
patterns	O
,	O
which	O
are	O
not	O
met	O
by	O
this	O
signature	O
.	O
</s>
<s>
0x004	O
480	O
Reserved	O
(	O
byte	O
values	O
should	O
be	O
set	O
to	O
during	O
format	B-Application
,	O
but	O
not	O
be	O
relied	O
upon	O
and	O
never	O
changed	O
later	O
on	O
)	O
0x1E4	O
4	O
FS	O
information	O
sector	O
signature	O
(	O
=	O
"	O
rrAa	O
"	O
)	O
0x1E8	O
4	O
Last	O
known	O
number	O
of	O
free	O
data	O
clusters	O
on	O
the	O
volume	O
,	O
or	O
if	O
unknown	O
.	O
</s>
<s>
Should	O
be	O
set	O
to	O
during	O
format	B-Application
and	O
updated	O
by	O
the	O
operating	O
system	O
later	O
on	O
.	O
</s>
<s>
Should	O
be	O
set	O
to	O
during	O
format	B-Application
and	O
updated	O
by	O
the	O
operating	O
system	O
later	O
on	O
.	O
</s>
<s>
0x1F0	O
12	O
Reserved	O
(	O
byte	O
values	O
should	O
be	O
set	O
to	O
during	O
format	B-Application
,	O
but	O
not	O
be	O
relied	O
upon	O
and	O
never	O
changed	O
later	O
on	O
)	O
0x1FC	O
4	O
FS	O
information	O
sector	O
signature	O
(	O
)	O
(	O
All	O
four	O
bytes	O
should	O
match	O
before	O
the	O
contents	O
of	O
this	O
sector	O
should	O
be	O
assumed	O
to	O
be	O
in	O
valid	O
format	B-Application
.	O
)	O
</s>
<s>
Therefore	O
,	O
operating	O
systems	O
should	O
first	O
inspect	O
a	O
volume	O
's	O
optional	O
shutdown	O
status	O
bitflags	O
residing	O
in	O
the	O
FAT	O
entry	O
of	O
cluster	O
1	O
or	O
the	O
FAT32	B-Application
EBPB	B-Device
at	O
offset	O
and	O
ignore	O
the	O
data	O
stored	O
in	O
the	O
FS	O
information	O
sector	O
,	O
if	O
these	O
bitflags	O
indicate	O
that	O
the	O
volume	O
was	O
not	O
properly	O
unmounted	O
before	O
.	O
</s>
<s>
This	O
does	O
not	O
cause	O
any	O
problems	O
other	O
than	O
a	O
possible	O
speed	O
penalty	O
for	O
the	O
first	O
free	O
space	O
query	O
or	O
data	O
cluster	O
allocation	O
;	O
see	O
fragmentation	B-Architecture
.	O
</s>
<s>
If	O
this	O
sector	O
is	O
present	O
on	O
a	O
FAT32	B-Application
volume	O
,	O
the	O
minimum	O
allowed	O
logical	O
sector	O
size	O
is	O
512bytes	O
,	O
whereas	O
otherwise	O
it	O
would	O
be	O
128bytes	O
.	O
</s>
<s>
Some	O
FAT32	B-Application
implementations	I-Application
support	O
a	O
slight	O
variation	O
of	O
Microsoft	O
's	O
specification	O
by	O
making	O
the	O
FS	O
information	O
sector	O
optional	O
by	O
specifying	O
a	O
value	O
of	O
(	O
or	O
)	O
in	O
the	O
entry	O
at	O
offset	O
.	O
</s>
<s>
Cluster	O
sizes	O
vary	O
depending	O
on	O
the	O
type	O
of	O
FAT	O
file	B-Application
system	I-Application
being	O
used	O
and	O
the	O
size	O
of	O
the	O
drive	O
;	O
typical	O
cluster	O
sizes	O
range	O
from	O
2	O
to	O
.	O
</s>
<s>
Thus	O
,	O
a	O
file	O
is	O
represented	O
by	O
a	O
chain	O
of	O
clusters	O
(	O
referred	O
to	O
as	O
a	O
singly	O
linked	B-Data_Structure
list	I-Data_Structure
)	O
.	O
</s>
<s>
Each	O
version	O
of	O
the	O
FAT	O
file	B-Application
system	I-Application
uses	O
a	O
different	O
size	O
for	O
FAT	O
entries	O
.	O
</s>
<s>
The	O
FAT12	B-Application
file	B-Application
system	I-Application
uses	O
12	O
bits	O
per	O
FAT	O
entry	O
,	O
thus	O
two	O
entries	O
span	O
3	O
bytes	O
.	O
</s>
<s>
The	O
FAT16	B-Application
file	B-Application
system	I-Application
uses	O
16	O
bits	O
per	O
FAT	O
entry	O
,	O
thus	O
one	O
entry	O
spans	O
two	O
bytes	O
in	O
little-endian	O
byte	O
order	O
:	O
</s>
<s>
The	O
FAT32	B-Application
file	B-Application
system	I-Application
uses	O
32	O
bits	O
per	O
FAT	O
entry	O
,	O
thus	O
one	O
entry	O
spans	O
four	O
bytes	O
in	O
little-endian	O
byte	O
order	O
.	O
</s>
<s>
For	O
very	O
early	O
versions	O
of	O
DOS	O
to	O
recognize	O
the	O
file	B-Application
system	I-Application
,	O
the	O
system	O
must	O
have	O
been	O
booted	O
from	O
the	O
volume	O
or	O
the	O
volume	O
's	O
FAT	O
must	O
start	O
with	O
the	O
volume	O
's	O
second	O
sector	O
(	O
logical	O
sector	O
1	O
with	O
physical	O
CHS	B-Device
address	O
0/0/2	O
or	O
LBA	B-Device
address	O
1	O
)	O
,	O
that	O
is	O
,	O
immediately	O
following	O
the	O
boot	B-Device
sector	I-Device
.	O
</s>
<s>
Operating	O
systems	O
assume	O
this	O
hard-wired	O
location	O
of	O
the	O
FAT	O
in	O
order	O
to	O
find	O
the	O
FAT	O
ID	O
in	O
the	O
FAT	O
's	O
cluster	O
0	O
entry	O
on	O
DOS	O
1.0-1.1	O
FAT	O
diskettes	B-Device
,	O
where	O
no	O
valid	O
BPB	O
is	O
found	O
.	O
</s>
<s>
The	O
first	O
entry	O
(	O
cluster	O
0	O
in	O
the	O
FAT	O
)	O
holds	O
the	O
FAT	O
ID	O
since	O
MS-DOS	B-Application
1.20	O
and	O
PC	B-Operating_System
DOS	I-Operating_System
1.1	O
(	O
allowed	O
values	O
-	O
with	O
-	O
reserved	O
)	O
in	O
bits	O
7-0	O
,	O
which	O
is	O
also	O
copied	O
into	O
the	O
BPB	O
of	O
the	O
boot	B-Device
sector	I-Device
,	O
offset	O
since	O
DOS	O
2.0	O
.	O
</s>
<s>
The	O
remaining	O
4	O
bits	O
(	O
if	O
FAT12	B-Application
)	O
,	O
8	O
bits	O
(	O
if	O
FAT16	B-Application
)	O
or	O
20	O
bits	O
(	O
if	O
FAT32	B-Application
)	O
of	O
this	O
entry	O
are	O
always	O
1	O
.	O
</s>
<s>
Additionally	O
,	O
for	O
FAT	O
IDs	O
other	O
than	O
(	O
and	O
)	O
it	O
is	O
possible	O
to	O
determine	O
the	O
correct	O
nibble	O
and	O
byte	O
order	O
(	O
to	O
be	O
)	O
used	O
by	O
the	O
file	B-Application
system	I-Application
driver	O
,	O
however	O
,	O
the	O
FAT	O
file	B-Application
system	I-Application
officially	O
uses	O
a	O
little-endian	O
representation	O
only	O
and	O
there	O
are	O
no	O
known	O
implementations	O
of	O
variants	O
using	O
big-endian	O
values	O
instead	O
.	O
</s>
<s>
86-DOS	B-Operating_System
0.42	O
up	O
to	O
MS-DOS	B-Application
1.14	O
used	O
hard-wired	O
drive	O
profiles	O
instead	O
of	O
a	O
FAT	O
ID	O
,	O
but	O
used	O
this	O
byte	O
to	O
distinguish	O
between	O
media	O
formatted	O
with	O
32-byte	O
or	O
16-byte	O
directory	B-Application
entries	O
,	O
as	O
they	O
were	O
used	O
prior	O
to	O
86-DOS	B-Operating_System
0.42	O
.	O
</s>
<s>
The	O
second	O
entry	O
(	O
cluster	O
1	O
in	O
the	O
FAT	O
)	O
nominally	O
stores	O
the	O
end-of-cluster-chain	O
marker	O
as	O
used	O
by	O
the	O
formater	O
,	O
but	O
typically	O
always	O
holds	O
/	O
/	O
,	O
that	O
is	O
,	O
with	O
the	O
exception	O
of	O
bits	O
31-28	O
on	O
FAT32	B-Application
volumes	O
these	O
bits	O
are	O
normally	O
always	O
set	O
.	O
</s>
<s>
Since	O
DOS	O
7.1	O
the	O
two	O
most-significant	O
bits	O
of	O
this	O
cluster	O
entry	O
may	O
hold	O
two	O
optional	O
bitflags	O
representing	O
the	O
current	O
volume	O
status	O
on	O
FAT16	B-Application
and	O
FAT32	B-Application
,	O
but	O
not	O
on	O
FAT12	B-Application
volumes	O
.	O
</s>
<s>
If	O
bit	O
15	O
(	O
on	O
FAT16	B-Application
)	O
or	O
bit	O
27	O
(	O
on	O
FAT32	B-Application
)	O
is	O
not	O
set	O
when	O
mounting	O
the	O
volume	O
,	O
the	O
volume	O
was	O
not	O
properly	O
unmounted	O
before	O
shutdown	O
or	O
ejection	O
and	O
thus	O
is	O
in	O
an	O
unknown	O
and	O
possibly	O
"	O
dirty	O
"	O
state	O
.	O
</s>
<s>
On	O
FAT32	B-Application
volumes	O
,	O
the	O
FS	O
Information	O
Sector	O
may	O
hold	O
outdated	O
data	O
and	O
thus	O
should	O
not	O
be	O
used	O
.	O
</s>
<s>
The	O
operating	O
system	O
would	O
then	O
typically	O
run	O
SCANDISK	O
or	O
CHKDSK	B-Device
on	O
the	O
next	O
startup	O
(	O
but	O
not	O
on	O
insertion	O
of	O
removable	O
media	O
)	O
to	O
ensure	O
and	O
possibly	O
reestablish	O
the	O
volume	O
's	O
integrity	O
.	O
</s>
<s>
If	O
bit	O
14	O
(	O
on	O
FAT16	B-Application
)	O
or	O
bit	O
26	O
(	O
on	O
FAT32	B-Application
)	O
is	O
cleared	O
,	O
the	O
operating	O
system	O
has	O
encountered	O
disk	O
I/O	O
errors	O
on	O
startup	O
,	O
a	O
possible	O
indication	O
for	O
bad	O
sectors	O
.	O
</s>
<s>
(	O
A	O
similar	O
set	O
of	O
bitflags	O
exists	O
in	O
the	O
FAT12/FAT16	O
EBPB	B-Device
at	O
offset	O
or	O
the	O
FAT32	B-Application
EBPB	B-Device
at	O
offset	O
.	O
</s>
<s>
While	O
the	O
cluster	O
1	O
entry	O
can	O
be	O
accessed	O
by	O
file	B-Application
system	I-Application
drivers	O
once	O
they	O
have	O
mounted	O
the	O
volume	O
,	O
the	O
EBPB	B-Device
entry	O
is	O
available	O
even	O
when	O
the	O
volume	O
is	O
not	O
mounted	O
and	O
thus	O
easier	O
to	O
use	O
by	O
disk	O
block	O
device	B-Application
drivers	I-Application
or	O
partitioning	O
tools	O
.	O
)	O
</s>
<s>
Some	O
non-standard	O
FAT12/FAT16	O
implementations	O
utilize	O
the	O
cluster	O
1	O
entry	O
to	O
store	O
the	O
starting	O
cluster	O
of	O
a	O
variable-sized	O
root	O
directory	B-Application
(	O
typically	O
2	O
)	O
.	O
</s>
<s>
This	O
may	O
occur	O
when	O
the	O
number	O
