<s>
In	O
computer	B-Device
disk	I-Device
storage	O
,	O
a	O
sector	O
is	O
a	O
subdivision	O
of	O
a	O
track	B-Device
on	O
a	O
magnetic	B-Architecture
disk	I-Architecture
or	O
optical	B-Device
disc	I-Device
.	O
</s>
<s>
Each	O
sector	O
stores	O
a	O
fixed	O
amount	O
of	O
user-accessible	O
data	O
,	O
traditionally	O
512	B-Application
bytes	I-Application
for	O
hard	B-Device
disk	I-Device
drives	I-Device
(	O
HDDs	O
)	O
and	O
2048	O
bytes	B-Application
for	O
CD-ROMs	B-Device
and	O
DVD-ROMs	O
.	O
</s>
<s>
Newer	O
HDDs	O
use	O
4096-byte	O
(	O
4KiB	O
)	O
sectors	O
,	O
which	O
are	O
known	O
as	O
the	O
Advanced	B-Device
Format	I-Device
(	O
AF	O
)	O
.	O
</s>
<s>
The	O
sector	O
is	O
the	O
minimum	O
storage	O
unit	O
of	O
a	O
hard	B-Device
drive	I-Device
.	O
</s>
<s>
Most	O
disk	B-Application
partitioning	I-Application
schemes	O
are	O
designed	O
to	O
have	O
files	O
occupy	O
an	O
integral	O
number	O
of	O
sectors	O
regardless	O
of	O
the	O
file	O
's	O
actual	O
size	O
.	O
</s>
<s>
In	O
practice	O
,	O
operating	O
systems	O
typically	O
operate	O
on	O
blocks	B-General_Concept
of	I-General_Concept
data	I-General_Concept
,	O
which	O
may	O
span	O
multiple	O
sectors	O
.	O
</s>
<s>
Geometrically	O
,	O
the	O
word	O
sector	O
means	O
a	O
portion	O
of	O
a	O
disk	B-Device
between	O
a	O
center	O
,	O
two	O
radii	B-Protocol
and	O
a	O
corresponding	O
arc	O
(	O
see	O
Figure	O
1	O
,	O
item	O
B	O
)	O
,	O
which	O
is	O
shaped	O
like	O
a	O
slice	B-Application
of	O
a	O
pie	O
.	O
</s>
<s>
Thus	O
,	O
the	O
disk	B-Application
sector	I-Application
(	O
Figure	O
1	O
,	O
item	O
C	O
)	O
refers	O
to	O
the	O
intersection	O
of	O
a	O
track	B-Device
and	O
geometrical	O
sector	O
.	O
</s>
<s>
In	O
modern	O
disk	B-Device
drives	I-Device
,	O
each	O
physical	O
sector	O
is	O
made	O
up	O
of	O
two	O
basic	O
parts	O
,	O
the	O
sector	O
header	B-General_Concept
area	O
(	O
typically	O
called	O
"	O
ID	O
"	O
)	O
and	O
the	O
data	O
area	O
.	O
</s>
<s>
The	O
sector	O
header	B-General_Concept
contains	O
information	O
used	O
by	O
the	O
drive	O
and	O
controller	O
;	O
this	O
information	O
includes	O
sync	O
bytes	B-Application
,	O
address	B-Application
identification	I-Application
,	O
flaw	O
flag	O
and	O
error	O
detection	O
and	O
correction	O
information	O
.	O
</s>
<s>
The	O
header	B-General_Concept
may	O
also	O
include	O
an	O
alternate	O
address	O
to	O
be	O
used	O
if	O
the	O
data	O
area	O
is	O
undependable	O
.	O
</s>
<s>
The	O
address	B-Application
identification	I-Application
is	O
used	O
to	O
ensure	O
that	O
the	O
mechanics	O
of	O
the	O
drive	O
have	O
positioned	O
the	O
read/write	O
head	O
over	O
the	O
correct	O
location	O
.	O
</s>
<s>
The	O
data	O
area	O
