<s>
Higher	O
performance	O
in	O
hard	B-Device
disk	I-Device
drives	I-Device
comes	O
from	O
devices	O
which	O
have	O
better	O
performance	O
characteristics	O
.	O
</s>
<s>
The	O
factors	O
that	O
control	O
this	O
time	O
on	O
a	O
rotating	O
drive	O
are	O
mostly	O
related	O
to	O
the	O
mechanical	O
nature	O
of	O
the	O
rotating	O
disks	O
and	O
moving	O
heads	B-Device
.	O
</s>
<s>
Some	O
early	O
PC	O
drives	O
used	O
a	O
stepper	B-Algorithm
motor	I-Algorithm
to	O
move	O
the	O
heads	B-Device
,	O
and	O
as	O
a	O
result	O
had	O
seek	O
times	O
as	O
slow	O
as	O
80	O
–	O
120ms	O
,	O
but	O
this	O
was	O
quickly	O
improved	O
by	O
voice	B-Device
coil	I-Device
type	O
actuation	O
in	O
the	O
1980s	O
,	O
reducing	O
seek	O
times	O
to	O
around	O
20ms	O
.	O
</s>
<s>
Short	O
stroking	O
is	O
a	O
term	O
used	O
in	O
enterprise	O
storage	O
environments	O
to	O
describe	O
an	O
HDD	O
that	O
is	O
purposely	O
restricted	O
in	O
total	O
capacity	O
so	O
that	O
the	O
actuator	O
only	O
has	O
to	O
move	O
the	O
heads	B-Device
across	O
a	O
smaller	O
number	O
of	O
total	O
tracks	O
.	O
</s>
<s>
This	O
limits	O
the	O
maximum	O
distance	O
the	O
heads	B-Device
can	O
be	O
from	O
any	O
point	O
on	O
the	O
drive	O
thereby	O
reducing	O
its	O
average	O
seek	O
time	O
,	O
but	O
also	O
restricts	O
the	O
total	O
capacity	O
of	O
the	O
drive	O
.	O
</s>
<s>
Shorter	O
seek	O
times	O
typically	O
require	O
more	O
energy	O
usage	O
to	O
quickly	O
move	O
the	O
heads	B-Device
across	O
the	O
platter	O
,	O
causing	O
loud	O
noises	O
from	O
the	O
pivot	O
bearing	O
and	O
greater	O
device	O
vibrations	O
as	O
the	O
heads	B-Device
are	O
rapidly	O
accelerated	O
during	O
the	O
start	O
of	O
the	O
seek	O
motion	O
and	O
decelerated	O
at	O
the	O
end	O
of	O
the	O
seek	O
motion	O
.	O
</s>
<s>
Rotational	O
latency	O
(	O
sometimes	O
called	O
rotational	O
delay	O
or	O
just	O
latency	O
)	O
is	O
the	O
delay	O
waiting	O
for	O
the	O
rotation	O
of	O
the	O
disk	O
to	O
bring	O
the	O
required	O
disk	B-Application
sector	I-Application
under	O
the	O
read-write	B-Device
head	I-Device
.	O
</s>
<s>
Maximum	O
rotational	O
latency	O
is	O
the	O
time	O
it	O
takes	O
to	O
do	O
a	O
full	O
rotation	O
excluding	O
any	O
spin-up	B-Device
time	O
(	O
as	O
the	O
relevant	O
part	O
of	O
the	O
disk	O
may	O
have	O
just	O
passed	O
the	O
head	O
when	O
the	O
request	O
arrived	O
)	O
.	O
</s>
<s>
The	O
spindle	O
motor	O
speed	O
can	O
use	O
one	O
of	O
two	O
types	O
of	O
disk	O
rotation	O
methods	O
:	O
1	O
)	O
constant	B-Device
linear	I-Device
velocity	I-Device
(	O
CLV	O
)	O
,	O
used	O
mainly	O
in	O
optical	O