of	O
root	O
directory	B-Application
entries	O
in	O
the	O
BPB	O
holds	O
a	O
value	O
of	O
0	O
and	O
no	O
FAT32	B-Application
EBPB	B-Device
is	O
found	O
(	O
no	O
signature	O
or	O
at	O
offset	O
)	O
.	O
</s>
<s>
Most	O
conflicts	O
can	O
be	O
ruled	O
out	O
if	O
this	O
extension	O
is	O
only	O
allowed	O
for	O
FAT12	B-Application
with	O
less	O
than	O
and	O
FAT16	B-Application
volumes	O
with	O
less	O
than	O
clusters	O
and	O
2	O
FATs	O
.	O
</s>
<s>
The	O
first	O
data	O
cluster	O
(	O
after	O
the	O
root	O
directory	B-Application
if	O
FAT12/FAT16	O
)	O
is	O
cluster	O
2	O
,	O
marking	O
the	O
beginning	O
of	O
the	O
data	O
area	O
.	O
</s>
<s>
FAT12	B-Application
FAT16	B-Application
FAT32	B-Application
Description	O
0x000	O
0x0000	O
Free	O
Cluster	O
;	O
also	O
used	O
by	O
DOS	O
to	O
refer	O
to	O
the	O
parent	B-Application
directory	I-Application
starting	O
cluster	O
in	O
"	O
..	B-Application
"	O
entries	O
of	O
subdirectories	B-Application
of	O
the	O
root	O
directory	B-Application
on	O
FAT12/FAT16	O
volumes	O
.	O
</s>
<s>
in	O
directory	B-Application
entries	O
of	O
zero	O
length	O
or	O
deleted	O
files	O
)	O
,	O
file	B-Application
system	I-Application
implementations	O
should	O
treat	O
this	O
like	O
an	O
end-of-chain	O
marker	O
.	O
</s>
<s>
0x001	O
0x0001	O
Reserved	O
for	O
internal	O
purposes	O
;	O
MS-DOS/PC	O
DOS	O
use	O
this	O
cluster	O
value	O
as	O
a	O
temporary	O
non-free	O
cluster	O
indicator	O
while	O
constructing	O
cluster	O
chains	O
during	O
file	O
allocation	O
(	O
only	O
seen	O
on	O
disk	O
if	O
there	O
is	O
a	O
crash	O
or	O
power	O
failure	O
in	O
the	O
middle	O
of	O
this	O
process	O
)	O
.	O
</s>
<s>
If	O
this	O
value	O
occurs	O
in	O
on-disk	O
cluster	O
chains	O
,	O
file	B-Application
system	I-Application
implementations	O
should	O
treat	O
this	O
like	O
an	O
end-of-chain	O
marker	O
.	O
</s>
<s>
MS-DOS/PC	O
DOS	O
accept	O
values	O
up	O
to	O
/	O
/	O
(	O
sometimes	O
more	O
;	O
see	O
below	O
)	O
,	O
whereas	O
for	O
Atari	B-Device
GEMDOS	B-Operating_System
only	O
values	O
up	O
to	O
are	O
allowed	O
on	O
FAT16	B-Application
volumes	O
.	O
</s>
<s>
Volume	O
sizes	O
which	O
would	O
utilize	O
these	O
values	O
as	O
data	O
clusters	O
should	O
be	O
avoided	O
,	O
but	O
if	O
these	O
values	O
occur	O
in	O
existing	O
volumes	O
,	O
the	O
file	B-Application
system	I-Application
must	O
treat	O
them	O
as	O
normal	O
data	O
clusters	O
in	O
cluster-chains	O
(	O
ideally	O
applying	O
additional	O
sanity	O
checks	O
)	O
,	O
similar	O
to	O
what	O
MS-DOS	B-Application
,	O
PC	B-Operating_System
DOS	I-Operating_System
and	O
DR-DOS	B-Application
do	O
,	O
and	O
should	O
avoid	O
allocating	O
them	O
for	O
files	O
otherwise	O
.	O
</s>
<s>
MS-DOS/PC	O
DOS	O
3.3	O
and	O
higher	O
treats	O
a	O
value	O
of	O
on	O
FAT12	B-Application
(	O
but	O
not	O
on	O
FAT16	B-Application
or	O
FAT32	B-Application
)	O
volumes	O
as	O
additional	O
end-of-chain	O
marker	O
similar	O
to	O
-	O
.	O
</s>
<s>
For	O
compatibility	O
with	O
MS-DOS/PC	O
DOS	O
,	O
file	B-Application
systems	I-Application
should	O
avoid	O
to	O
use	O
data	O
cluster	O
in	O
cluster	O
chains	O
on	O
FAT12	B-Application
volumes	O
(	O
that	O
is	O
,	O
treat	O
it	O
as	O
a	O
reserved	O
cluster	O
similar	O
to	O
)	O
.	O
</s>
<s>
Corresponds	O
with	O
the	O
default	O
format	B-Application
filler	O
value	O
on	O
IBM	O
compatible	O
machines	O
.	O
)	O
</s>
<s>
Volumes	O
should	O
not	O
be	O
created	O
which	O
would	O
utilize	O
this	O
value	O
as	O
data	O
cluster	O
,	O
but	O
if	O
this	O
value	O
occurs	O
in	O
existing	O
volumes	O
,	O
the	O
file	B-Application
system	I-Application
must	O
treat	O
it	O
as	O
normal	O
data	O
cluster	O
in	O
cluster-chains	O
(	O
ideally	O
applying	O
additional	O
sanity	O
checks	O
)	O
,	O
and	O
should	O
avoid	O
to	O
allocate	O
it	O
for	O
files	O
otherwise	O
.	O
</s>
<s>
The	O
cutover	O
values	O
for	O
the	O
maximum	O
number	O
of	O
clusters	O
for	O
FAT12	B-Application
and	O
FAT16	B-Application
file	B-Application
systems	I-Application
are	O
defined	O
as	O
such	O
that	O
the	O
highest	O
possible	O
data	O
cluster	O
values	O
(	O
and	O
,	O
respectively	O
)	O
will	O
always	O
be	O
smaller	O
than	O
this	O
value	O
.	O
</s>
<s>
Therefore	O
,	O
this	O
value	O
cannot	O
normally	O
occur	O
in	O
cluster-chains	O
,	O
but	O
if	O
it	O
does	O
,	O
it	O
may	O
be	O
treated	O
as	O
a	O
normal	O
data	O
cluster	O
,	O
since	O
could	O
have	O
been	O
a	O
non-standard	O
data	O
cluster	O
on	O
FAT12	B-Application
volumes	O
before	O
the	O
introduction	O
of	O
the	O
bad	O
cluster	O
marker	O
with	O
DOS	O
2.0	O
or	O
the	O
introduction	O
of	O
FAT16	B-Application
with	O
DOS	O
3.0	O
,	O
and	O
could	O
have	O
been	O
a	O
non-standard	O
data	O
cluster	O
on	O
FAT16	B-Application
volumes	O
before	O
the	O
introduction	O
of	O
FAT32	B-Application
with	O
DOS	O
7.10	O
.	O
</s>
<s>
Theoretically	O
,	O
can	O
be	O
part	O
of	O
a	O
valid	O
cluster	O
chain	O
on	O
FAT32	B-Application
volumes	O
,	O
but	O
disk	O
utilities	O
should	O
avoid	O
creating	O
FAT32	B-Application
volumes	O
,	O
where	O
this	O
condition	O
could	O
occur	O
.	O
</s>
<s>
The	O
file	B-Application
system	I-Application
should	O
avoid	O
to	O
allocate	O
this	O
cluster	O
for	O
files	O
.	O
</s>
<s>
File	B-Application
system	I-Application
implementations	O
must	O
treat	O
all	O
these	O
values	O
as	O
end-of-chain	O
marker	O
at	O
the	O
same	O
time	O
.	O
</s>
<s>
Most	O
file	B-Application
system	I-Application
implementations	O
(	O
including	O
86-DOS	B-Operating_System
,	O
MS-DOS	B-Application
,	O
PC	B-Operating_System
DOS	I-Operating_System
and	O
DR-DOS	B-Application
)	O
use	O
/	O
/	O
as	O
end-of-file	O
marker	O
when	O
allocating	O
files	O
,	O
but	O
versions	O
of	O
Linux	O
before	O
2.5.40	O
used	O
/	O
/	O
.	O
</s>
<s>
Versions	O
of	O
mkdosfs	O
(	O
dosfstools	O
up	O
to	O
3.0.26	O
)	O
continue	O
to	O
use	O
for	O
the	O
root	O
directory	B-Application
on	O
FAT32	B-Application
volumes	O
,	O
whereas	O
some	O
disk	O
repair	O
and	O
defragment	O
tools	O
utilize	O
other	O
values	O
in	O
the	O
set	O
(	O
e.g.	O
,	O
SCANDISK	O
may	O
use	O
/	O
/	O
instead	O
)	O
.	O
</s>
<s>
While	O
in	O
the	O
original	O
8-bit	O
FAT	B-Application
implementation	I-Application
in	O
Microsoft	O
's	O
Standalone	O
Disk	O
BASIC	O
different	O
end	O
markers	O
(	O
..	B-Application
)	O
were	O
used	O
to	O
indicate	O
the	O
number	O
of	O
sectors	O
(	O
0	O
to	O
13	O
)	O
used	O
up	O
in	O
the	O
last	O
cluster	O
occupied	O
by	O
a	O
file	O
,	O
different	O
end	O
markers	O
were	O
repurposed	O
under	O
DOS	O
to	O
indicate	O
different	O
types	O
of	O
media	O
,	O
with	O
the	O
currently	O
used	O
end	O
marker	O
indicated	O
in	O
the	O
cluster	O
1	O
entry	O
,	O
however	O
,	O
this	O
concept	O
does	O
not	O
seem	O
to	O
have	O
been	O
broadly	O
utilized	O
in	O
practice	O
—	O
and	O
to	O
the	O
extent	O
that	O
in	O
some	O
scenarios	O
volumes	O
may	O
not	O
be	O
recognized	O
by	O
some	O
operating	O
systems	O
,	O
if	O
some	O
of	O
the	O
low-order	O
bits	O
of	O
the	O
value	O
stored	O
in	O
cluster	O
1	O
are	O
not	O
set	O
.	O
</s>
<s>
Also	O
,	O
some	O
faulty	O
file	B-Application
system	I-Application
implementations	O
only	O
accept	O
/	O
/	O
as	O
valid	O
end-of-chain	O
marker	O
.	O
</s>
<s>
File	B-Application
system	I-Application
implementations	O
should	O
check	O
cluster	O
values	O
in	O
cluster-chains	O
against	O
the	O
maximum	O
allowed	O
cluster	O
value	O
calculated	O
by	O
the	O
actual	O
size	O
of	O
the	O
volume	O
and	O
treat	O
higher	O
values	O
as	O
if	O
they	O
were	O
end-of-chain	O
markers	O
as	O
well	O
.	O
</s>
<s>
(	O
The	O
low	O
byte	O
of	O
the	O
cluster	O
number	O
conceptually	O
corresponds	O
with	O
the	O
FAT	O
ID	O
and	O
media	O
descriptor	O
values	O
;	O
see	O
note	O
above	O
for	O
MS-DOS/PC	O
DOS	O
special	O
usage	O
of	O
on	O
FAT12	B-Application
volumes	O
.	O
)	O
</s>
<s>
FAT32	B-Application
uses	O
28	O
bits	O
for	O
cluster	O
numbers	O
.	O
</s>
<s>
A	O
standard	O
conformant	O
FAT32	B-Application
file	B-Application
system	I-Application
driver	O
or	O
maintenance	O
tool	O
must	O
not	O
rely	O
on	O
the	O
upper	O
4	O
bits	O
to	O
be	O
zero	O
and	O
it	O
must	O
strip	O
them	O
off	O
before	O
evaluating	O
the	O
cluster	O
number	O
in	O
order	O
to	O
cope	O
with	O
possible	O
future	O
expansions	O
where	O
these	O
bits	O
may	O
be	O
used	O
for	O
other	O