contains	O
the	O
sync	O
bytes	B-Application
,	O
user	O
data	O
and	O
an	O
error-correcting	B-Error_Name
code	I-Error_Name
(	O
ECC	O
)	O
that	O
is	O
used	O
to	O
check	O
and	O
possibly	O
correct	O
errors	O
that	O
may	O
have	O
been	O
introduced	O
into	O
the	O
data	O
.	O
</s>
<s>
The	O
first	O
disk	B-Device
drive	I-Device
,	O
the	O
1957	O
IBM	O
350	O
disk	B-Device
storage	I-Device
,	O
had	O
ten	O
100	O
character	O
sectors	O
per	O
track	B-Device
;	O
each	O
character	O
was	O
six	O
bits	O
and	O
included	O
a	O
parity	O
bit	O
.	O
</s>
<s>
The	O
number	O
of	O
sectors	O
per	O
track	B-Device
was	O
identical	O
on	O
all	O
recording	O
surfaces	O
.	O
</s>
<s>
The	O
1961	O
IBM	O
1301	O
disk	B-Device
storage	I-Device
introduced	O
variable	O
length	O
sectors	O
,	O
termed	O
records	O
by	O
IBM	O
,	O
and	O
added	O
to	O
each	O
record	O
a	O
record	O
address	O
field	O
separate	O
from	O
the	O
data	O
in	O
a	O
record	O
(	O
sector	O
)	O
.	O
</s>
<s>
All	O
modern	O
disk	B-Device
drives	I-Device
have	O
sector	O
address	O
fields	O
,	O
called	O
ID	O
fields	O
,	O
separate	O
from	O
the	O
data	O
in	O
a	O
sector	O
.	O
</s>
<s>
Also	O
in	O
1961	O
Bryant	O
with	O
its	O
4000	O
series	O
introduced	O
the	O
concept	O
of	O
zoned	O
recording	O
which	O
allowed	O
the	O
number	O
of	O
sectors	O
per	O
track	B-Device
to	O
vary	O
as	O
a	O
function	O
of	O
the	O
track	B-Device
's	O
diameter	O
-	O
there	O
are	O
more	O
sectors	O
on	O
an	O
outer	O
track	B-Device
than	O
on	O
an	O
inner	O
track	B-Device
.	O
</s>
<s>
The	O
disk	B-Device
drives	I-Device
announced	O
with	O
the	O
IBM	B-Application
System/360	I-Application
in	O
1964	O
detected	O
errors	O
in	O
all	O
fields	O
of	O
their	O
sectors	O
(	O
records	O
)	O
with	O
a	O
cyclic	O
redundancy	O
check	O
(	O
CRC	O
)	O
replacing	O
parity	O
per	O
character	O
detection	O
of	O
prior	O
generations	O
.	O
</s>
<s>
These	O
IBM	O
physical	O
sectors	O
,	O
called	O
records	O
,	O
have	O
three	O
basic	O
parts	O
,	O
a	O
Count	O
field	O
which	O
acts	O
as	O
an	O
ID	O
field	O
,	O
a	O
Key	O
field	O
not	O
present	O
in	O
most	O
disk	B-Device
drive	I-Device
sectors	O
and	O
a	O
Data	O
field	O
,	O
frequently	O
called	O
the	O
CKD	B-Application
format	O
for	O
a	O
record	O
.	O
</s>
<s>
The	O
1970	O
IBM	O
3330	O
disk	B-Device
storage	I-Device
replaced	O
the	O
CRC	O
on	O
the	O
data	O
field	O
of	O
each	O
sector	O
with	O
an	O
error	B-Error_Name
correcting	I-Error_Name
code	I-Error_Name
(	O
ECC	O
)	O
to	O
improve	O
data	O
integrity	O
by	O
detecting	O
most	O
errors	O
and	O
allowing	O
correction	O
of	O
many	O
errors	O
.	O
</s>
<s>
Ultimately	O
all	O
fields	O
of	O
disk	B-Application
sectors	I-Application
had	O
ECCs	O
.	O
