<s>
Cylinder-head-sector	B-Device
(	O
CHS	O
)	O
is	O
an	O
early	O
method	O
for	O
giving	O
addresses	O
to	O
each	O
physical	O
block	O
of	O
data	O
on	O
a	O
hard	B-Device
disk	I-Device
drive	I-Device
.	O
</s>
<s>
It	O
is	O
a	O
3D-coordinate	O
system	O
made	O
out	O
of	O
a	O
vertical	O
coordinate	O
head	B-Device
,	O
a	O
horizontal	O
(	O
or	O
radial	O
)	O
coordinate	O
cylinder	O
,	O
and	O
an	O
angular	O
coordinate	O
sector	O
.	O
</s>
<s>
Head	B-Device
selects	O
a	O
circular	O
surface	O
:	O
a	O
platter	O
in	O
the	O
disk	B-Device
(	O
and	O
one	O
of	O
its	O
two	O
sides	O
)	O
.	O
</s>
<s>
Cylinder	O
is	O
a	O
cylindrical	O
intersection	O
through	O
the	O
stack	O
of	O
platters	B-Device
in	O
a	O
disk	B-Device
,	O
centered	O
around	O
the	O
disk	B-Device
's	O
spindle	O
.	O
</s>
<s>
Combined	O
,	O
cylinder	O
and	O
head	B-Device
intersect	O
to	O
a	O
circular	O
line	O
,	O
or	O
more	O
precisely	O
:	O
a	O
circular	O
strip	O
of	O
physical	O
data	O
blocks	O
called	O
track	B-Device
.	O
</s>
<s>
Sector	O
finally	O
selects	O
which	O
data	O
block	O
in	O
this	O
track	B-Device
is	O
to	O
be	O
addressed	O
,	O
as	O
the	O
track	B-Device
is	O
subdivided	O
into	O
several	O
equally-sized	O
portions	O
,	O
each	O
of	O
which	O
is	O
an	O
arc	O
of	O
(	O
360/n	O
)	O
degrees	O
,	O
where	O
n	O
is	O
the	O
number	O
of	O
sectors	O
in	O
the	O
track	B-Device
.	O
</s>
<s>
CHS	O
addresses	O
were	O
exposed	O
,	O
instead	O
of	O
simple	O
linear	O
addresses	O
(	O
going	O
from	O
0	O
to	O
the	O
total	O
block	O
count	O
on	O
disk	B-Device
-	O
1	O
)	O
,	O
because	O
early	O
hard	B-Device
drives	I-Device
did	O
n't	O
come	O
with	O
an	O
embedded	O
disk	B-General_Concept
controller	I-General_Concept
,	O
that	O
would	O
hide	O
the	O
physical	O
layout	O
.	O
</s>
<s>
A	O
separate	O
generic	O
controller	O
card	O
was	O
used	O
,	O
so	O
that	O
the	O
operating	B-General_Concept
system	I-General_Concept
had	O
to	O
know	O
the	O
exact	O
physical	O
"	O
geometry	O
"	O
of	O
the	O
specific	O
drive	O
attached	O
to	O
the	O
controller	O
,	O
to	O
correctly	O
address	O
data	O
blocks	O
.	O
</s>
<s>
The	O
traditional	O
limits	O
were	O
512	O
bytes/sector	O
×	O
63	O
sectors/track	O
×	O
255	O
heads	O
(	O
tracks/cylinder	O
)	O
×	O
1024	O
cylinders	O
,	O
resulting	O
in	O
a	O
limit	O
of	O
8032.5	O
MiB	O
for	O
the	O
total	O
capacity	O
of	O
a	O
disk	B-Device
.	O
</s>
<s>
As	O
the	O
geometry	O
became	O
more	O
complicated	O
(	O
for	O
example	O
,	O
with	O
the	O
introduction	O
of	O
zone	B-Architecture
bit	I-Architecture
recording	I-Architecture
)	O
and	O
drive	O
sizes	O
grew	O
over	O
time	O
,	O
the	O
CHS	O
addressing	O
method	O
became	O
restrictive	O
.	O
</s>
<s>
Since	O
the	O
late	O
1980s	O
,	O
hard	B-Device
drives	I-Device