purposes	O
.	O
</s>
<s>
They	O
must	O
not	O
be	O
cleared	O
by	O
the	O
file	B-Application
system	I-Application
driver	O
when	O
allocating	O
new	O
clusters	O
,	O
but	O
should	O
be	O
cleared	O
during	O
a	O
reformat	O
.	O
</s>
<s>
The	O
root	O
directory	B-Application
table	I-Application
in	O
FAT12	B-Application
and	O
FAT16	B-Application
file	B-Application
systems	I-Application
occupies	O
the	O
special	O
Root	O
Directory	B-Application
Region	O
location	O
.	O
</s>
<s>
Aside	O
from	O
the	O
root	O
directory	B-Application
table	I-Application
in	O
FAT12	B-Application
and	O
FAT16	B-Application
file	B-Application
systems	I-Application
,	O
which	O
occupies	O
the	O
special	O
Root	O
Directory	B-Application
Region	O
location	O
,	O
all	O
directory	B-Application
tables	I-Application
are	O
stored	O
in	O
the	O
data	O
region	O
.	O
</s>
<s>
The	O
actual	O
number	O
of	O
entries	O
in	O
a	O
directory	B-Application
stored	O
in	O
the	O
data	O
region	O
can	O
grow	O
by	O
adding	O
another	O
cluster	O
to	O
the	O
chain	O
in	O
the	O
FAT	O
.	O
</s>
<s>
A	O
directory	B-Application
table	I-Application
is	O
a	O
special	O
type	O
of	O
file	O
that	O
represents	O
a	O
directory	B-Application
(	O
also	O
known	O
as	O
a	O
folder	O
)	O
.	O
</s>
<s>
Since	O
86-DOS	B-Operating_System
0.42	O
,	O
each	O
file	O
or	O
(	O
since	O
MS-DOS	B-Application
1.40	O
and	O
PCDOS	B-Operating_System
2.0	O
)	O
subdirectory	B-Application
stored	O
within	O
it	O
is	O
represented	O
by	O
a	O
32-byte	O
entry	O
in	O
the	O
table	O
.	O
</s>
<s>
Each	O
entry	O
records	O
the	O
name	O
,	O
extension	O
,	O
attributes	O
(	O
archive	O
,	O
directory	B-Application
,	O
hidden	O
,	O
read-only	O
,	O
system	O
and	O
volume	O
)	O
,	O
the	O
address	O
of	O
the	O
first	O
cluster	O
of	O
the	O
file/directory	O
'	O
s	O
data	O
,	O
the	O
size	O
of	O
the	O
file/directory	O
,	O
and	O
the	O
date	O
and	O
(	O
since	O
PCDOS	B-Operating_System
1.1	O
)	O
also	O
the	O
time	O
of	O
last	O
modification	O
.	O
</s>
<s>
Earlier	O
versions	O
of	O
86-DOS	B-Operating_System
used	O
16-byte	O
directory	B-Application
entries	O
only	O
,	O
supporting	O
no	O
files	O
larger	O
than	O
16	O
MB	O
and	O
no	O
time	O
of	O
last	O
modification	O
.	O
</s>
<s>
The	O
FAT	O
file	B-Application
system	I-Application
itself	O
does	O
not	O
impose	O
any	O
limits	O
on	O
the	O
depth	O
of	O
a	O
subdirectory	B-Application
tree	O
for	O
as	O
long	O
as	O
there	O
are	O
free	O
clusters	O
available	O
to	O
allocate	O
the	O
subdirectories	B-Application
,	O
however	O
,	O
the	O
internal	O
Current	O
Directory	B-Application
Structure	O
(	O
CDS	O
)	O
under	O
MS-DOS/PCDOS	O
limits	O
the	O
absolute	O
path	O
of	O
a	O
directory	B-Application
to	O
66	O
characters	O
(	O
including	O
the	O
drive	O
letter	O
,	O
but	O
excluding	O
the	O
NUL	O
byte	O
delimiter	O
)	O
,	O
thereby	O
limiting	O
the	O
maximum	O
supported	O
depth	O
of	O
subdirectories	B-Application
to	O
32	O
,	O
whatever	O
occurs	O
earlier	O
.	O
</s>
<s>
Concurrent	B-Operating_System
DOS	I-Operating_System
,	O
MultiuserDOS	O
and	O
DRDOS3.31	O
to	O
6.0	O
(	O
up	O
to	O
including	O
the	O
1992-11	O
updates	O
)	O
do	O
not	O
store	O
absolute	O
paths	O
to	O
working	O
directories	B-Application
internally	O
and	O
therefore	O
do	O
not	O
show	O
this	O
limitation	O
.	O
</s>
<s>
The	O
same	O
applies	O
to	O
Atari	B-Device
GEMDOS	B-Operating_System
,	O
but	O
the	O
Atari	B-Device
Desktop	O
does	O
not	O
support	O
more	O
than	O
8	O
sub-directory	O
levels	O
.	O
</s>
<s>
FlexOS	B-Operating_System
,	O
4680OS	O
and	O
4690OS	O
support	O
a	O
length	O
of	O
up	O
to	O
127bytes	O
as	O
well	O
,	O
allowing	O
depths	O
down	O
to	O
60	O
levels	O
.	O
</s>
<s>
PalmDOS	B-Operating_System
,	O
DRDOS6.0	O
(	O
since	O
BDOS7.1	O
)	O
and	O
higher	O
,	O
NovellDOS	O
,	O
and	O
OpenDOS	B-Application
sport	O
a	O
MS-DOS-compatible	O
CDS	O
and	O
therefore	O
have	O
the	O
same	O
length	O
limits	O
as	O
MS-DOS/PCDOS	O
.	O
</s>
<s>
Each	O
entry	O
can	O
be	O
preceded	O
by	O
"	O
fake	O
entries	O
"	O
to	O
support	O
a	O
VFAT	B-Application
long	O
filename	O
(	O
LFN	O
)	O
;	O
see	O
further	O
below	O
.	O
</s>
<s>
Space	O
(	O
though	O
trailing	O
spaces	O
in	O
either	O
the	O
base	O
name	O
or	O
the	O
extension	O
are	O
considered	O
to	O
be	O
padding	O
and	O
not	O
a	O
part	O
of	O
the	O
file	O
name	O
;	O
also	O
filenames	O
with	O
space	O
in	O
them	O
could	O
not	O
easily	O
be	O
used	O
on	O
the	O
DOS	O
command	O
line	O
prior	O
to	O
Windows95	B-Application
because	O
of	O
the	O
lack	O
of	O
a	O
suitable	O
escaping	B-Algorithm
system	I-Algorithm
)	O
.	O
</s>
<s>
Another	O
exception	O
are	O
the	O
internal	O
commands	O
MKDIR/MD	O
and	O
RMDIR/RD	O
under	O
DR-DOS	B-Application
which	O
accept	O
single	O
arguments	O
and	O
therefore	O
allow	O
spaces	O
to	O
be	O
entered	O
.	O
</s>
<s>
This	O
excludes	O
the	O
following	O
ASCII	B-Protocol
characters	I-Protocol
:	O
</s>
<s>
The	O
following	O
additional	O
characters	O
are	O
allowed	O
on	O
Atari	B-Device
's	O
GEMDOS	B-Operating_System
,	O
but	O
should	O
be	O
avoided	O
for	O
compatibility	O
with	O
MS-DOS/PCDOS	O
:	O
</s>
<s>
The	O
semicolon	O
(	O
;	O
)	O
should	O
be	O
avoided	O
in	O
filenames	O
under	O
DRDOS	B-Application
3.31	O
and	O
higher	O
,	O
PalmDOS	B-Operating_System
,	O
NovellDOS	O
,	O
OpenDOS	B-Application
,	O
ConcurrentDOS	O
,	O
MultiuserDOS	O
,	O
SystemManager	O
and	O
REAL/32	B-Operating_System
,	O
because	O
it	O
may	O
conflict	O
with	O
the	O
syntax	O
to	O
specify	O
file	O
and	O
directory	B-Application
passwords	O
:	O
"	O
...	O
\DIRSPEC.EXT;DIRPWD\FILESPEC.EXT;FILEPWD	O
 "	O
.	O
</s>
<s>
The	O
operating	O
system	O
will	O
strip	O
off	O
one	O
(	O
and	O
also	O
twosince	O
DR-DOS	B-Application
7.02	O
)	O
semicolons	O
and	O
pending	O
passwords	O
from	O
the	O
filenames	O
before	O
storing	O
them	O
on	O
disk	O
.	O
</s>
<s>
(	O
The	O
command	O
processor	O
4DOS	B-Application
uses	O
semicolons	O
for	O
include	O
lists	O
and	O
requires	O
the	O
semicolon	O
to	O
be	O
doubled	O
for	O
password	O
protected	O
files	O
with	O
any	O
commands	O
supporting	O
wildcards	O
.	O
)	O
</s>
<s>
The	O
at-sign	O
character	O
( @	O
)	O
is	O
used	O
for	O
filelists	O
by	O
many	O
DR-DOS	B-Application
,	O
PalmDOS	B-Operating_System
,	O
Novell	B-Operating_System
DOS	I-Operating_System
,	O
OpenDOS	B-Application
and	O
Multiuser	B-Operating_System
DOS	I-Operating_System
,	O
System	O
Manager	O
and	O
REAL/32	B-Operating_System
commands	O
,	O
as	O
well	O
as	O
by	O
4DOS	B-Application
and	O
may	O
therefore	O
sometimes	O
be	O
difficult	O
to	O
use	O
in	O
filenames	O
.	O
</s>
<s>
Under	O
Multiuser	B-Operating_System
DOS	I-Operating_System
and	O
REAL/32	B-Operating_System
,	O
the	O
exclamation	O
mark	O
(	O
!	O
)	O
</s>
<s>
Before	O
Microsoft	O
added	O
support	O
for	O
long	O
filenames	O
and	O
creation/access	O
time	O
stamps	O
,	O
bytes	O
–	O
of	O
the	O
directory	B-Application
entry	O
were	O
used	O
by	O
other	O
operating	O
systems	O
to	O
store	O
additional	O
metadata	O
,	O
most	O
notably	O
the	O
operating	O
systems	O
of	O
the	O
Digital	O
Research	O
family	O
stored	O
file	O
passwords	O
,	O
access	O
rights	O
,	O
owner	O
IDs	O
,	O
and	O
file	O
deletion	O
data	O
there	O
.	O
</s>
<s>
While	O
Microsoft	O
's	O
newer	O
extensions	O
are	O
not	O
fully	O
compatible	O
with	O
these	O
extensions	O
by	O
default	O
,	O
most	O
of	O
them	O
can	O
coexist	O
in	O
third-party	O
FAT	B-Application
implementations	I-Application
(	O
at	O
least	O
on	O
FAT12	B-Application
and	O
FAT16	B-Application
volumes	O
)	O
.	O
</s>
<s>
32-byte	O
directory	B-Application
entries	O
,	O
both	O
in	O
the	O
Root	O
Directory	B-Application
Region	O
and	O
in	O
subdirectories	B-Application
,	O
are	O
of	O
the	O
following	O
format	B-Application
(	O
see	O
also	O
8.3	O
filename	O
)	O
:	O
</s>
<s>
Also	O
serves	O
as	O
an	O
end	O
marker	O
when	O
DOS	O
scans	O
a	O
directory	B-Application
table	I-Application
.	O
</s>
<s>
(	O
Since	O
MS-DOS	B-Application
1.25	O
and	O
PC	O
DOS	O
2.0	O
,	O
not	O
in	O
earlier	O
versions	O
of	O
MS-DOS	B-Application
,	O
PC	O
DOS	O
,	O
or	O
86-DOS	B-Operating_System
.	O
</s>
<s>
Under	O
DR	O
DOS	O
6.0	O
and	O
higher	O
,	O
including	O
PalmDOS	B-Operating_System
,	O
Novell	B-Operating_System
DOS	I-Operating_System
and	O
OpenDOS	B-Application
,	O
is	O
also	O
used	O
for	O
pending	O
delete	O