</s>
<s>
Prior	O
to	O
the	O
1980s	O
there	O
was	O
little	O
standardization	O
of	O
sector	O
sizes	O
;	O
disk	B-Device
drives	I-Device
had	O
a	O
maximum	O
number	O
of	O
bits	O
per	O
track	B-Device
and	O
various	O
system	O
manufacturers	O
subdivided	O
the	O
track	B-Device
into	O
different	O
sector	O
sizes	O
to	O
suit	O
their	O
OSes	O
and	O
applications	O
.	O
</s>
<s>
The	O
popularity	O
of	O
the	O
PC	B-Device
beginning	O
in	O
the	O
1980s	O
and	O
the	O
advent	O
of	O
the	O
IDE	O
interface	O
in	O
the	O
late	O
1980s	O
led	O
to	O
a	O
512-byte	O
sector	O
becoming	O
an	O
industry	O
standard	O
sector	O
size	O
for	O
HDDs	O
and	O
similar	O
storage	O
devices	O
.	O
</s>
<s>
In	O
the	O
1970s	O
IBM	O
added	O
fixed-block	B-Device
architecture	I-Device
Direct	B-Application
Access	I-Application
Storage	I-Application
Devices	I-Application
(	O
FBA	O
DASDs	B-Application
)	O
to	O
its	O
line	O
of	O
CKD	B-Application
DASD	B-Application
.	O
</s>
<s>
CKD	B-Application
DASD	B-Application
supported	O
multiple	O
variable	O
length	O
sectors	O
while	O
the	O
IBM	O
FBA	O
DASD	B-Application
supported	O
sector	O
sizes	O
of	O
512	O
,	O
1024	O
,	O
2048	O
,	O
or	O
4096	O
bytes	B-Application
.	O
</s>
<s>
In	O
2000	O
the	O
industry	O
trade	O
organization	O
,	O
International	O
Disk	B-Device
Drive	I-Device
Equipment	O
and	O
Materials	O
Association	O
(	O
IDEMA	B-Device
)	O
started	O
work	O
to	O
define	O
the	O
implementation	O
and	O
standards	O
that	O
would	O
govern	O
sector	O
size	O
formats	O
exceeding	O
512	B-Application
bytes	I-Application
to	O
accommodate	O
future	O
increases	O
in	O
data	O
storage	O
capacities	O
.	O
</s>
<s>
By	O
the	O
end	O
of	O
2007	O
in	O
anticipation	O
of	O
a	O
future	O
IDEMA	B-Device
standard	O
,	O
Samsung	O
and	O
Toshiba	O
began	O
shipments	O
of	O
1.8-inch	O
hard	B-Device
disk	I-Device
drives	I-Device
with	O
4096	O
byte	B-Application
sectors	O
.	O
</s>
<s>
In	O
2010	O
IDEMA	B-Device
completed	O
the	O
Advanced	B-Device
Format	I-Device
standard	O
for	O
4096	O
sector	O
drives	O
,	O
setting	O
the	O
date	O
for	O
the	O
transition	O
from	O
512	O
to	O
4096	O
byte	B-Application
sectors	O
as	O
January	O
2011	O
for	O
all	O
manufacturers	O
,	O
and	O
Advanced	B-Device
Format	I-Device
drives	I-Device
soon	O
became	O
prevalent	O
.	O
</s>
<s>
While	O
sector	O
specifically	O
means	O
the	O
physical	O
disk	B-Device
area	O
,	O
the	O
term	O
block	O
has	O
been	O
used	O
loosely	O
to	O
refer	O
to	O
a	O
small	O
chunk	O
of	O
data	O
.	O
</s>
<s>
In	O
the	O
context	O
of	O
data	O
storage	O
,	O
a	O
filesystem	B-General_Concept
block	I-General_Concept
is	O
an	O
abstraction	O
over	O
disk	B-Application
sectors	I-Application
possibly	O