storage	O
,	O
varies	O
the	O
rotational	O
speed	O
of	O
the	O
optical	O
disc	O
depending	O
upon	O
the	O
position	O
of	O
the	O
head	O
,	O
and	O
2	O
)	O
constant	B-Device
angular	I-Device
velocity	I-Device
(	O
CAV	O
)	O
,	O
used	O
in	O
HDDs	O
,	O
standard	O
FDDs	O
,	O
a	O
few	O
optical	O
disc	O
systems	O
,	O
and	O
vinyl	O
audio	O
records	O
,	O
spins	O
the	O
media	O
at	O
one	O
constant	O
speed	O
regardless	O
of	O
where	O
the	O
head	O
is	O
positioned	O
.	O
</s>
<s>
Another	O
wrinkle	O
occurs	O
depending	O
on	O
whether	O
surface	O
bit	B-Device
densities	I-Device
are	O
constant	O
.	O
</s>
<s>
When	O
the	O
bit	B-Device
density	I-Device
is	O
constant	O
,	O
outside	O
tracks	O
have	O
more	O
bits	O
than	O
inside	O
tracks	O
and	O
is	O
generally	O
combined	O
with	O
a	O
CLV	O
spin	O
rate	O
.	O
</s>
<s>
This	O
is	O
not	O
the	O
case	O
with	O
other	O
schemes	O
such	O
as	O
using	O
constant	O
bit	B-Device
density	I-Device
with	O
a	O
CAV	O
spin	O
rate	O
.	O
</s>
<s>
Increasing	O
data	O
center	O
machine	O
density	O
has	O
led	O
to	O
problems	O
delivering	O
sufficient	O
power	O
to	O
devices	O
(	O
especially	O
for	O
spin-up	B-Device
)	O
,	O
and	O
getting	O
rid	O
of	O
the	O
waste	O
heat	O
subsequently	O
produced	O
,	O
as	O
well	O
as	O
environmental	O
and	O
electrical	O
cost	O
concerns	O
(	O
see	O
green	O
computing	O
)	O
.	O
</s>
<s>
Most	O
hard	B-Device
disk	I-Device
drives	I-Device
today	O
support	O
some	O
form	O
of	O
power	O
management	O
which	O
uses	O
a	O
number	O
of	O
specific	O
power	O
modes	O
that	O
save	O
energy	O
by	O
reducing	O
performance	O
.	O
</s>
<s>
Recovery	O
from	O
the	O
deepest	O
mode	O
,	O
typically	O
called	O
Sleep	O
where	O
the	O
drive	O
is	O
stopped	O
or	O
spun	B-Device
down	I-Device
,	O
may	O
take	O
as	O
long	O
as	O
several	O
seconds	O
to	O
be	O
fully	O
operational	O
thereby	O
increasing	O
the	O
resulting	O
latency	O
.	O
</s>
<s>
The	O
drive	O
manufacturers	O
are	O
also	O
now	O
producing	O
green	O
drives	O
that	O
include	O
some	O
additional	O
features	O
that	O
do	O
reduce	O
power	O
,	O
but	O
can	O
adversely	O
affect	O
the	O
latency	O
including	O
lower	O
spindle	O
speeds	O
and	O
parking	O
heads	B-Device
off	O
the	O
media	O
to	O
reduce	O
friction	O
.	O
</s>
<s>
The	O
is	O
the	O
time	O
it	O
takes	O
the	O
heads	B-Device
to	O
settle	O
on	O
the	O
target	O
track	O
and	O
stop	O
vibrating	O
so	O
they	O
do	O
not	O
read	O
or	O
write	O
off	O
track	O
.	O
</s>
<s>
The	O
sustained	O
rate	O
is	O
less	O
than	O
or	O
equal	O
to	O
the	O
maximum	O
or	O
burst	O
rate	O
because	O
it	O
does	O
not	O
have	O
the	O
benefit	O