files	O
under	O
DELWATCH	O
.	O
</s>
<s>
or	O
"	O
..	B-Application
"	O
(	O
since	O
MS-DOS	B-Application
1.40	O
and	O
PC	O
DOS	O
2.0	O
)	O
0xE5Entry	O
has	O
been	O
previously	O
erased	O
and/or	O
is	O
available	O
.	O
</s>
<s>
The	O
value	O
was	O
chosen	O
for	O
this	O
purpose	O
in	O
86-DOS	B-Operating_System
because	O
8-inch	O
CP/M	O
floppies	B-Device
came	O
pre-formatted	O
with	O
this	O
value	O
filled	O
and	O
so	O
could	O
be	O
used	O
to	O
store	O
files	O
out	O
of	O
the	O
box	O
.	O
</s>
<s>
Versions	O
of	O
DOS	O
prior	O
to	O
5.0	O
start	O
scanning	O
directory	B-Application
tables	I-Application
from	O
the	O
top	O
of	O
the	O
directory	B-Application
table	I-Application
to	O
the	O
bottom	O
.	O
</s>
<s>
In	O
order	O
to	O
increase	O
chances	O
for	O
successful	O
file	O
undeletion	O
,	O
DOS	O
5.0	O
and	O
higher	O
will	O
remember	O
the	O
position	O
of	O
the	O
last	O
written	O
directory	B-Application
entry	O
and	O
use	O
this	O
as	O
a	O
starting	O
point	O
for	O
directory	B-Application
table	I-Application
scans	O
.	O
</s>
<s>
Deliberately	O
setting	O
this	O
bit	O
for	O
files	O
which	O
will	O
not	O
be	O
written	O
to	O
(	O
executables	O
,	O
shared	O
libraries	O
and	O
data	O
files	O
)	O
may	O
help	O
avoid	O
problems	O
with	O
concurrent	O
file	B-Application
access	I-Application
in	O
multi-tasking	O
,	O
multi-user	O
or	O
network	O
environments	O
with	O
applications	O
not	O
specifically	O
designed	O
to	O
work	O
in	O
such	O
environments	O
(	O
i.e.	O
</s>
<s>
The	O
DCF	B-Algorithm
digital	O
camera	B-Algorithm
file	I-Algorithm
system	I-Algorithm
standard	O
utilizes	O
the	O
Read	O
Only	O
attribute	O
to	O
allow	O
directories	B-Application
or	O
individual	O
files	O
(	O
DCF	B-Algorithm
objects	O
)	O
to	O
be	O
marked	O
as	O
"	O
protected	O
"	O
from	O
deletion	O
by	O
the	O
user.10x02Hidden	O
.	O
</s>
<s>
Hides	O
files	O
or	O
directories	B-Application
from	O
normal	O
directory	B-Application
views	O
.	O
</s>
<s>
Under	O
DR	O
DOS	O
3.31	O
and	O
higher	O
,	O
under	O
PalmDOS	B-Operating_System
,	O
Novell	O
DOS	O
,	O
OpenDOS	B-Application
,	O
Concurrent	O
DOS	O
,	O
Multiuser	O
DOS	O
,	O
REAL/32	B-Operating_System
,	O
password	O
protected	O
files	O
and	O
directories	B-Application
also	O
have	O
the	O
hidden	O
attribute	O
set	O
.	O
</s>
<s>
Password-aware	O
operating	O
systems	O
should	O
not	O
hide	O
password-protected	O
files	O
from	O
directory	B-Application
views	O
,	O
even	O
if	O
this	O
bit	O
may	O
be	O
set	O
.	O
</s>
<s>
The	O
password	O
protection	O
mechanism	O
does	O
not	O
depend	O
on	O
the	O
hidden	O
attribute	O
being	O
set	O
up	O
to	O
including	O
DR-DOS	B-Application
7.03	O
,	O
but	O
if	O
the	O
hidden	O
attribute	O
is	O
set	O
,	O
it	O
should	O
not	O
be	O
cleared	O
for	O
any	O
password-protected	O
files.20x04System	O
.	O
</s>
<s>
Indicates	O
that	O
the	O
file	O
belongs	O
to	O
the	O
system	O
and	O
must	O
not	O
be	O
physically	O
moved	O
(	O
e.g.	O
,	O
during	O
defragmentation	O
)	O
,	O
because	O
there	O
may	O
be	O
references	O
into	O
the	O
file	O
using	O
absolute	O
addressing	O
bypassing	O
the	O
file	B-Application
system	I-Application
(	O
boot	B-Application
loaders	I-Application
,	O
kernel	O
images	O
,	O
swap	O
files	O
,	O
extended	B-Application
attributes	I-Application
,	O
etc	O
.	O
</s>
<s>
(	O
Since	O
MS-DOS	B-Application
1.28	O
and	O
PC	O
DOS	O
2.0	O
)	O
Indicates	O
an	O
optional	O
directory	B-Application
volume	O
label	O
,	O
normally	O
only	O
residing	O
in	O
a	O
volume	O
's	O
root	O
directory	B-Application
.	O
</s>
<s>
Ideally	O
,	O
the	O
volume	O
label	O
should	O
be	O
the	O
first	O
entry	O
in	O
the	O
directory	B-Application
(	O
after	O
reserved	O
entries	O
)	O
in	O
order	O
to	O
avoid	O
problems	O
with	O
VFAT	B-Application
LFNs	O
.	O
</s>
<s>
If	O
this	O
volume	O
label	O
is	O
not	O
present	O
,	O
some	O
systems	O
may	O
fall	O
back	O
to	O
display	O
the	O
partition	O
volume	O
label	O
instead	O
,	O
if	O
an	O
EBPB	B-Device
is	O
present	O
in	O
the	O
boot	B-Device
sector	I-Device
(	O
not	O
present	O
with	O
some	O
non-bootable	O
block	O
device	B-Application
drivers	I-Application
,	O
and	O
possibly	O
not	O
writeable	O
with	O
boot	B-Device
sector	I-Device
write	O
protection	O
)	O
.	O
</s>
<s>
Even	O
if	O
this	O
volume	O
label	O
is	O
present	O
,	O
partitioning	O
tools	O
like	O
FDISK	B-Application
may	O
display	O
the	O
partition	O
volume	O
label	O
instead	O
.	O
</s>
<s>
The	O
entry	O
occupies	O
a	O
directory	B-Application
entry	O
but	O
has	O
no	O
file	O
associated	O
with	O
it	O
.	O
</s>
<s>
Pending	O
delete	O
files	O
and	O
directories	B-Application
under	O
DELWATCH	O
have	O
the	O
volume	O
attribute	O
set	O
until	O
they	O
are	O
purged	O
or	O
undeleted.40x10Subdirectory	O
.	O
</s>
<s>
(	O
Since	O
MS-DOS	B-Application
1.40	O
and	O
PC	O
DOS	O
2.0	O
)	O
Indicates	O
that	O
the	O
cluster-chain	O
associated	O
with	O
this	O
entry	O
gets	O
interpreted	O
as	O
subdirectory	B-Application
instead	O
of	O
as	O
a	O
file	O
.	O
</s>
<s>
Subdirectories	B-Application
have	O
a	O
filesize	O
entry	O
of	O
zero.50x20Archive	O
.	O
</s>
<s>
(	O
Since	O
DOS	O
2.0	O
)	O
Typically	O
set	O
by	O
the	O
operating	O
system	O
as	O
soon	O
as	O
the	O
file	O
is	O
created	O
or	O
modified	O
to	O
mark	O
the	O
file	O
as	O
"	O
dirty	O
"	O
,	O
and	O
reset	O
by	O
backup	O
software	O
once	O
the	O
file	O
has	O
been	O
backed	O
up	O
to	O
indicate	O
"	O
pure	O
"	O
state.60x40Device	O
(	O
internally	O
set	O
for	O
character	O
device	B-Application
names	I-Application
found	O
in	O
filespecs	O
,	O
never	O
found	O
on	O
disk	O
)	O
,	O
must	O
not	O
be	O
changed	O
by	O
disk	O
tools.70x80Reserved	O
,	O
must	O
not	O
be	O
changed	O
by	O
disk	O
tools	O
.	O
</s>
<s>
Under	O
DR	O
DOS	O
6.0	O
and	O
higher	O
,	O
including	O
PalmDOS	B-Operating_System
,	O
Novell	O
DOS	O
and	O
OpenDOS	B-Application
,	O
the	O
volume	O
attribute	O
is	O
set	O
for	O
pending	O
delete	O
files	O
and	O
directories	B-Application
under	O
DELWATCH	O
.	O
</s>
<s>
An	O
attribute	O
combination	O
of	O
is	O
used	O
to	O
designate	O
a	O
VFAT	B-Application
long	O
file	O
name	O
entry	O
since	O
MS-DOS	B-Application
7.0	O
.	O
</s>
<s>
Older	O
versions	O
of	O
DOS	O
can	O
mistake	O
this	O
for	O
a	O
directory	B-Application
volume	O
label	O
,	O
as	O
they	O
take	O
the	O
first	O
entry	O
with	O
volume	O
attribute	O
set	O
as	O
volume	O
label	O
.	O
</s>
<s>
This	O
problem	O
can	O
be	O
avoided	O
if	O
a	O
directory	B-Application
volume	O
label	O
is	O
enforced	O
as	O
part	O
of	O
the	O
format	B-Application
process	O
;	O
for	O
this	O
reason	O
some	O
disk	O
tools	O
explicitly	O
write	O
dummy	O
"	O
NO␠NAME␠␠␠␠	O
"	O
directory	B-Application
volume	O
labels	O
when	O
the	O
user	O
does	O
not	O
specify	O
a	O
volume	O
label	O
.	O
</s>
<s>
Since	O
volume	O
labels	O
normally	O
do	O
n't	O
have	O
the	O
system	O
attribute	O
set	O
at	O
the	O
same	O
time	O
,	O
it	O
is	O
possible	O
to	O
distinguish	O
between	O
volume	O
labels	O
and	O
VFAT	B-Application
LFN	O
entries	O
.	O
</s>
<s>
The	O
attribute	O
combination	O
could	O
occasionally	O
also	O
occur	O
as	O
part	O
of	O
a	O
valid	O
pending	O
delete	O
file	O
under	O
DELWATCH	O
,	O
however	O
on	O
FAT12	B-Application
and	O
FAT16	B-Application
volumes	O
,	O
VFAT	B-Application
LFN	O
entries	O
always	O
have	O
the	O
cluster	O
value	O
at	O
set	O
to	O
and	O
the	O
length	O
entry	O
at	O
is	O
never	O
,	O
whereas	O
the	O
entry	O
at	O
is	O
always	O
non-zero	O
for	O
pending	O
delete	O
files	O
under	O
DELWATCH	O
.	O
</s>
<s>
This	O
check	O
does	O
not	O
work	O
on	O
FAT32	B-Application
volumes	O
.	O
</s>
<s>
CP/M	B-Operating_System
-86	I-Operating_System
and	O
DOS	O
Plus	O
store	O
user	O
attributes	O
F1'—F4'	O
here	O
.	O
</s>
<s>
(	O
DOS	O
Plus	O
1.2	O
with	O
BDOS	O
4.1	O
supports	O
passwords	O
only	O
on	O
CP/M	O
media	O
,	O
not	O
on	O
FAT12	B-Application
or	O
FAT16	B-Application
media	O
.	O
</s>
<s>
While	O
DOS	O
Plus	O
2.1	O
supported	O
logical	B-Application
sectored	I-Application
FATs	I-Application
with	O
a	O
partition	B-Application
type	I-Application
,	O
FAT16B	O
and	O
FAT32	B-Application
volumes	O
were	O
not	O
supported	O
by	O
these	O
operation	O
systems	O
.	O
</s>
<s>
Therefore	O
,	O
this	O
usage	O
does	O
not	O
conflict	O
with	O
FAT32.IFS	O
,	O
FAT16+	O
or	O
FAT32+	O
as	O
they	O
can	O
never	O
occur	O
on	O
the	O