encompassing	O
multiple	O
sectors	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
Unix	B-Application
program	B-Application
dd	B-Application
allows	O
one	O
to	O
set	O
the	O
block	B-General_Concept
size	I-General_Concept
to	O
be	O
used	O
during	O
execution	O
with	O
the	O
parameter	O
bs	O
=	O
bytes	B-Application
.	O
</s>
<s>
This	O
specifies	O
the	O
size	O
of	O
the	O
chunks	O
of	O
data	O
as	O
delivered	O
by	O
dd	B-Application
,	O
and	O
is	O
unrelated	O
to	O
sectors	O
or	O
filesystem	B-Application
blocks	O
.	O
</s>
<s>
In	O
Linux	O
,	O
disk	B-Application
sector	I-Application
size	O
can	O
be	O
determined	O
with	O
sudo	O
fdisk	O
-l	O
|	O
grep	O
"	O
Sector	O
size	O
"	O
and	O
block	B-General_Concept
size	I-General_Concept
can	O
be	O
determined	O
with	O
sudo	O
blockdev	O
--getbsz	O
/dev/sda	O
.	O
</s>
<s>
In	O
computer	B-Application
file	I-Application
systems	I-Application
,	O
a	O
cluster	O
(	O
sometimes	O
also	O
called	O
allocation	O
unit	O
or	O
block	O
)	O
is	O
a	O
unit	O
of	O
disk	B-Device
space	O
allocation	O
for	O
files	O
and	O
directories	O
.	O
</s>
<s>
To	O
reduce	O
the	O
overhead	O
of	O
managing	O
on-disk	O
data	O
structures	O
,	O
the	O
filesystem	B-Application
does	O
not	O
allocate	O
individual	O
disk	B-Application
sectors	I-Application
by	O
default	O
,	O
but	O
contiguous	O
groups	O
of	O
sectors	O
,	O
called	O
clusters	O
.	O
</s>
<s>
On	O
a	O
disk	B-Device
that	O
uses	O
512-byte	O
sectors	O
,	O
a	O
512-byte	O
cluster	O
contains	O
one	O
sector	O
,	O
whereas	O
a	O
4-kibibyte	O
(	O
KiB	O
)	O
cluster	O
contains	O
eight	O
sectors	O
.	O
</s>
<s>
A	O
cluster	O
is	O
the	O
smallest	O
logical	O
amount	O
of	O
disk	B-Device
space	O
that	O
can	O
be	O
allocated	O
to	O
hold	O
a	O
file	O
.	O
</s>
<s>
Storing	O
small	O
files	O
on	O
a	O
filesystem	B-Application
with	O
large	O
clusters	O
will	O
therefore	O
waste	O
disk	B-Device
space	O
;	O
such	O
wasted	O
disk	B-Device
space	O
is	O
called	O
slack	O
space	O
.	O
</s>
<s>
However	O
,	O
a	O
larger	O
cluster	O
size	O
reduces	O
bookkeeping	O
overhead	O
and	O
fragmentation	B-Application
,	O
which	O
may	O
improve	O
reading	B-General_Concept
and	O
writing	O
speed	O
overall	O
.	O
</s>
<s>
A	O
cluster	O
need	O
not	O
be	O
physically	O
contiguous	O
on	O
the	O
disk	B-Device
;	O
it	O
may	O
span	O
more	O
than	O
one	O
track	B-Device
or	O
,	O
if	O
sector	B-Application
interleaving	I-Application
is	O
used	O
,	O
may	O
even	O
be	O
discontiguous	O
within	O
a	O
track	B-Device
.	O
</s>
<s>
This	O
should	O
not	O
be	O
confused	O
with	O
fragmentation	B-Application
,	O
as	O
the	O
sectors	O
are	O
still	O
logically	O
contiguous	O
.	O
</s>
<s>
A	O
"	O
lost	O
cluster	O