of	O
any	O
cache	O
or	O
buffer	B-Device
memory	O
in	O
the	O
drive	O
.	O
</s>
<s>
According	O
to	O
vendor	O
specifications	O
sustained	O
transfer	O
rates	O
up	O
to	O
204MB/s	O
are	O
available.https://www.seagate.com/files/docs/pdf/datasheet/disc/cheetah	O
-15k.7-ds1677.3-1007us.pdf	O
,	O
a	O
typical	O
7,200	O
RPM	O
desktop	O
HDD	O
has	O
a	O
"	O
disk-to-buffer	O
"	O
data	O
transfer	O
rate	O
up	O
to	O
1030	O
Mbit/s	O
.	O
</s>
<s>
Floppy	O
disk	O
drives	O
have	O
sustained	O
"	O
disk-to-buffer	O
"	O
data	O
transfer	O
rates	O
that	O
are	O
one	O
or	O
two	O
orders	O
of	O
magnitude	O
lower	O
than	O
that	O
of	O
HDDs	O
.	O
</s>
<s>
The	O
sustained	O
"	O
disk-to-buffer	O
"	O
data	O
transfer	O
rates	O
varies	O
amongst	O
families	O
of	O
Optical	O
disk	O
drives	O
with	O
the	O
slowest	O
1x	O
CDs	O
at	O
1.23	O
Mbit/s	O
floppy-like	O
while	O
a	O
high	O
performance	O
12x	O
Blu-ray	O
drive	O
at	O
432	O
Mbit/s	O
approaches	O
the	O
performance	O
of	O
HDDs	O
.	O
</s>
<s>
A	O
current	O
widely	O
used	O
standard	O
for	O
the	O
"	O
buffer-to-computer	O
"	O
interface	O
is	O
3.0	O
Gbit/s	O
SATA	O
,	O
which	O
can	O
send	O
about	O
300	O
megabyte/s	O
(	O
10-bit	O
encoding	O
)	O
from	O
the	O
buffer	B-Device
to	O
the	O
computer	O
,	O
and	O
thus	O
is	O
still	O
comfortably	O
ahead	O
of	O
today	O
's	O
disk-to-buffer	O
transfer	O
rates	O
.	O
</s>
<s>
SSDs	B-Device
do	O
not	O
have	O
the	O
same	O
internal	O
limits	O
of	O
HDDs	O
,	O
so	O
their	O
internal	O
and	O
external	O
transfer	O
rates	O
are	O
often	O
maximizing	O
the	O
capabilities	O
of	O
the	O
drive-to-host	O
interface	O
.	O
</s>
<s>
Transfer	O
rate	O
can	O
be	O
influenced	O
by	O
file	B-Application
system	I-Application
fragmentation	I-Application
and	O
the	O
layout	O
of	O
the	O
files	O
.	O
</s>
<s>
Defragmentation	B-Application
is	O
a	O
procedure	O
used	O
to	O
minimize	O
delay	O
in	O
retrieving	O
data	O
by	O
moving	O
related	O
items	O
to	O
physically	O
proximate	O
areas	O
on	O
the	O
disk	O
.	O
</s>
<s>
Some	O
computer	O
operating	O
systems	O
perform	O
defragmentation	B-Application
automatically	O
.	O
</s>
<s>
Although	O
automatic	O
defragmentation	B-Application
is	O
intended	O
to	O
reduce	O
access	O
delays	O
,	O
the	O
procedure	O
can	O
slow	O
response	O
when	O
performed	O
while	O
the	O
computer	O
is	O
in	O
use	O
.	O
</s>
<s>
Improvement	O
of	O
data	O
transfer	O
rate	O
performance	O
is	O
correlated	O
to	O
the	O
areal	B-Device
density	I-Device
only	O
by	O
increasing	O
a	O
track	O
's	O
linear	O
surface	O
bit	B-Device
density	I-Device
(	O
sectors	O
per	O
track	O
)	O
.	O
</s>
<s>