same	O
type	O
of	O
volume	O
.	O
</s>
<s>
MSX-DOS	B-Operating_System
2	O
:	O
For	O
a	O
deleted	O
file	O
,	O
the	O
original	O
first	O
character	O
of	O
the	O
filename	O
.	O
</s>
<s>
For	O
the	O
same	O
feature	O
in	O
various	O
other	O
operating	O
systems	O
,	O
see	O
offset	O
if	O
enabled	O
in	O
MSX	O
boot	B-Device
sectors	I-Device
at	O
sector	O
offset	O
.	O
</s>
<s>
MSX-DOS	B-Operating_System
supported	O
FAT12	B-Application
volumes	O
only	O
,	O
but	O
third-party	O
extensions	O
for	O
FAT16	B-Application
volumes	O
exist	O
.	O
</s>
<s>
Therefore	O
,	O
this	O
usage	O
does	O
not	O
conflict	O
with	O
FAT32.IFS	O
and	O
FAT32+	O
below	O
.	O
</s>
<s>
It	O
does	O
not	O
conflict	O
with	O
the	O
usage	O
for	O
user	O
attributes	O
under	O
CP/M	B-Operating_System
-86	I-Operating_System
and	O
DOS	B-Operating_System
Plus	I-Operating_System
as	O
well	O
,	O
since	O
they	O
are	O
no	O
longer	O
important	O
for	O
deleted	O
files	O
.	O
</s>
<s>
Windows	B-Device
NT	I-Device
and	O
later	O
versions	O
uses	O
bits	O
3	O
and	O
4	O
to	O
encode	O
case	O
information	O
(	O
see	O
VFAT	B-Application
)	O
;	O
otherwise	O
0	O
.	O
</s>
<s>
DR-DOS	B-Application
7.0x	O
reserved	O
bits	O
other	O
than	O
3	O
and	O
4	O
for	O
internal	O
purposes	O
since	O
1997	O
.	O
</s>
<s>
On	O
FAT32	B-Application
volumes	O
under	O
OS/2	B-Application
and	O
eComStation	O
the	O
third-party	O
FAT32.IFS	O
driver	O
utilizes	O
this	O
entry	O
as	O
a	O
mark	O
byte	O
to	O
indicate	O
the	O
presence	O
of	O
extra	O
"	O
␠	O
EA.	O
␠SF	O
"	O
files	O
holding	O
extended	B-Application
attributes	I-Application
with	O
parameter	O
/EAS	O
.	O
</s>
<s>
Version	O
0.70	O
to	O
0.96	O
used	O
the	O
magic	O
values	O
(	O
no	O
EAs	B-Application
)	O
,	O
(	O
normal	O
EAs	B-Application
)	O
and	O
(	O
critical	O
EAs	B-Application
)	O
,	O
whereas	O
version	O
0.97	O
and	O
higher	O
since	O
2003-09	O
use	O
,	O
(	O
normal	O
EAs	B-Application
)	O
and	O
(	O
critical	O
EAs	B-Application
)	O
as	O
bitflags	O
for	O
compatibility	O
with	O
Windows	B-Device
NT	I-Device
.	O
</s>
<s>
First	O
character	O
of	O
a	O
deleted	O
file	O
under	O
Novell	B-Operating_System
DOS	I-Operating_System
,	O
OpenDOS	B-Application
and	O
DR-DOS	B-Application
7.02	O
and	O
higher	O
.	O
</s>
<s>
S/DOS	B-Operating_System
1	O
and	O
PTS-DOS	B-Operating_System
6.51	O
and	O
higher	O
also	O
support	O
this	O
feature	O
if	O
enabled	O
with	O
SAVENAME	B-Device
=	O
ON	O
in	O
CONFIG.SYS	O
.	O
</s>
<s>
For	O
the	O
same	O
feature	O
in	O
MSX-DOS	B-Operating_System
,	O
see	O
offset	O
.	O
</s>
<s>
Create	O
time	O
,	O
fine	O
resolution	O
:	O
10	O
ms	O
units	O
,	O
values	O
from	O
0	O
to	O
199	O
(	O
since	O
DOS	O
7.0	O
with	O
VFAT	B-Application
)	O
.	O
</s>
<s>
Under	O
DR	O
DOS	O
3.31	O
and	O
higher	O
including	O
PalmDOS	B-Operating_System
,	O
Novell	O
DOS	O
and	O
OpenDOS	B-Application
as	O
well	O
as	O
under	O
Concurrent	O
DOS	O
,	O
Multiuser	O
DOS	O
,	O
System	O
Manager	O
,	O
and	O
REAL/32	B-Operating_System
and	O
possibly	O
also	O
under	O
FlexOS	B-Operating_System
,	O
4680	O
OS	O
,	O
4690	O
OS	O
any	O
non-zero	O
value	O
indicates	O
the	O
password	O
hash	O
of	O
a	O
protected	O
file	O
,	O
directory	B-Application
or	O
volume	O
label	O
.	O
</s>
<s>
Create	O
time	O
(	O
since	O
DOS	O
7.0	O
with	O
VFAT	B-Application
)	O
.	O
</s>
<s>
If	O
bits	O
15-11	O
>	O
23	O
or	O
bits	O
10-5	O
>	O
59	O
or	O
bits	O
4-0	O
>	O
29	O
here	O
,	O
or	O
when	O
bits	O
12-0	O
at	O
offset	O
hold	O
an	O
access	O
bitmap	O
and	O
this	O
is	O
not	O
a	O
FAT32	B-Application
volume	O
or	O
a	O
volume	O
using	O
OS/2	B-Application
Extended	B-Application
Attributes	I-Application
,	O
then	O
this	O
entry	O
actually	O
holds	O
a	O
password	O
hash	O
,	O
otherwise	O
it	O
can	O
be	O
assumed	O
to	O
be	O
a	O
file	O
creation	O
time	O
.	O
</s>
<s>
FlexOS	B-Operating_System
,	O
4680	O
OS	O
and	O
4690	O
OS	O
store	O
a	O
record	O
size	O
in	O
the	O
word	O
at	O
entry	O
.	O
</s>
<s>
This	O
is	O
mainly	O
used	O
for	O
their	O
special	O
database-like	O
file	O
types	O
random	O
file	O
,	O
direct	O
file	O
,	O
keyed	O
file	O
,	O
and	O
sequential	B-Application
file	I-Application
.	O
</s>
<s>
With	O
DELWATCH	O
2.00	O
and	O
higher	O
under	O
Novell	B-Operating_System
DOS	I-Operating_System
7	O
,	O
OpenDOS	B-Application
7.01	O
and	O
DR-DOS	B-Application
7.02	O
and	O
higher	O
,	O
this	O
entry	O
is	O
used	O
to	O
store	O
the	O
last	O
modified	O
time	O
stamp	O
for	O
pending	O
delete	O
files	O
and	O
directories	B-Application
.	O
</s>
<s>
See	O
offset	O
for	O
a	O
format	B-Application
description	O
.	O
</s>
<s>
Create	O
date	O
(	O
since	O
DOS	O
7.0	O
with	O
VFAT	B-Application
)	O
.	O
</s>
<s>
Creation	O
dates	O
and	O
record	O
sizes	O
cannot	O
be	O
used	O
at	O
the	O
same	O
time	O
,	O
however	O
,	O
both	O
are	O
stored	O
only	O
on	O
file	O
creation	O
and	O
never	O
changed	O
later	O
on	O
,	O
thereby	O
limiting	O
the	O
conflict	O
to	O
FlexOS	B-Operating_System
,	O
4680	O
OS	O
and	O
4690	B-Language
OS	I-Language
systems	O
accessing	O
files	O
created	O
under	O
foreign	O
operating	O
systems	O
as	O
well	O
as	O
potential	O
display	O
or	O
file	O
sorting	O
problems	O
on	O
systems	O
trying	O
to	O
interpret	O
a	O
record	O
size	O
as	O
creation	O
time	O
.	O
</s>
<s>
FlexOS	B-Operating_System
,	O
4680	O
OS	O
,	O
4690	O
OS	O
,	O
Multiuser	B-Operating_System
DOS	I-Operating_System
,	O
System	O
Manager	O
,	O
REAL/32	B-Operating_System
and	O
DR	O
DOS	O
6.0	O
and	O
higher	O
with	O
multi-user	O
security	O
enabled	O
use	O
this	O
field	O
to	O
store	O
owner	O
IDs	O
.	O
</s>
<s>
With	O
DELWATCH	O
2.00	O
and	O
higher	O
under	O
Novell	O
DOS	O
7	O
,	O
OpenDOS	B-Application
7.01	O
and	O
DR-DOS	B-Application
7.02	O
and	O
higher	O
,	O
this	O
entry	O
is	O
used	O
to	O
store	O
the	O
last	O
modified	O
date	O
stamp	O
for	O
pending	O
delete	O
files	O
and	O
directories	B-Application
.	O
</s>
<s>
See	O
offset	O
for	O
a	O
format	B-Application
description	O
.	O
</s>
<s>
Last	O
access	O
date	O
(	O
since	O
DOS	O
7.0	O
if	O
ACCDATE	B-Device
enabled	O
in	O
CONFIG.SYS	O
for	O
the	O
corresponding	O
drive	O
)	O
;	O
see	O
offset	O
for	O
a	O
format	B-Application
description	O
.	O
</s>
<s>
High	O
two	O
bytes	O
of	O
first	O
cluster	O
number	O
in	O
FAT32	B-Application
;	O
with	O
the	O
low	O
two	O
bytes	O
stored	O
at	O
offset	O
.	O
</s>
<s>
Access	O
rights	O
bitmap	O
for	O
world/group/owner	O
read/write/execute/delete	O
protection	O
for	O
password	O
protected	O
files	O
,	O
directories	B-Application
(	O
or	O
volume	O
labels	O
)	O
under	O
DR	O
DOS	O
3.31	O
and	O
higher	O
,	O
including	O
PalmDOS	B-Operating_System
,	O
Novell	O
DOS	O
and	O
OpenDOS	B-Application
,	O
and	O
under	O
FlexOS	B-Operating_System
,	O
4680	O
OS	O
,	O
4690	O
OS	O
,	O
Concurrent	O
DOS	O
,	O
Multiuser	O
DOS	O
,	O
System	O
Manager	O
,	O
and	O
REAL/32	B-Operating_System
.	O
</s>
<s>
Typical	O
values	O
stored	O
on	O
a	O
single-user	O
system	O
are	O
(	O
PASSWORD	O
/N	O
for	O
all	O
access	O
rights	O
"	O
RWED	O
"	O
)	O
,	O
(	O
PASSWORD	O
/D	O
for	O
access	O
rights	O
"	O
RW	O
?	O
-	O
"	O
)	O
,	O
(	O
PASSWORD	O
/W	O
for	O
access	O
rights	O
"	O
R-	O
?	O
-	O
"	O
)	O
and	O
(	O
PASSWORD	O
/R	O
for	O
files	O
or	O
PASSWORD	O
/P	O
for	O
directories	B-Application
for	O
access	O
rights	O
"	O
--?-	O
 "	O
)	O
.	O
</s>
<s>
If	O
execute	O
bits	O
are	O
set	O
on	O
systems	O
other	O
than	O
FlexOS	B-Operating_System
,	O
4680	O
OS	O
or	O
4690	O
OS	O
,	O
they	O
will	O
be	O
treated	O
similar	O
to	O
read	O
bits	O
.	O
</s>
<s>
Single-user	O
systems	O
calculate	O
the	O
most	O
restrictive	O
rights	O
of	O
the	O
three	O
sets	O
(	O
DR	O
DOS	O
up	O
to	O
5.0	O
used	O
bits	O
0-3	O
only	O
)	O
and	O
check	O
if	O
any	O
of	O
the	O
requested	O
file	B-Application
access	I-Application
types	O
requires	O
a	O
permission	O
and	O
if	O
a	O
file	O
password	O
is	O
stored	O
.	O
</s>
<s>
If	O
not	O
,	O
file	B-Application
access	I-Application
is	O
granted	O
.	O
</s>
<s>
Otherwise	O
the	O
stored	O
password	O
is	O
checked	O
against	O
an	O
optional	O
global	O
password	O
provided	O
by	O
the	O
operating	O
system	O
and	O
an	O
optional	O
file	O
password	O
provided	O
as	O
part	O
of	O
the	O
filename	O
separated	O
by	O
a	O
semicolon	O
(	O
not	O
under	O
FlexOS	B-Operating_System
,	O
4680	O
OS	O
,	O
4690	O
OS	O
)	O
.	O
</s>
<s>
Under	O
FlexOS	B-Operating_System