began	O
shipping	O
with	O
an	O
embedded	O
disk	B-General_Concept
controller	I-General_Concept
that	O
had	O
good	O
knowledge	O
of	O
the	O
physical	O
geometry	O
;	O
they	O
would	O
however	O
report	O
a	O
false	O
geometry	O
to	O
the	O
computer	O
,	O
e.g.	O
,	O
a	O
larger	O
number	O
of	O
heads	O
than	O
actually	O
present	O
,	O
to	O
gain	O
more	O
addressable	O
space	O
.	O
</s>
<s>
By	O
the	O
mid	O
1990s	O
,	O
hard	B-Device
drive	I-Device
interfaces	O
replaced	O
the	O
CHS	O
scheme	O
with	O
logical	B-Device
block	I-Device
addressing	I-Device
(	O
LBA	O
)	O
,	O
but	O
many	O
tools	O
for	O
manipulating	O
the	O
master	B-Device
boot	I-Device
record	I-Device
(	O
MBR	O
)	O
partition	B-Application
table	O
still	O
aligned	O
partitions	B-Application
to	O
cylinder	O
boundaries	O
;	O
thus	O
,	O
artifacts	O
of	O
CHS	O
addressing	O
were	O
still	O
seen	O
in	O
partitioning	B-Application
software	O
by	O
the	O
late	O
2000s	O
.	O
</s>
<s>
In	O
the	O
early	O
2010s	O
,	O
the	O
disk	B-Device
size	O
limitations	O
imposed	O
by	O
MBR	O
became	O
problematic	O
and	O
the	O
GUID	B-Application
Partition	I-Application
Table	I-Application
(	O
GPT	O
)	O
was	O
designed	O
as	O
a	O
replacement	O
;	O
modern	O
computers	O
using	O
UEFI	B-Architecture
firmware	I-Architecture
without	O
MBR	O
support	O
no	O
longer	O
use	O
any	O
notions	O
from	O
CHS	O
addressing	O
.	O
</s>
<s>
physical	O
block	O
of	O
data	O
)	O
on	O
a	O
disk	B-Device
by	O
their	O
position	O
in	O
a	O
track	B-Device
,	O
where	O
the	O
track	B-Device
is	O
determined	O
by	O
the	O
head	B-Device
and	O
cylinder	O
numbers	O
.	O
</s>
<s>
The	O
terms	O
are	O
explained	O
bottom	O
up	O
,	O
for	O
disk	B-Device
addressing	O
the	O
sector	O
is	O
the	O
smallest	O
unit	O
.	O
</s>
<s>
Disk	B-General_Concept
controllers	I-General_Concept
can	O
introduce	O
address	O
translations	O
to	O
map	O
logical	O
to	O
physical	O
positions	O
,	O
e.g.	O
,	O
zone	B-Architecture
bit	I-Architecture
recording	I-Architecture
stores	O
fewer	O
sectors	O
in	O
shorter	O
(	O
inner	O
)	O
tracks	B-Device
,	O
physical	O
disk	B-Application
formats	I-Application
are	O
not	O
necessarily	O
cylindrical	O
,	O
and	O
sector	O
numbers	O
in	O
a	O
track	B-Device
can	O
be	O
skewed	O
.	O
</s>
<s>
Floppy	B-Device
disks	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	B-Application
(	O
e.g.	O
,	O
PC/AX	O
)	O
,	O
whereby	O
formats	O
with	O
512	O
bytes	B-Application
per	O
physical	O
sector	O
became	O
dominant	O
in	O
the	O
1980s	O
.	O
</s>
<s>
The	O
most	O
common	O
physical	O
sector	O
size	O
for	O
hard	B-Device
disks	I-Device
today	O
is	O
512	O
bytes	B-Application
,	O
but	O
there	O
have	O
been	O
hard	B-Device
disks	I-Device
with	O
520	O
bytes	B-Application
per	O