According	O
to	O
industry	O
observers	O
and	O
analysts	O
for	O
2011	O
to	O
2016	O
,	O
“	O
The	O
current	O
roadmap	O
predicts	O
no	O
more	O
than	O
a	O
20%	O
/yr	O
improvement	O
in	O
bit	B-Device
density	I-Device
”	O
.	O
</s>
<s>
Seek	O
times	O
have	O
not	O
kept	O
up	O
with	O
throughput	O
increases	O
,	O
which	O
themselves	O
have	O
not	O
kept	O
up	O
with	O
growth	O
in	O
bit	B-Device
density	I-Device
and	O
storage	O
capacity	O
.	O
</s>
<s>
Interleaving	B-Application
introduced	O
gaps	O
between	O
data	O
sectors	O
to	O
allow	O
time	O
for	O
slow	O
equipment	O
to	O
get	O
ready	O
to	O
read	O
the	O
next	O
block	O
of	O
data	O
.	O
</s>
<s>
Without	O
interleaving	B-Application
,	O
the	O
next	O
logical	O
sector	O
would	O
arrive	O
at	O
the	O
read/write	B-Device
head	I-Device
before	O
the	O
equipment	O
was	O
ready	O
,	O
requiring	O
the	O
system	O
to	O
wait	O
for	O
another	O
complete	O
disk	O
revolution	O
before	O
reading	O
could	O
be	O
performed	O
.	O
</s>
<s>
However	O
,	O
because	O
interleaving	B-Application
introduces	O
intentional	O
physical	O
delays	O
between	O
blocks	O
of	O
data	O
thereby	O
lowering	O
the	O
data	O
rate	O
,	O
setting	O
the	O
interleave	O
to	O
a	O
ratio	O
higher	O
than	O
required	O
causes	O
unnecessary	O
delays	O
for	O
equipment	O
that	O
has	O
the	O
performance	O
needed	O
to	O
read	O
sectors	O
more	O
quickly	O
.	O
</s>
<s>
The	O
interleaving	B-Application
ratio	O
was	O
therefore	O
usually	O
chosen	O
by	O
the	O
end-user	O
to	O
suit	O
their	O
particular	O
computer	O
system	O
's	O
performance	O
capabilities	O
when	O
the	O
drive	O
was	O
first	O
installed	O
in	O
their	O
system	O
.	O
</s>
<s>
Modern	O
technology	O
is	O
capable	O
of	O
reading	O
data	O
as	O
fast	O
as	O
it	O
can	O
be	O
obtained	O
from	O
the	O
spinning	O
platters	O
,	O
so	O
interleaving	B-Application
is	O
no	O
longer	O
used	O
.	O
</s>
<s>
Many	O
of	O
the	O
hard	B-Device
drive	I-Device
companies	O
are	O
now	O
producing	O
Green	O
Drives	O
that	O
require	O
much	O
less	O
power	O
and	O
cooling	O
.	O
</s>
<s>
Power	O
consumption	O
can	O
also	O
be	O
reduced	O
by	O
parking	O
the	O
drive	B-Device
heads	I-Device
when	O
the	O
disk	O
is	O
not	O
in	O
use	O
reducing	O
friction	O
,	O
adjusting	O
spin	O
speeds	O
,	O
and	O
disabling	O
internal	O
components	O
when	O
not	O
in	O
use	O
.	O
</s>
<s>
Drives	O
use	O
more	O
power	O
,	O
briefly	O
,	O
when	O
starting	O
up	O
(	O
spin-up	B-Device
)	O
.	O
</s>
<s>
On	O
SCSI	O
hard	B-Device
disk	I-Device
drives	I-Device
,	O
the	O
SCSI	O
controller	O
can	O
directly	O
control	O
spin	O
up	O
and	O
spin	O
down	O