,	O
4680	O
OS	O
and	O
4690	O
OS	O
the	O
system	O
assigns	O
group	O
and	O
user	O
IDs	O
to	O
applications	O
when	O
launched	O
.	O
</s>
<s>
When	O
they	O
request	O
file	B-Application
access	I-Application
,	O
their	O
group	O
and	O
user	O
IDs	O
are	O
compared	O
with	O
the	O
group	O
and	O
user	O
IDs	O
of	O
the	O
file	O
to	O
be	O
opened	O
.	O
</s>
<s>
Once	O
the	O
permission	O
class	O
has	O
been	O
determined	O
,	O
the	O
operating	O
system	O
will	O
check	O
if	O
any	O
of	O
the	O
access	O
types	O
of	O
the	O
requested	O
file	O
operation	O
requires	O
a	O
permission	O
according	O
to	O
the	O
stored	O
bitflags	O
of	O
the	O
selected	O
class	O
owner	O
,	O
group	O
or	O
world	O
in	O
the	O
file	O
's	O
directory	B-Application
entry	O
.	O
</s>
<s>
If	O
multiuser	O
file	O
/	O
directory	B-Application
password	O
security	O
is	O
enabled	O
the	O
system	O
will	O
not	O
fail	O
at	O
this	O
stage	O
but	O
perform	O
the	O
password	O
checking	O
mechanism	O
for	O
the	O
selected	O
permission	O
class	O
similar	O
to	O
the	O
procedure	O
described	O
above	O
.	O
</s>
<s>
With	O
multi-user	O
security	O
loaded	O
many	O
utilities	O
since	O
DR	B-Application
DOS	I-Application
6.0	O
will	O
provide	O
an	O
additional	O
/U:name	O
parameter	O
.	O
</s>
<s>
File	B-Application
access	I-Application
rights	O
bitmap	O
:	O
</s>
<s>
Extended	B-Application
Attributes	I-Application
handle	O
(	O
used	O
by	O
OS/2	B-Application
1.2	O
and	O
higher	O
as	O
well	O
as	O
by	O
Windows	B-Device
NT	I-Device
)	O
in	O
FAT12	B-Application
and	O
FAT16	B-Application
;	O
first	O
cluster	O
of	O
EA	O
file	O
or	O
0	O
,	O
if	O
not	O
used	O
.	O
</s>
<s>
A	O
different	O
method	O
to	O
store	O
extended	B-Application
attributes	I-Application
has	O
been	O
devised	O
for	O
FAT32	B-Application
volumes	O
,	O
see	O
FAT32.IFS	O
under	O
offset	O
.	O
</s>
<s>
The	O
storage	O
of	O
the	O
high	O
two	O
bytes	O
of	O
the	O
first	O
cluster	O
in	O
a	O
file	O
on	O
FAT32	B-Application
partially	O
conflicts	O
with	O
access	O
rights	O
bitmaps	O
.	O
</s>
<s>
Last	O
modified	O
time	O
(	O
since	O
PC	O
DOS	O
1.1/MS	O
-DOS	O
1.20	O
)	O
;	O
see	O
offset	O
for	O
a	O
format	B-Application
description	O
.	O
</s>
<s>
Under	O
Novell	O
DOS	O
,	O
OpenDOS	B-Application
and	O
DR-DOS	B-Application
7.02	O
and	O
higher	O
,	O
this	O
entry	O
holds	O
the	O
deletion	O
time	O
of	O
pending	O
delete	O
files	O
or	O
directories	B-Application
under	O
DELWATCH	O
2.00	O
or	O
higher	O
.	O
</s>
<s>
See	O
offset	O
for	O
a	O
format	B-Application
description	O
.	O
</s>
<s>
Last	O
modified	O
date	O
;	O
see	O
offset	O
for	O
a	O
format	B-Application
description	O
.	O
</s>
<s>
Under	O
Novell	O
DOS	O
,	O
OpenDOS	B-Application
and	O
DR-DOS	B-Application
7.02	O
and	O
higher	O
,	O
this	O
entry	O
holds	O
the	O
deletion	O
date	O
of	O
pending	O
delete	O
files	O
or	O
directories	B-Application
under	O
DELWATCH	O
2.00	O
or	O
higher	O
.	O
</s>
<s>
See	O
offset	O
for	O
a	O
format	B-Application
description	O
.	O
</s>
<s>
0x1A	O
2	O
Start	O
of	O
file	O
in	O
clusters	O
in	O
FAT12	B-Application
and	O
FAT16	B-Application
.	O
</s>
<s>
Low	O
two	O
bytes	O
of	O
first	O
cluster	O
in	O
FAT32	B-Application
;	O
with	O
the	O
high	O
two	O
bytes	O
stored	O
at	O
offset	O
.	O
</s>
<s>
Entries	O
with	O
the	O
Volume	O
Label	O
flag	O
,	O
subdirectory	B-Application
"	O
..	B-Application
"	O
pointing	O
to	O
the	O
FAT12	B-Application
and	O
FAT16	B-Application
root	O
,	O
and	O
empty	O
files	O
with	O
size	O
0	O
should	O
have	O
first	O
cluster	O
0	O
.	O
</s>
<s>
VFAT	B-Application
LFN	O
entries	O
also	O
have	O
this	O
entry	O
set	O
to	O
0	O
;	O
on	O
FAT12	B-Application
and	O
FAT16	B-Application
volumes	O
this	O
can	O
be	O
used	O
as	O
part	O
of	O
a	O
detection	O
mechanism	O
to	O
distinguish	O
between	O
pending	O
delete	O
files	O
under	O
DELWATCH	O
and	O
VFAT	B-Application
LFNs	O
;	O
see	O
above	O
.	O
</s>
<s>
Entries	O
with	O
the	O
Volume	O
Label	O
or	O
Subdirectory	B-Application
flag	O
set	O
should	O
have	O
a	O
size	O
of	O
0	O
.	O
</s>
<s>
VFAT	B-Application
LFN	O
entries	O
never	O
store	O
the	O
value	O
here	O
.	O
</s>
<s>
This	O
can	O
be	O
used	O
as	O
part	O
of	O
a	O
detection	O
mechanism	O
to	O
distinguish	O
between	O
pending	O
delete	O
files	O
under	O
DELWATCH	O
and	O
VFAT	B-Application
LFNs	O
;	O
see	O
above	O
.	O
</s>
<s>
The	O
FlexOS-based	O
operating	O
systems	O
IBM	B-Language
4680	I-Language
OS	I-Language
and	O
IBM	B-Language
4690	I-Language
OS	I-Language
support	O
unique	O
distribution	O
attributes	O
stored	O
in	O
some	O
bits	O
of	O
the	O
previously	O
reserved	O
areas	O
in	O
the	O
directory	B-Application
entries	O
:	O
</s>
<s>
The	O
FAT12	B-Application
,	O
FAT16	B-Application
,	O
FAT16B	O
,	O
and	O
FAT32	B-Application
variants	O
of	O
the	O
FAT	O
file	B-Application
systems	I-Application
have	O
clear	O
limits	O
based	O
on	O
the	O
number	O
of	O
clusters	O
and	O
the	O
number	O
of	O
sectors	O
per	O
cluster	O
(	O
1	O
,	O
2	O
,	O
4	O
,	O
...	O
,	O
128	O
)	O
.	O
</s>
<s>
Legend	O
:	O
268435444+3	O
is	O
,	O
because	O
FAT32	B-Application
version	O
0	O
uses	O
only	O
28	O
bits	O
in	O
the	O
32-bit	O
cluster	O
numbers	O
,	O
cluster	O
numbers	O
up	O
to	O
flag	O
bad	O
clusters	O
or	O
the	O
end	O
of	O
a	O
file	O
,	O
cluster	O
number	O
0	O
flags	O
a	O
free	O
cluster	O
,	O
and	O
cluster	O
number	O
1	O
is	O
not	O
used	O
.	O
</s>
<s>
Likewise	O
65524+3	O
is	O
for	O
FAT16	B-Application
,	O
and	O
4084+3	O
is	O
for	O
FAT12	B-Application
.	O
</s>
<s>
Lines	O
in	O
square	O
brackets	O
indicate	O
the	O
unusual	O
cluster	O
size	O
128	O
,	O
and	O
for	O
FAT32	B-Application
the	O
bigger	O
than	O
necessary	O
cluster	O
sizes	O
32	O
or	O
64	O
.	O
</s>
<s>
Because	O
each	O
FAT32	B-Application
entry	O
occupies	O
32	O
bits	O
(	O
4	O
bytes	O
)	O
the	O
maximal	O
number	O
of	O
clusters	O
(	O
268435444	O
)	O
requires	O
2097152	O
FAT	O
sectors	O
for	O
a	O
sector	O
size	O
of	O
512	O
bytes	O
.	O
</s>
<s>
Therefore	O
,	O
FAT32	B-Application
introduced	O
a	O
new	O
32-bit	O
value	O
in	O
the	O
FAT32	B-Application
boot	B-Device
sector	I-Device
immediately	O
following	O
the	O
32-bit	O
value	O
for	O
the	O
total	O
number	O
of	O
sectors	O
introduced	O
in	O
the	O
FAT16B	O
variant	O
.	O
</s>
<s>
The	O
boot	B-Device
record	I-Device
extensions	O
introduced	O
with	O
DOS	O
4.0	O
start	O
with	O
a	O
magic	O
40	O
(	O
)	O
or	O
41	O
(	O
)	O
.	O
</s>
<s>
Typically	O
FAT	O
drivers	O
look	O
only	O
at	O
the	O
number	O
of	O
clusters	O
to	O
distinguish	O
FAT12	B-Application
,	O
FAT16	B-Application
,	O
and	O
FAT32	B-Application
:	O
the	O
human	O
readable	O
strings	O
identifying	O
the	O
FAT	O
variant	O
in	O
the	O
boot	B-Device
record	I-Device
are	O
ignored	O
,	O
because	O
they	O
exist	O
only	O
for	O
media	O
formatted	O
with	O
DOS	O
4.0	O
or	O
later	O
.	O
</s>
<s>
Determining	O
the	O
number	O
of	O
directory	B-Application
entries	O
per	O
cluster	O
is	O
straightforward	O
.	O
</s>
<s>
The	O
DOS	O
5	O
RMDIR/RD	O
command	O
removes	O
the	O
initial	O
"	O
.	O
"	O
</s>
<s>
(	O
this	O
directory	B-Application
)	O
and	O
"	O
..	B-Application
"	O
(	O
parent	B-Application
directory	I-Application
)	O
entries	O
in	O
subdirectories	B-Application
directly	O
,	O
therefore	O
sector	O
size	O
32	O
on	O
a	O
RAM	B-Application
disk	I-Application
is	O
possible	O
for	O
FAT12	B-Application
,	O
but	O
requires	O
2	O
or	O
more	O
sectors	O
per	O
cluster	O
.	O
</s>
<s>
A	O
FAT12	B-Application
boot	B-Device
sector	I-Device
without	O
the	O
DOS	O
4	O
extensions	O
needs	O
29	O
bytes	O
before	O
the	O
first	O
unnecessary	O
FAT16B	O
32-bit	O
number	O
of	O
hidden	O
sectors	O
,	O
this	O
leaves	O
three	O
bytes	O
for	O
the	O
(	O
on	O
a	O
RAM	B-Application
disk	I-Application
unused	O
)	O
boot	O
code	O
and	O
the	O
magic	O
at	O
the	O
end	O
of	O
all	O
boot	B-Device
sectors	I-Device
.	O
</s>
<s>
On	O
Windows	B-Device
NT	I-Device
the	O
smallest	O
supported	O
sector	O
size	O
is	O
128	O
.	O
</s>
<s>
On	O
Windows	B-Device
NT	I-Device
operating	O
systems	O
the	O
FORMAT	B-Application
command	O
options	O
/A:128K	O
and	O
/A:256K	O
correspond	O
to	O
the	O
maximal	O
cluster	O
size	O
0x80	O
(	O
128	O
)	O
with	O
a	O
sector	O
size	O
1024	O
and	O
2048	O
,	O
respectively	O
.	O
</s>
<s>
Both	O
editions	O
of	O
each	O
ECMA-107	O
and	O
ISO/IEC	O
9293	O
specify	O
a	O
Max	O
Cluster	O