sector	O
as	O
well	O
for	O
non-IBM	O
compatible	O
machines	O
.	O
</s>
<s>
In	O
2005	O
some	O
Seagate	O
custom	O
hard	B-Device
disks	I-Device
used	O
sector	O
sizes	O
of	O
1024	O
bytes	B-Application
per	O
sector	O
.	O
</s>
<s>
Advanced	B-Device
Format	I-Device
hard	B-Device
disks	I-Device
use	O
4096	O
bytes	B-Application
per	O
physical	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	B-Application
sectors	O
(	O
512e	O
)	O
for	O
a	O
transitional	O
period	O
.	O
</s>
<s>
Magneto-optical	B-Device
drives	I-Device
use	O
sector	O
sizes	O
of	O
512	O
and	O
1024	O
bytes	B-Application
on	O
5.25-inch	O
drives	O
and	O
512	O
and	O
2048	O
bytes	B-Application
on	O
3.5-inch	O
drives	O
.	O
</s>
<s>
In	O
CHS	O
addressing	O
the	O
sector	O
numbers	O
always	O
start	O
at	O
1	O
,	O
there	O
is	O
no	O
sector	O
0	O
,	O
which	O
can	O
lead	O
to	O
confusion	O
since	O
logical	O
sector	O
addressing	O
schemes	O
typically	O
start	O
counting	O
with	O
0	O
,	O
e.g.	O
,	O
logical	B-Device
block	I-Device
addressing	I-Device
(	O
LBA	O
)	O
,	O
or	O
"	O
relative	O
sector	O
addressing	O
"	O
used	O
in	O
DOS	B-Device
.	O
</s>
<s>
For	O
physical	O
disk	B-Device
geometries	O
the	O
maximal	O
sector	O
number	O
is	O
determined	O
by	O
the	O
low	B-Application
level	I-Application
format	I-Application
of	O
the	O
disk	B-Device
.	O
</s>
<s>
However	O
,	O
for	O
disk	B-Device
access	O
with	O
the	O
BIOS	B-Operating_System
of	O
IBM-PC	O
compatible	O
machines	O
,	O
the	O
sector	O
number	O
was	O
encoded	O
in	O
six	O
bits	O
,	O
resulting	O
in	O
a	O
maximal	O
number	O
of	O
111111	O
(	O
63	O
)	O
sectors	O
per	O
track	B-Device
.	O
</s>
<s>
The	O
tracks	B-Device
are	O
the	O
thin	O
concentric	O
circular	O
strips	O
of	O
sectors	O
.	O
</s>
<s>
At	O
least	O
one	O
head	B-Device
is	O
required	O
to	O
read	O
a	O
single	O
track	B-Device
.	O
</s>
<s>
With	O
respect	O
to	O
disk	B-Device
geometries	O
the	O
terms	O
track	B-Device
and	O
cylinder	O
are	O
closely	O
related	O
.	O
</s>
<s>
For	O
a	O
single	O
or	O
double	O
sided	O
floppy	B-Device
disk	I-Device
track	B-Device
is	O
the	O
common	O
term	O
;	O
and	O
for	O
more	O
than	O
two	O
heads	O
cylinder	O
is	O
the	O
common	O
term	O
.	O
</s>
<s>
Strictly	O
speaking	O
a	O
track	B-Device
is	O
a	O
given	O
CH	O
combination	O
consisting	O
ofSPT	O
sectors	O
,	O
while	O
a	O
cylinder	O
consists	O
ofSPT×H	O
sectors	O
.	O
</s>
<s>
A	O
cylinder	O
is	O
a	O
division	O
of	O
data	O
in	O
a	O
disk	B-Device
drive	I-Device
,	O
as	O
used	O
in	O
the	O
CHS	O
addressing	O
mode	O
of	O
a	O
Fixed	B-Device
Block	I-Device
Architecture	I-Device
disk	B-Device
or	O
the	O
cylinder	O
–	O
head	B-Device
–	O
record	O
(	O
CCHHR	O
)	O
addressing	O
mode	O
of	O
a	O
CKD	B-Application
disk	I-Application