"	O
occurs	O
when	O
a	O
file	O
is	O
deleted	O
from	O
the	O
directory	O
listing	O
,	O
but	O
the	O
File	B-Application
Allocation	I-Application
Table	I-Application
(	O
FAT	O
)	O
still	O
shows	O
the	O
clusters	O
allocated	O
to	O
the	O
file	O
.	O
</s>
<s>
The	O
term	O
cluster	O
was	O
changed	O
to	O
allocation	O
unit	O
in	O
DOS	B-Device
4.0	O
.	O
</s>
<s>
If	O
a	O
sector	O
is	O
defined	O
as	O
the	O
intersection	O
between	O
a	O
radius	B-Protocol
and	O
a	O
track	B-Device
,	O
as	O
was	O
the	O
case	O
with	O
early	O
hard	B-Device
drives	I-Device
and	O
most	O
floppy	O
disks	B-Device
,	O
the	O
sectors	O
towards	O
the	O
outside	O
of	O
the	O
disk	B-Device
are	O
physically	O
longer	O
than	O
those	O
nearer	O
the	O
spindle	O
.	O
</s>
<s>
Because	O
each	O
sector	O
still	O
contains	O
the	O
same	O
number	O
of	O
bytes	B-Application
,	O
the	O
outer	O
sectors	O
have	O
lower	O
bit	B-Device
density	I-Device
than	O
the	O
inner	O
ones	O
,	O
which	O
is	O
an	O
inefficient	O
use	O
of	O
the	O
magnetic	O
surface	O
.	O
</s>
<s>
The	O
solution	O
is	O
zone	B-Architecture
bit	I-Architecture
recording	I-Architecture
,	O
wherein	O
the	O
disk	B-Device
is	O
divided	O
into	O
zones	O
,	O
each	O
encompassing	O
a	O
small	O
number	O
of	O
contiguous	O
tracks	O
.	O
</s>
<s>
This	O
is	O
known	O
as	O
zoned	B-Architecture
bit	I-Architecture
recording	I-Architecture
.	O
</s>
<s>
A	O
consequence	O
of	O
zone	B-Architecture
bit	I-Architecture
recording	I-Architecture
is	O
that	O
contiguous	O
reads	O
and	O
writes	O
are	O
noticeably	O
faster	O
on	O
outer	O
tracks	O
(	O
corresponding	O
to	O
lower	O
block	O
addresses	O
)	O
than	O
on	O
inner	O
tracks	O
,	O
as	O
more	O
bits	O
pass	O
under	O
the	O
head	O
with	O
each	O
rotation	O
;	O
this	O
difference	O
can	O
be	O
25%	O
or	O
more	O
.	O
</s>
<s>
In	O
1998	O
the	O
traditional	O
512-byte	O
sector	O
size	O
was	O
identified	O
as	O
one	O
impediment	O
to	O
increasing	O
capacity	O
which	O
at	O
that	O
time	O
was	O
growing	O
at	O
a	O
rate	O
exceeding	O
Moore	O
's	O
Law	O
.	O
</s>
<s>
Increasing	O
the	O
length	O
of	O
the	O
data	O
field	O
through	O
the	O
implementation	O
of	O
Advanced	B-Device
Format	I-Device
using	O
4096-byte	O
sectors	O
removed	O
this	O
impediment	O
;	O
it	O
increased	O
the	O
efficiency	O
of	O
the	O
data	O
surface	O
area	O
by	O
five	O
to	O
thirteen	O
percent	O
while	O
increasing	O
the	O
strength	O
of	O
the	O
ECC	O
which	O
in	O
turn	O
allowed	O
higher	O
capacity	O
.	O
</s>
<s>
The	O
format	O
was	O
standardized	O
by	O
an	O
industry	O
consortium	O
in	O
2005	O
and	O
by	O
2011	O
incorporated	O
in	O
all	O
new	O
products	O
of	O
all	O
hard	B-Device
drive	I-Device
manufacturers	O
.	O
</s>