Number	O
MAX	O
determined	O
by	O
the	O
formula	O
MAX	O
=	O
1+	O
trunc((TS-SSA )	O
/SC	O
)	O
,	O
and	O
reserve	O
cluster	O
numbers	O
MAX+1	O
up	O
to	O
4086	O
(	O
,	O
FAT12	B-Application
)	O
and	O
later	O
65526	O
(	O
,	O
FAT16	B-Application
)	O
for	O
future	O
standardization	O
.	O
</s>
<s>
Microsoft	O
's	O
EFI	O
FAT32	B-Application
specification	I-Application
states	O
that	O
any	O
FAT	O
file	B-Application
system	I-Application
with	O
less	O
than	O
4085	O
clusters	O
is	O
FAT12	B-Application
,	O
else	O
any	O
FAT	O
file	B-Application
system	I-Application
with	O
less	O
than	O
65,525	O
clusters	O
is	O
FAT16	B-Application
,	O
and	O
otherwise	O
it	O
is	O
FAT32	B-Application
.	O
</s>
<s>
The	O
entries	O
for	O
cluster	O
numbers	O
0	O
and	O
1	O
end	O
at	O
a	O
byte	O
boundary	O
even	O
for	O
FAT12	B-Application
,	O
e.g.	O
,	O
for	O
media	O
descriptor	O
.	O
</s>
<s>
This	O
results	O
in	O
data	O
cluster	O
numbers	O
2	O
...	O
4085	O
(	O
)	O
for	O
FAT12	B-Application
,	O
2	O
...	O
65525	O
(	O
)	O
for	O
FAT16	B-Application
,	O
and	O
2	O
...	O
268435445	O
(	O
)	O
for	O
FAT32	B-Application
.	O
</s>
<s>
The	O
only	O
available	O
values	O
reserved	O
for	O
future	O
standardization	O
are	O
therefore	O
(	O
FAT12	B-Application
)	O
and	O
(	O
FAT16	B-Application
)	O
.	O
</s>
<s>
As	O
noted	O
below	O
"	O
less	O
than	O
4085	O
"	O
is	O
also	O
used	O
for	O
Linux	O
implementations	O
,	O
or	O
as	O
Microsoft	O
's	O
FAT	B-Application
specification	I-Application
puts	O
it	O
:	O
</s>
<s>
when	O
...	O
it	O
says	O
<	O
,	O
it	O
does	O
not	O
mean	O
<=	O
.	O
</s>
<s>
The	O
first	O
number	O
for	O
FAT12	B-Application
is	O
4085	O
;	O
the	O
second	O
number	O
for	O
FAT16	B-Application
is	O
65525	O
.	O
</s>
<s>
The	O
FAT	O
file	B-Application
system	I-Application
does	O
not	O
contain	O
built-in	O
mechanisms	O
which	O
prevent	O
newly	O
written	O
files	O
from	O
becoming	O
scattered	O
across	O
the	O
partition	O
.	O
</s>
<s>
While	O
the	O
design	B-Application
of	I-Application
the	I-Application
FAT	I-Application
file	I-Application
system	I-Application
does	O
not	O
cause	O
any	O
organizational	O
overhead	O
in	O
disk	O
structures	O
or	O
reduce	O
the	O
amount	O
of	O
free	O
storage	O
space	O
with	O
increased	O
amounts	O
of	O
fragmentation	B-Architecture
,	O
as	O
it	O
occurs	O
with	O
external	O
fragmentation	B-Architecture
,	O
the	O
time	O
required	O
to	O
read	O
and	O
write	O
fragmented	O
files	O
will	O
increase	O
as	O
the	O
operating	O
system	O
will	O
have	O
to	O
follow	O
the	O
cluster	O
chains	O
in	O
the	O
FAT	O
(	O
with	O
parts	O
having	O
to	O
be	O
loaded	O
into	O
memory	O
first	O
in	O
particular	O
on	O
large	O
volumes	O
)	O
and	O
read	O
the	O
corresponding	O
data	O
physically	O
scattered	O
over	O
the	O
whole	O
medium	O
reducing	O
chances	O
for	O
the	O
low-level	O
block	O
device	B-Application
driver	I-Application
to	O
perform	O
multi-sector	O
disk	O
I/O	O
or	O
initiate	O
larger	O
DMA	O
transfers	O
,	O
thereby	O
effectively	O
increasing	O
I/O	O
protocol	O
overhead	O
as	O
well	O
as	O
arm	O
movement	O
and	O
head	O
settle	O
times	O
inside	O
the	O
disk	O
drive	O
.	O
</s>
<s>
Also	O
,	O
file	O
operations	O
will	O
become	O
slower	O
with	O
growing	O
fragmentation	B-Architecture
as	O
it	O
takes	O
increasingly	O
longer	O
for	O
the	O
operating	O
system	O
to	O
find	O
files	O
or	O
free	O
clusters	O
.	O
</s>
<s>
Other	O
file	B-Application
systems	I-Application
,	O
e.g.	O
,	O
HPFS	B-Application
or	O
exFAT	B-Application
,	O
use	O
free	B-Application
space	I-Application
bitmaps	I-Application
that	O
indicate	O
used	O
and	O
available	O
clusters	O
,	O
which	O
could	O
then	O
be	O
quickly	O
looked	O
up	O
in	O
order	O
to	O
find	O
free	O
contiguous	O
areas	O
.	O
</s>
<s>
Another	O
solution	O
is	O
the	O
linkage	O
of	O
all	O
free	O
clusters	O
into	O
one	O
or	O
more	O
lists	O
(	O
as	O
is	O
done	O
in	O
Unix	B-Application
file	B-Application
systems	I-Application
)	O
.	O
</s>
<s>
In	O
fact	O
,	O
seeking	O
for	O
files	O
in	O
large	O
subdirectories	B-Application
or	O
computing	O
the	O
free	O
disk	O
space	O
on	O
FAT	O
volumes	O
is	O
one	O
of	O
the	O
most	O
resource	O
intensive	O
operations	O
,	O
as	O
it	O
requires	O
reading	O
the	O
directory	B-Application
tables	I-Application
or	O
even	O
the	O
entire	O
FAT	O
linearly	O
.	O
</s>
<s>
Since	O
the	O
total	O
amount	O
of	O
clusters	O
and	O
the	O
size	O
of	O
their	O
entries	O
in	O
the	O
FAT	O
was	O
still	O
small	O
on	O
FAT12	B-Application
and	O
FAT16	B-Application
volumes	O
,	O
this	O
could	O
still	O
be	O
tolerated	O
on	O
FAT12	B-Application
and	O
FAT16	B-Application
volumes	O
most	O
of	O
the	O
time	O
,	O
considering	O
that	O
the	O
introduction	O
of	O
more	O
sophisticated	O
disk	O
structures	O
would	O
have	O
also	O
increased	O
the	O
complexity	O
and	O
memory	O
footprint	O
of	O
real-mode	O
operating	O
systems	O
with	O
their	O
minimum	O
total	O
memory	O
requirements	O
of	O
128	O
KB	O
or	O
less	O
(	O
such	O
as	O
with	O
DOS	O
)	O
for	O
which	O
FAT	O
has	O
been	O
designed	O
and	O
optimized	O
originally	O
.	O
</s>
<s>
With	O
the	O
introduction	O
of	O
FAT32	B-Application
,	O
long	O
seek	O
and	O
scan	O
times	O
became	O
more	O
apparent	O
,	O
particularly	O
on	O
very	O
large	O
volumes	O
.	O
</s>
<s>
A	O
possible	O
justification	O
suggested	O
by	O
Microsoft	O
's	O
Raymond	O
Chen	O
for	O
limiting	O
the	O
maximum	O
size	O
of	O
FAT32	B-Application
partitions	O
created	O
on	O
Windows	O
was	O
the	O
time	O
required	O
to	O
perform	O
a	O
"	O
DIR	B-Device
"	O
operation	O
,	O
which	O
always	O
displays	O
the	O
free	O
disk	O
space	O
as	O
the	O
last	O
line	O
.	O
</s>
<s>
FAT32	B-Application
therefore	O
introduced	O
a	O
special	B-Application
file	I-Application
system	O
information	O
sector	O
where	O
the	O
previously	O
computed	O
amount	O
of	O
free	O
space	O
is	O
preserved	O
over	O
power	O
cycles	O
,	O
so	O
that	O
the	O
free	O
space	O
counter	O
needs	O
to	O
be	O
recalculated	O
only	O
when	O
a	O
removable	O
FAT32	B-Application
formatted	O
medium	O
gets	O
ejected	O
without	O
first	O
unmounting	O
it	O
or	O
if	O
the	O
system	O
is	O
switched	O
off	O
without	O
properly	O
shutting	O
down	O
the	O
operating	O
system	O
,	O
a	O
problem	O
mostly	O
visible	O
with	O
pre-ATX-style	O
PCs	O
,	O
on	O
plain	O
DOS	O
systems	O
and	O
some	O
battery-powered	O
consumer	O
products	O
.	O
</s>
<s>
With	O
the	O
huge	O
cluster	O
sizes	O
(	O
16	O
KB	O
,	O
32	O
KB	O
,	O
64	O
KB	O
)	O
forced	O
by	O
larger	O
FAT	O
partitions	O
,	O
internal	O
fragmentation	B-Architecture
in	O
form	O
of	O
disk	O
space	O
waste	O
by	O
file	O
slack	O
due	O
to	O
cluster	O
overhang	O
(	O
as	O
files	O
are	O
rarely	O
exact	O
multiples	O
of	O
cluster	O
size	O
)	O
starts	O
to	O
be	O
a	O
problem	O
as	O
well	O
,	O
especially	O
when	O
there	O
are	O
a	O
great	O
many	O
small	O
files	O
.	O
</s>
<s>
Various	O
optimizations	O
and	O
tweaks	O
to	O
the	O
implementation	O
of	O
FAT	O
file	B-Application
system	I-Application
drivers	O
,	O
block	O
device	B-Application
drivers	I-Application
and	O
disk	O
tools	O
have	O
been	O
devised	O
to	O
overcome	O
most	O
of	O
the	O
performance	O
bottlenecks	O
in	O
the	O
file	B-Application
system	I-Application
's	O
inherent	O
design	O
without	O
having	O
to	O
change	O
the	O
layout	O
of	O
the	O
on-disk	O
structures	O
.	O
</s>
<s>
They	O
can	O
be	O
divided	O
into	O
on-line	O
and	O
off-line	O
methods	O
and	O
work	O
by	O
trying	O
to	O
avoid	O
fragmentation	B-Architecture
in	O
the	O
file	B-Application
system	I-Application
in	O
the	O
first	O
place	O
,	O
deploying	O
methods	O
to	O
better	O
cope	O
with	O
existing	O
fragmentation	B-Architecture
,	O
and	O
by	O
reordering	O
and	O
optimizing	O
the	O
on-disk	O
structures	O
.	O
</s>
<s>
With	O
optimizations	O
in	O
place	O
,	O
the	O
performance	O
on	O
FAT	O
volumes	O
can	O
often	O
reach	O
that	O
of	O
more	O
sophisticated	O
file	B-Application
systems	I-Application
in	O
practical	O
scenarios	O
,	O
while	O
at	O
the	O
same	O
time	O
retaining	O
the	O
advantage	O
of	O
being	O
accessible	O
even	O
on	O
very	O
small	O
or	O
old	O
systems	O
.	O
</s>
<s>
This	O
not	O
only	O
helps	O
to	O
maintain	O
the	O
integrity	O
of	O
deleted	O
files	O
for	O
as	O
long	O
as	O
possible	O
but	O
also	O
speeds	O
up	O
file	O
allocations	O
and	O
avoids	O
fragmentation	B-Architecture