.	O
</s>
<s>
The	O
concept	O
is	O
concentric	O
,	O
hollow	O
,	O
cylindrical	O
slices	B-Application
through	O
the	O
physical	O
disks	B-Device
(	O
platters	B-Device
)	O
,	O
collecting	O
the	O
respective	O
circular	O
tracks	B-Device
aligned	O
through	O
the	O
stack	O
of	O
platters	B-Device
.	O
</s>
<s>
The	O
number	O
of	O
cylinders	O
of	O
a	O
disk	B-Device
drive	I-Device
exactly	O
equals	O
the	O
number	O
of	O
tracks	B-Device
on	O
a	O
single	O
surface	O
in	O
the	O
drive	O
.	O
</s>
<s>
It	O
comprises	O
the	O
same	O
track	B-Device
number	O
on	O
each	O
platter	O
,	O
spanning	O
all	O
such	O
tracks	B-Device
across	O
each	O
platter	O
surface	O
that	O
is	O
able	O
to	O
store	O
data	O
(	O
without	O
regard	O
to	O
whether	O
or	O
not	O
the	O
track	B-Device
is	O
"	O
bad	O
"	O
)	O
.	O
</s>
<s>
Cylinders	O
are	O
vertically	O
formed	O
by	O
tracks	B-Device
.	O
</s>
<s>
In	O
other	O
words	O
,	O
track	B-Device
12	O
on	O
platter	O
0	O
plus	O
track	B-Device
12	O
on	O
platter	O
1	O
etc	O
.	O
</s>
<s>
Other	O
forms	O
of	O
Direct	B-Application
Access	I-Application
Storage	I-Application
Device	I-Application
(	O
DASD	B-Application
)	O
,	O
such	O
as	O
drum	B-General_Concept
memory	I-General_Concept
devices	O
or	O
the	O
IBM	B-Device
2321	I-Device
Data	I-Device
Cell	I-Device
,	O
might	O
give	O
blocks	O
addresses	O
that	O
include	O
a	O
cylinder	O
address	O
,	O
although	O
the	O
cylinder	O
address	O
does	O
n't	O
select	O
a	O
(	O
geometric	O
)	O
cylindrical	O
slice	B-Application
of	O
the	O
device	O
.	O
</s>
<s>
A	O
device	O
called	O
a	O
head	B-Device
reads	O
and	O
writes	O
data	O
in	O
a	O
hard	B-Device
drive	I-Device
by	O
manipulating	O
the	O
magnetic	O
medium	O
that	O
composes	O
the	O
surface	O
of	O
an	O
associated	O
disk	B-Device
platter	I-Device
.	O
</s>
<s>
(	O
Sometimes	O
the	O
term	O
side	O
is	O
substituted	O
for	O
head	B-Device
,	O
since	O
platters	B-Device
might	O
be	O
separated	O
from	O
their	O
head	B-Device
assemblies	O
,	O
as	O
with	O
the	O
removable	O
media	O
of	O
a	O
floppy	B-Device
drive	I-Device
.	O
)	O
</s>
<s>
The	O
CHS	O
addressing	O
supported	O
in	O
IBM-PC	O
compatible	O
BIOSes	O
code	O
used	O
eight	O
bits	O
for	O
-	O
theoretically	O
up	O
to	O
256	O
heads	O
counted	O
as	O
head	B-Device
0	O
up	O
to	O
255	O
(	O
FFh	O
)	O
.	O
</s>
<s>
However	O
,	O
a	O
bug	O
in	O
all	O
versions	O
of	O
Microsoft	O
DOS/IBM	O
PC	O
DOS	O
up	O
to	O
and	O
including	O
7.10	O
will	O
cause	O
these	O
operating	B-General_Concept
systems	I-General_Concept
to	O
crash	O
on	O
boot	O
when	O
encountering	O
volumes	O
with	O
256	O
heads	O
.	O
</s>
<s>
This	O
historical	O
oddity	O
can	O
affect	O
the	O
maximum	O
disk	B-Device
size	O
in	O
old	O
BIOS	B-Operating_System
INT	B-Device