of	O
the	O
drives	O
.	O
</s>
<s>
Some	O
Parallel	B-Protocol
ATA	I-Protocol
(	O
PATA	B-Protocol
)	O
and	O
Serial	O
ATA	O
(	O
SATA	O
)	O
hard	B-Device
disk	I-Device
drives	I-Device
support	O
power-up	O
in	O
standby	O
(	O
PUIS	O
)	O
:	O
each	O
drive	O
does	O
not	O
spin	O
up	O
until	O
the	O
controller	O
or	O
system	O
BIOS	O
issues	O
a	O
specific	O
command	O
to	O
do	O
so	O
.	O
</s>
<s>
Some	O
SATAII	O
and	O
later	O
hard	B-Device
disk	I-Device
drives	I-Device
support	O
staggered	O
spin-up	B-Device
,	O
allowing	O
the	O
computer	O
to	O
spin	O
up	O
the	O
drives	O
in	O
sequence	O
to	O
reduce	O
load	O
on	O
the	O
power	O
supply	O
when	O
booting	O
.	O
</s>
<s>
Most	O
hard	B-Device
disk	I-Device
drives	I-Device
today	O
support	O
some	O
form	O
of	O
power	O
management	O
which	O
uses	O
a	O
number	O
of	O
specific	O
power	O
modes	O
that	O
save	O
energy	O
by	O
reducing	O
performance	O
.	O
</s>
<s>
Some	O
laptops	O
now	O
include	O
active	B-Device
hard	I-Device
drive	I-Device
protection	I-Device
that	O
parks	O
the	O
disk	B-Device
heads	I-Device
if	O
the	O
machine	O
is	O
dropped	O
,	O
hopefully	O
before	O
impact	O
,	O
to	O
offer	O
the	O
greatest	O
possible	O
chance	O
of	O
survival	O
in	O
such	O
an	O
event	O
.	O
</s>
<s>
Hard	B-Device
drives	I-Device
that	O
use	O
shingled	B-Device
magnetic	I-Device
recording	I-Device
(	O
SMR	O
)	O
differ	O
significantly	O
in	O
write	O
performance	O
characteristics	O
from	O
conventional	O
(	O
CMR	O
)	O
drives	O
.	O
</s>
<s>
Solid-state	B-Device
devices	I-Device
(	O
SSDs	B-Device
)	O
do	O
not	O
have	O
moving	O
parts	O
.	O
</s>
<s>
Typical	O
SSDs	B-Device
will	O
have	O
a	O
seek	O
time	O
between	O
0.08	O
and	O
0.16ms	O
.	O
</s>
<s>
Flash	O
memory-based	O
SSDs	B-Device
do	O
not	O
need	O
defragmentation	B-Application
.	O
</s>
<s>
However	O
,	O
because	O
file	O
systems	O
write	B-Error_Name
pages	I-Error_Name
of	I-Error_Name
data	I-Error_Name
that	O
are	O
smaller	O
(	O
2K	O
,	O
4K	O
,	O
8K	O
,	O
or	O
16K	O
)	O
than	O
the	O
blocks	O
of	O
data	O
managed	O
by	O
the	O
SSD	B-Device
(	O
from	O
256KB	O
to	O
4MB	O
,	O
hence	O
128	O
to	O
256	O
pages	O
per	O
block	O
)	O
,	O
over	O
time	O
,	O
an	O
SSD	B-Device
's	O
write	O
performance	O
can	O
degrade	O
as	O
the	O
drive	O
becomes	O
full	O
of	O
pages	O
which	O
are	O
partial	O
or	O
no	O
longer	O
needed	O
by	O
the	O
file	O
system	O
.	O
</s>
<s>
Flash	O
memory	O
wears	O
out	O
over	O
time	O
as	O
it	O
is	O
repeatedly	O
written	O
to	O
;	O
the	O
writes	O
required	O
by	O
defragmentation	B-Application
wear	O
the	O
drive	O
for	O
no	O
speed	O
advantage	O
.	O
</s>