,	O
since	O
never	O
before	O
allocated	O
disk	O
space	O
is	O
always	O
unfragmented	O
.	O
</s>
<s>
These	O
pointers	O
are	O
initialized	O
to	O
point	O
to	O
the	O
start	O
of	O
the	O
FATs	O
after	O
bootup	O
,	O
but	O
on	O
FAT32	B-Application
volumes	O
,	O
DOS	O
7.1	O
and	O
higher	O
will	O
attempt	O
to	O
retrieve	O
the	O
last	O
position	O
from	O
the	O
FS	O
Information	O
Sector	O
.	O
</s>
<s>
This	O
mechanism	O
is	O
defeated	O
,	O
however	O
,	O
if	O
an	O
application	O
often	O
deletes	O
and	O
recreates	O
temporary	O
files	O
as	O
the	O
operating	O
system	O
would	O
then	O
try	O
to	O
maintain	O
the	O
integrity	O
of	O
void	O
data	O
effectively	O
causing	O
more	O
fragmentation	B-Architecture
in	O
the	O
end	O
.	O
</s>
<s>
Additionally	O
,	O
directory	B-Application
entries	O
of	O
deleted	O
files	O
will	O
be	O
marked	O
since	O
DOS	O
3.0	O
.	O
</s>
<s>
DOS	O
5.0	O
and	O
higher	O
will	O
start	O
to	O
reuse	O
these	O
entries	O
only	O
when	O
previously	O
unused	O
directory	B-Application
entries	O
have	O
been	O
used	O
up	O
in	O
the	O
table	O
and	O
the	O
system	O
would	O
otherwise	O
have	O
to	O
expand	O
the	O
table	O
itself	O
.	O
</s>
<s>
Since	O
DOS	O
3.3	O
the	O
operating	O
system	O
provides	O
means	O
to	O
improve	O
the	O
performance	O
of	O
file	O
operations	O
with	O
FASTOPEN	B-Application
by	O
keeping	O
track	O
of	O
the	O
position	O
of	O
recently	O
opened	O
files	O
or	O
directories	B-Application
in	O
various	O
forms	O
of	O
lists	O
(	O
MS-DOS/PCDOS	O
)	O
or	O
hash	O
tables	O
(	O
DR-DOS	B-Application
)	O
,	O
which	O
can	O
reduce	O
file	O
seek	O
and	O
open	O
times	O
significantly	O
.	O
</s>
<s>
Before	O
DOS	O
5.0	O
special	O
care	O
must	O
be	O
taken	O
when	O
using	O
such	O
mechanisms	O
in	O
conjunction	O
with	O
disk	O
defragmentation	O
software	O
bypassing	O
the	O
file	B-Application
system	I-Application
or	O
disk	O
drivers	O
.	O
</s>
<s>
Windows	B-Device
NT	I-Device
will	O
allocate	O
disk	O
space	O
to	O
files	O
on	O
FAT	O
in	O
advance	O
,	O
selecting	O
large	O
contiguous	O
areas	O
,	O
but	O
in	O
case	O
of	O
a	O
failure	O
,	O
files	O
which	O
were	O
being	O
appended	O
will	O
appear	O
larger	O
than	O
they	O
were	O
ever	O
written	O
into	O
,	O
with	O
a	O
lot	O
of	O
random	O
data	O
at	O
the	O
end	O
.	O
</s>
<s>
Also	O
,	O
operating	O
on	O
the	O
logically	O
high	O
level	O
of	O
files	O
and	O
cluster-chains	O
instead	O
of	O
on	O
sector	O
or	O
track	O
level	O
,	O
it	O
becomes	O
possible	O
to	O
avoid	O
some	O
degree	O
of	O
file	O
fragmentation	B-Architecture
in	O
the	O
first	O
place	O
or	O
to	O
carry	O
out	O
local	O
file	O
defragmentation	O
and	O
reordering	O
of	O
directory	B-Application
entries	O
based	O
on	O
their	O
names	O
or	O
access	O
patterns	O
in	O
the	O
background	O
.	O
</s>
<s>
Some	O
of	O
the	O
perceived	O
problems	O
with	O
fragmentation	B-Architecture
of	O
FAT	O
file	B-Application
systems	I-Application
also	O
result	O
from	O
performance	O
limitations	O
of	O
the	O
underlying	O
block	O
device	B-Application
drivers	I-Application
,	O
which	O
becomes	O
more	O
visible	O
the	O
lesser	O
memory	O
is	O
available	O
for	O
sector	O
buffering	O
and	O
track	O
blocking/deblocking	O
:	O
</s>
<s>
While	O
the	O
single-tasking	O
DOS	O
had	O
provisions	O
for	O
multi-sector	O
reads	O
and	O
track	O
blocking/deblocking	O
,	O
the	O
operating	O
system	O
and	O
the	O
traditional	O
PC	O
hard	O
disk	O
architecture	O
(	O
only	O
one	O
outstanding	O
input/output	O
request	O
at	O
a	O
time	O
and	O
no	B-General_Concept
DMA	I-General_Concept
transfers	I-General_Concept
)	O
originally	O
did	O
not	O
contain	O
mechanisms	O
which	O
could	O
alleviate	O
fragmentation	B-Architecture
by	O
asynchronously	O
prefetching	O
next	O
data	O
while	O
the	O
application	O
was	O
processing	O
the	O
previous	O
chunks	O
.	O
</s>
<s>
Later	O
DOS	O
versions	O
also	O
provided	O
built-in	O
support	O
for	O
look-ahead	O
sector	O
buffering	O
and	O
came	O
with	O
dynamically	O
loadable	O
disk	O
caching	O
programs	O
working	O
on	O
physical	O
or	O
logical	O
sector	O
level	O
,	O
often	O
utilizing	O
EMS	B-Device
or	O
XMS	B-Device
memory	I-Device
and	O
sometimes	O
providing	O
adaptive	O
caching	O
strategies	O
or	O
even	O
run	O
in	O
protected	B-Application
mode	I-Application
through	O
DPMS	O
or	O
Cloaking	O
to	O
increase	O
performance	O
by	O
gaining	O
direct	O
access	O
to	O
the	O
cached	O
data	O
in	O
linear	O
memory	O
rather	O
than	O
through	O
conventional	O
DOS	O
APIs	O
.	O
</s>
<s>
VFAT	B-Application
Long	O
File	O
Names	O
(	O
LFNs	O
)	O
are	O
stored	O
on	O
a	O
FAT	O
file	B-Application
system	I-Application
using	O
a	O
trick	O
:	O
adding	O
additional	O
entries	O
into	O
the	O
directory	B-Application
before	O
the	O
normal	O
file	O
entry	O
.	O
</s>
<s>
The	O
additional	O
entries	O
are	O
marked	O
with	O
the	O
Volume	O
Label	O
,	O
System	O
,	O
Hidden	O
,	O
and	O
Read	O
Only	O
attributes	O
(	O
yielding	O
)	O
,	O
which	O
is	O
a	O
combination	O
that	O
is	O
not	O
expected	O
in	O
the	O
MS-DOS	B-Application
environment	O
,	O
and	O
therefore	O
ignored	O
by	O
MS-DOS	B-Application
programs	O
and	O
third-party	O
utilities	O
.	O
</s>
<s>
Notably	O
,	O
a	O
directory	B-Application
containing	O
only	O
volume	O
labels	O
is	O
considered	O
as	O
empty	O
and	O
is	O
allowed	O
to	O
be	O
deleted	O
;	O
such	O
a	O
situation	O
appears	O
if	O
files	O
created	O
with	O
long	O
names	O
are	O
deleted	O
from	O
plain	O
DOS	O
.	O
</s>
<s>
Because	O
older	O
versions	O
of	O
DOS	O
could	O
mistake	O
LFN	O
names	O
in	O
the	O
root	O
directory	B-Application
for	O
the	O
volume	O
label	O
,	O
VFAT	B-Application
was	O
designed	O
to	O
create	O
a	O
blank	O
volume	O
label	O
in	O
the	O
root	O
directory	B-Application
before	O
adding	O
any	O
LFN	O
name	O
entries	O
(	O
if	O
a	O
volume	O
label	O
did	O
not	O
already	O
exist	O
)	O
.	O
</s>
<s>
LFN	O
entries	O
use	O
the	O
following	O
format	B-Application
:	O
</s>
<s>
On	O
FAT12	B-Application
and	O
FAT16	B-Application
volumes	O
,	O
testing	O
for	O
the	O
values	O
at	O
to	O
be	O
zero	O
and	O
at	O
to	O
be	O
non-zero	O
can	O
be	O
used	O
to	O
distinguish	O
between	O
VFAT	B-Application
LFNs	O
and	O
pending	O
delete	O
files	O
under	O
DELWATCH	O
.	O
</s>
<s>
A	O
checksum	B-Algorithm
also	O
allows	O
verification	O
of	O
whether	O
a	O
long	O
file	O
name	O
matches	O
the	O
8.3	O
name	O
;	O
such	O
a	O
mismatch	O
could	O
occur	O
if	O
a	O
file	O
was	O
deleted	O
and	O
re-created	O
using	O
DOS	O
in	O
the	O
same	O
directory	B-Application
position	O
.	O
</s>
<s>
The	O
checksum	B-Algorithm
is	O
calculated	O
using	O
the	O
algorithm	O
below	O
.	O
</s>
<s>
(	O
pFCBName	O
is	O
a	O
pointer	O
to	O
the	O
name	O
as	O
it	O
appears	O
in	O
a	O
regular	O
directory	B-Application
entry	O
,	O
i.e.	O
</s>
<s>
Any	O
unused	O
space	O
in	O
the	O
filename	O
is	O
padded	O
with	O
space	O
characters	O
(	O
ASCII	B-Protocol
)	O
.	O
</s>
<s>
If	O
a	O
filename	O
contains	O
only	O
lowercase	O
letters	O
,	O
or	O
is	O
a	O
combination	O
of	O
a	O
lowercase	O
basename	O
with	O
an	O
uppercase	O
extension	O
,	O
or	O
vice	O
versa	O
;	O
and	O
has	O
no	O
special	O
characters	O
,	O
and	O
fits	O
within	O
the	O
8.3	O
limits	O
,	O
a	O
VFAT	B-Application
entry	O
is	O
not	O
created	O
on	O
Windows	B-Device
NT	I-Device
and	O
later	O
versions	O
of	O
Windows	O
such	O
as	O
XP	B-Application
.	O
</s>
<s>
Instead	O
,	O
two	O
bits	O
in	O
byte	O
of	O
the	O
directory	B-Application
entry	O
are	O
used	O
to	O
indicate	O
that	O
the	O
filename	O
should	O
be	O
considered	O
as	O
entirely	O
or	O
partially	O
lowercase	O
.	O
</s>
<s>
This	O
creates	O
a	O
backwards-compatibility	O
problem	O
with	O
older	O
Windows	O
versions	O
(	O
Windows	B-Application
95	I-Application
/	O
98	O
/	O
98	O
SE	O
/	O
ME	O
)	O
that	O
see	O
all-uppercase	O
filenames	O
if	O
this	O
extension	O
has	O
been	O
used	O
,	O
and	O
therefore	O
can	O
change	O
the	O
name	O
of	O
a	O
file	O
when	O
it	O
is	O
transported	O
between	O
operating	O
systems	O
,	O
such	O
as	O
on	O
a	O
USB	O
flash	O
drive	O
.	O
</s>
<s>
Current	O
2.6.x	O
versions	O
of	O
Linux	O
will	O
recognize	O
this	O
extension	O
when	O
reading	O
(	O
source	O
:	O
kernel	O
2.6.18	O
/fs/fat/dir.c	O
and	O
fs/vfat/namei.c	O
)	O
;	O
the	O
mount	O
option	O
shortname	O
determines	O
whether	O
this	O
feature	O
is	O
used	O
when	O
writing	O
.	O
</s>