13h	I-Device
code	O
as	O
well	O
as	O
old	O
PC	B-Operating_System
DOS	I-Operating_System
or	O
similar	O
operating	B-General_Concept
systems	I-General_Concept
:	O
</s>
<s>
(	O
512	O
bytes/sector	O
)	O
×( 63	O
sectors/track	O
)	O
×( 255	O
heads	O
(	O
tracks/cylinder	O
)	O
)	O
×( 1024	O
cylinders	O
)	O
=	O
8032.5MB	O
,	O
but	O
actually	O
512×63×256×1024	O
=	O
8064MB	O
yields	O
what	O
is	O
known	O
as	O
8	O
GB	O
limit	O
.	O
</s>
<s>
In	O
this	O
context	O
relevant	O
definition	O
of	O
8GB	O
=	O
8192MB	O
is	O
another	O
incorrect	O
limit	O
,	O
because	O
it	O
would	O
require	O
CHS	O
512×64×256	O
with	O
64	O
sectors	O
per	O
track	B-Device
.	O
</s>
<s>
Tracks	B-Device
and	O
cylinders	O
are	O
counted	O
from	O
0	O
,	O
i.e.	O
,	O
track	B-Device
0	O
is	O
the	O
first	O
(	O
outer-most	O
)	O
track	B-Device
on	O
floppy	B-Device
or	O
other	O
cylindrical	O
disks	B-Device
.	O
</s>
<s>
Old	O
BIOS	B-Operating_System
code	O
supported	O
ten	O
bits	O
in	O
CHS	O
addressing	O
with	O
up	O
to	O
1024	O
cylinders	O
(	O
1024	O
=	O
210	O
)	O
.	O
</s>
<s>
Adding	O
six	O
bits	O
for	O
sectors	O
and	O
eight	O
bits	O
for	O
heads	O
results	O
in	O
the	O
24	O
bits	O
supported	O
by	O
BIOS	B-Device
interrupt	I-Device
13h	I-Device
.	O
</s>
<s>
Subtracting	O
the	O
disallowed	O
sector	O
number	O
0	O
in	O
1024×256	O
tracks	B-Device
corresponds	O
to	O
128MB	O
for	O
a	O
sector	O
size	O
of	O
512	O
bytes	B-Application
(	O
128	O
MB	O
=	O
1024×256×( 512	O
byte/sector	O
)	O
)	O
;	O
and	O
8192-128	O
=	O
8064	O
confirms	O
the	O
(	O
roughly	O
)	O
8	O
GB	O
limit	O
.	O
</s>
<s>
In	O
CHS	O
tuples	B-Application
specifying	O
a	O
geometry	O
S	O
actually	O
means	O
sectors	O
per	O
track	B-Device
,	O
and	O
where	O
the	O
(	O
virtual	O
)	O
geometry	O
still	O
matches	O
the	O
capacity	O
the	O
disk	B-Device
contains	O
C×H×S	O
sectors	O
.	O
</s>
<s>
As	O
larger	O
hard	B-Device
disks	I-Device
have	O
come	O
into	O
use	O
,	O
a	O
cylinder	O
has	O
become	O
also	O
a	O
logical	O
disk	B-Device
structure	I-Device
,	O
standardised	O
at	O
16065	O
sectors	O
(	O
16065	O
=	O
255×63	O
)	O
.	O
</s>
<s>
CHS	O
addressing	O
with	O
28	O
bits	O
(	O
EIDE	O
and	O
ATA-2	B-Protocol
)	O
permits	O
eight	O
bits	O
for	O
sectors	O
still	O
starting	O
at	O
1	O
,	O
i.e.	O
,	O
sectors	O
1	O
...	O
255	O
,	O
four	O
bits	O
for	O
heads	O
0	O
...	O
15	O
,	O
and	O
sixteen	O
bits	O
for	O
cylinders	O
0	O
...	O
65535	O
.	O
</s>
<s>
This	O
results	O
in	O
a	O
roughly	O
128	O
GB	O
limit	O
;	O
actually	O
65536×16×255	O
=	O
267386880	O
sectors	O
corresponding	O
to	O
130560MB	O
for	O
a	O
sector	O
size	O
of	O
512	O
bytes	B-Application
.	O
</s>
<s>
The	O
28	O
=	O
16+4+8	O
bits	O
in	O
the	O
ATA-2	B-Protocol
specification	O
are	O
also	O
covered	O
by	O
Ralf	B-Device
Brown	I-Device
's	I-Device
Interrupt	I-Device
List	I-Device
,	O
and	O
an	O
old	O
working	O
draft	O
of	O
this	O
now	O
expired	O
standard	O
was	O
published	O
.	O
</s>
<s>
With	O
an	O
old	O
BIOS	B-Operating_System
limit	O
of	O
1024	O
cylinders	O
and	O
the	O
ATA	B-Protocol
limit	O
of	O
16	O
heads	O
the	O
combined	O
effect	O
was	O
1024×16×63	O
=	O
1032192	O
sectors	O
,	O
i.e.	O
,	O
a	O
504	O
MB	O
limit	O
for	O
sector	O
size	O
512	O
.	O
</s>
<s>
BIOS	B-Operating_System
translation	O
schemes	O
known	O
as	O
ECHS	O
and	O
revised	O
ECHS	O
mitigated	O
this	O
limitation	O
by	O
using	O
128	O
or	O
240	O
instead	O
of	O
16	O
heads	O
,	O
simultaneously	O
reducing	O
the	O
numbers	O
of	O
cylinders	O
and	O
sectors	O
to	O
fit	O
into	O
1024/128/63	O
(	O
ECHS	O
limit	O
:	O
4032MB	O
)	O
or	O
1024/240/63	O
(	O
revised	O
ECHS	O
limit	O
:	O
7560MB	O
)	O
for	O
the	O
given	O
total	O
number	O
of	O
sectors	O
on	O
a	O
disk	B-Device
.	O
</s>
<s>
The	O
Unix	B-Application
communities	O
employ	O
the	O
term	O
block	O
to	O
refer	O
to	O
a	O
sector	O
or	O
group	O
of	O
sectors	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
Linux	O
fdisk	B-Application
utility	O
,	O
before	O
version	O
2.25	O
,	O
displayed	O
partition	B-Application
sizes	O
using	O
1024-byte	O
blocks	O
.	O
</s>
<s>
Clusters	O
are	O
allocation	O
units	O
for	O
data	O
on	O
various	O
file	O
systems	O
(	O
FAT	B-Application
,	O
NTFS	B-Application
,	O
etc	O
.	O
</s>
<s>
Clusters	O
are	O
not	O
directly	O
affected	O
by	O
the	O
physical	O
or	O
virtual	O
geometry	O
of	O
the	O
disk	B-Device
,	O
i.e.	O
,	O
a	O
cluster	O
can	O
begin	O
at	O
a	O
sector	O
near	O
the	O
end	O
of	O
a	O
given	O
CH	O
track	B-Device
,	O
and	O
end	O
in	O
a	O
sector	O
on	O
the	O
physically	O
or	O
logically	O
next	O
CH	O
track	B-Device
.	O
</s>
<s>
In	O
2002	O
the	O
ATA-6	B-Protocol
specification	O
introduced	O
an	O
optional	O
48	O
bits	O
Logical	B-Device
Block	I-Device
Addressing	I-Device
and	O
declared	O
CHS	O
addressing	O
as	O
obsolete	O
,	O
but	O
still	O
allowed	O
to	O
implement	O
the	O
ATA-5	B-Protocol
translations	O
.	O
</s>
<s>
Unsurprisingly	O
the	O
CHS	O
to	O
LBA	O
translation	O
formula	O
given	O
below	O
also	O
matches	O
the	O
last	O
ATA-5	B-Protocol
CHS	O
translation	O
.	O
</s>
<s>
In	O
the	O
ATA-5	B-Protocol
specification	O
CHS	O
support	O
was	O
mandatory	O
for	O
up	O
to	O
16514064	O
sectors	O
and	O
optional	O
for	O
larger	O
disks	B-Device
.	O
</s>
<s>
The	O
ATA-5	B-Protocol
limit	O
corresponds	O
to	O
CHS	O
16383	O
16	O
63	O
or	O
equivalent	O
disk	B-Device
capacities	O
(	O
16514064	O
=	O
16383×16×63	O
=	O
1032×254×63	O
)	O
,	O
and	O
requires	O
24	O
=	O
14+4+6	O
bits	O
(	O
16383	O
+	O
1	O
=	O
214	O
)	O
.	O
</s>
<s>
CHS	O
tuples	B-Application
can	O
be	O
mapped	O
onto	O
LBA	O
addresses	O
using	O
the	O
following	O
formula	O
:	O
</s>
<s>
where	O
A	O
is	O
the	O
LBA	O
address	O
,	O
Nheads	O
is	O
the	O
number	O
of	O
heads	O
on	O
the	O
disk	B-Device
,	O
Nsectors	O
is	O
the	O
maximum	O
number	O
of	O
sectors	O
per	O
track	B-Device
,	O
and	O
(	O
c	O
,	O
h	O
,	O
s	O
)	O
is	O
the	O
CHS	O
address	O
.	O
</s>
<s>
A	O
Logical	O
Sector	O
Number	O
formula	O
in	O
the	O
ECMA-107	O
and	O
ISO/IEC9293:1994	O
(	O
superseding	O
ISO9293:1987	O
)	O
standards	O
for	O
FAT	B-Application
file	I-Application
systems	I-Application
matches	O
exactly	O
the	O
LBA	O
formula	O
given	O
above	O
:	O
Logical	B-Device
Block	I-Device
Address	I-Device
and	O
Logical	O
Sector	O
Number	O
(	O
LSN	O
)	O
are	O
synonyms	O
.	O
</s>
<s>
The	O
formula	O
does	O
not	O
use	O
the	O
number	O
of	O
cylinders	O
,	O
but	O
requires	O
the	O
number	O
of	O
heads	O
and	O
the	O
number	O
of	O
sectors	O
per	O
track	B-Device
in	O
the	O
disk	B-Device
geometry	O
,	O
because	O
the	O
same	O
CHS	O
tuple	B-Application
addresses	O
different	O
logical	O
sector	O
numbers	O
depending	O
on	O
the	O
geometry	O
.	O
</s>
<s>
All	O
the	O
sectors	O
of	O
each	O
head/track	O
get	O
counted	O
before	O
incrementing	O
to	O
the	O
next	O
head/track	O
.	O
</s>
<s>
All	O
the	O
heads/tracks	O
of	O
the	O
same	O
cylinder	O
get	O
counted	O
before	O
incrementing	O
to	O
the	O
next	O
cylinder	O
.	O
</s>
<s>
The	O
outside	O
half	O
of	O
a	O
whole	O
Hard	B-Device
Drive	I-Device
would	O
be	O
the	O
first	O
half	O
of	O
the	O
drive	O
.	O
</s>
<s>
Cylinder	O
Head	B-Device
Record	B-Application
format	I-Application
has	O
been	O
used	O
by	O
Count	B-Application
Key	I-Application
Data	I-Application
(	O
CKD	O
)	O
hard	B-Device
disks	I-Device
on	O
IBM	B-Device
mainframes	I-Device
since	O
at	O
least	O
the	O
1960s	O
.	O
</s>
<s>
This	O
is	O
largely	O
comparable	O
to	O
the	O
Cylinder	B-Device
Head	I-Device
Sector	I-Device
format	O
used	O
by	O
PCs	O
,	O
save	O
that	O
the	O
sector	O
size	O
was	O
not	O
fixed	O
but	O
could	O
vary	O
from	O
track	B-Device
to	O
track	B-Device
based	O
on	O
the	O
needs	O
of	O
each	O
application	O
.	O
</s>
<s>
In	O
contemporary	O
use	O
,	O
the	O
disk	B-Device
geometry	O
presented	O
to	O
the	O
mainframe	O
is	O
emulated	O
by	O
the	O
storage	O
firmware	O
,	O
and	O
no	O
longer	O
has	O
any	O
relation	O
to	O
physical	O
disk	B-Device
geometry	O
.	O
</s>
<s>
Earlier	O
hard	B-Device
drives	I-Device
used	O
in	O
the	O
PC	O
,	O
such	O
as	O
MFM	B-Protocol
and	O
RLL	B-Protocol
drives	O
,	O
divided	O
each	O
cylinder	O
into	O
an	O
equal	O
number	O
of	O
sectors	O
,	O
so	O
the	O
CHS	O
values	O
matched	O
the	O
physical	O
properties	O
of	O
the	O
drive	O
.	O
</s>
<s>
A	O
drive	O
with	O
a	O
CHS	O
tuple	B-Application
of	O
500	O
4	O
32	O
would	O
have	O
500	O
tracks	B-Device
per	O
side	O
on	O
each	O
platter	O
,	O
two	O
platters	B-Device
(	O
4	O
heads	O
)	O
,	O
and	O
32	O
sectors	O
per	O
track	B-Device
,	O
with	O
a	O
total	O
of	O
32768000	O
bytes	B-Application
(	O
31.25MiB	O
)	O
.	O
</s>
<s>
ATA/IDE	B-Protocol
drives	O
were	O
much	O
more	O
efficient	O
at	O
storing	O
data	O
and	O
have	O
replaced	O
the	O
now	O
archaic	O
MFM	B-Protocol
and	O
RLL	B-Protocol
drives	O
.	O
</s>
<s>
They	O
use	O
zone	B-Architecture
bit	I-Architecture
recording	I-Architecture
(	O
ZBR	O
)	O
,	O
where	O
the	O
number	O
of	O
sectors	O
dividing	O
each	O
track	B-Device
varies	O
with	O
the	O
location	O
of	O
groups	O
of	O
tracks	B-Device
on	O
the	O
surface	O
of	O
the	O
platter	O
.	O
</s>
<s>
Tracks	B-Device
nearer	O
to	O
the	O
edge	O
of	O
the	O
platter	O
contain	O
more	O
blocks	O
of	O
data	O
than	O
tracks	B-Device
close	O
to	O
the	O
spindle	O
,	O
because	O
there	O
is	O
more	O
physical	O
space	O
within	O
a	O
given	O
track	B-Device
near	O
the	O
edge	O
of	O
the	O
platter	O
.	O
</s>
<s>
Thus	O
,	O
the	O
CHS	O
addressing	O
scheme	O
cannot	O
correspond	O
directly	O
with	O
the	O
physical	O
geometry	O
of	O
such	O
drives	O
,	O
due	O
to	O
the	O
varying	O
number	O
of	O
sectors	O
per	O
track	B-Device
for	O
different	O
regions	O
on	O
a	O
platter	O
.	O
</s>
<s>
An	O
ATA/IDE	B-Protocol
drive	O
can	O
be	O
set	O
in	O
the	O
system	B-Operating_System
BIOS	I-Operating_System
with	O
any	O
configuration	O
of	O
cylinders	O
,	O
heads	O
and	O
sectors	O
that	O
do	O
not	O
exceed	O
the	O
capacity	O
of	O
the	O
drive	O
(	O
or	O
the	O
BIOS	B-Operating_System
)	O
,	O
since	O
the	O
drive	O
will	O
convert	O
any	O
given	O
CHS	O
value	O
into	O
an	O
actual	O
address	O
for	O
its	O
specific	O
hardware	O
configuration	O
.	O
</s>
<s>
For	O
operating	B-General_Concept
systems	I-General_Concept
such	O
as	O
Microsoft	B-Application
DOS	I-Application
or	O
older	O
version	O
of	O
Windows	B-Application
,	O
each	O
partition	B-Application
must	O
start	O
and	O
end	O
at	O
a	O
cylinder	O
boundary	O
.	O
</s>
<s>
Only	O
some	O
of	O
the	O
most	O
modern	O
operating	B-General_Concept
systems	I-General_Concept
(	O
Windows	B-Application
XP	O
included	O
)	O
may	O
disregard	O
this	O
rule	O
,	O
but	O
doing	O
so	O
can	O
still	O
cause	O
some	O
compatibility	O
issues	O
,	O
especially	O
if	O
the	O
user	O
wants	O
to	O
perform	O
dual	B-Operating_System
booting	I-Operating_System
on	O
the	O
same	O
drive	O
.	O
</s>
<s>
Microsoft	O
does	O
not	O
follow	O
this	O
rule	O
with	O
internal	O
disk	B-Application
partition	I-Application
tools	O
since	O
Windows	B-Application
Vista	O
.	O
</s>
