<s>
Millipede	B-General_Concept
memory	I-General_Concept
is	O
a	O
form	O
of	O
non-volatile	B-General_Concept
computer	I-General_Concept
memory	I-General_Concept
.	O
</s>
<s>
It	O
promised	O
a	O
data	B-Device
density	I-Device
of	O
more	O
than	O
1	O
terabit	O
per	O
square	O
inch	O
(	O
1	O
gigabit	O
per	O
square	O
millimeter	O
)	O
,	O
which	O
is	O
about	O
the	O
limit	O
of	O
the	O
perpendicular	B-Device
recording	I-Device
hard	B-Device
drives	I-Device
.	O
</s>
<s>
Millipede	B-General_Concept
storage	O
technology	O
was	O
pursued	O
as	O
a	O
potential	O
replacement	O
for	O
magnetic	B-Architecture
recording	I-Architecture
in	O
hard	B-Device
drives	I-Device
and	O
a	O
means	O
of	O
reducing	O
the	O
physical	O
size	O
of	O
the	O
technology	O
to	O
that	O
of	O
flash	B-Device
media	I-Device
.	O
</s>
<s>
IBM	O
demonstrated	O
a	O
prototype	O
millipede	B-General_Concept
storage	O
device	O
at	O
CeBIT	O
2005	O
,	O
and	O
was	O
trying	O
to	O
make	O
the	O
technology	O
commercially	O
available	O
by	O
the	O
end	O
of	O
2007	O
.	O
</s>
<s>
In	O
contrast	O
,	O
hard	B-Device
drives	I-Device
store	O
data	O
on	O
a	O
disk	O
that	O
is	O
covered	O
with	O
a	O
magnetic	B-Architecture
material	I-Architecture
;	O
data	O
is	O
represented	O
by	O
this	O
material	O
being	O
locally	O
magnetized	O
.	O
</s>
<s>
As	O
a	O
result	O
,	O
a	O
hard	B-Device
drive	I-Device
's	O
performance	O
is	O
limited	O
by	O
the	O
mechanical	O
speed	O
of	O
the	O
motor	O
,	O
and	O
it	O
is	O
generally	O
hundreds	O
of	O
thousands	O
of	O
times	O
slower	O
than	O
DRAM	O
.	O
</s>
<s>
However	O
,	O
since	O
the	O
"	O
cells	O
"	O
in	O
a	O
hard	B-Device
drive	I-Device
are	O
much	O
smaller	O
,	O
the	O
storage	B-Device
density	I-Device
for	O
hard	B-Device
drives	I-Device
is	O
much	O
higher	O
than	O
DRAM	O
.	O
</s>
<s>
Hard	B-Device
drives	I-Device
are	O
non-volatile	B-General_Concept
—	O
data	O
is	O
retained	O
even	O
after	O
power	O
is	O
removed	O
.	O
</s>
<s>
Millipede	B-General_Concept
storage	O
attempts	O
to	O
combine	O
features	O
of	O
both	O
.	O
</s>
<s>
Like	O
a	O
hard	B-Device
drive	I-Device
,	O
millipede	B-General_Concept
both	O
stores	O
data	O
in	O
a	O
medium	O
and	O
accesses	O
the	O
data	O
by	O
moving	O
the	O
medium	O
under	O
the	O
head	O
.	O
</s>
<s>
Also	O
similar	O
to	O
hard	B-Device
drives	I-Device
,	O
millipede	B-General_Concept
's	O
physical	O
medium	O
stores	O
a	O
bit	O
in	O
a	O
small	O
area	O
,	O
leading	O
to	O
high	O
storage	B-Device
densities	I-Device
.	O
</s>
<s>
However	O
,	O
millipede	B-General_Concept
uses	O
many	O
nanoscopic	O
heads	O
that	O
can	O
read	O
and	O
write	O
in	O
parallel	O
,	O
thereby	O
increasing	O
the	O
amount	O
of	O
data	O
read	O
at	O
a	O
given	O
time	O
.	O
</s>
<s>
Mechanically	O
,	O
millipede	B-General_Concept
uses	O
numerous	O
atomic	O
force	O
probes	O
,	O
each	O
of	O
which	O
is	O
responsible	O
for	O
reading	O
and	O
writing	O
a	O
large	O
number	O
of	O
bits	O
associated	O
with	O
it	O
.	O
</s>
<s>
These	O
bits	O
are	O
stored	O
as	O
a	O
pit	O
,	O
or	O
the	O
absence	O
of	O
one	O
,	O
in	O
the	O
surface	O
of	O
a	O
thermo-active	O
polymer	B-Language
,	O
which	O
is	O
deposited	O
as	O
a	O
thin	O
film	O
on	O
a	O
carrier	O
known	O
as	O
the	O
sled	O
.	O
</s>
<s>
These	O
actuators	O
are	O
similar	O
to	O
those	O
that	O
position	O
the	O
read/write	O
head	O
in	O
a	O
typical	O
hard	B-Device
drive	I-Device
,	O
however	O
,	O
the	O
actual	O
distance	O
moved	O
is	O
tiny	O
in	O
comparison	O
.	O
</s>
<s>
Given	O
this	O
layout	O
looked	O
like	O
the	O
legs	O
on	O
a	O
millipede	B-General_Concept
(	O
animal	O
)	O
,	O
the	O
name	O
stuck	O
.	O
</s>
<s>
Regarding	O
the	O
creation	O
of	O
indentations	O
,	O
or	O
pits	O
,	O
non-crosslinked	O
polymers	B-Language
retain	O
a	O
low	O
glass	O
temperature	O
,	O
around	O
120°C	O
for	O
PMMA	O
and	O
if	O
the	O
probe	O
tip	O
is	O
heated	O
to	O
above	O
the	O
glass	O
temperature	O
,	O
it	O
leaves	O
a	O
small	O
indentation	O
.	O
</s>
<s>
By	O
heating	O
the	O
probe	O
immediately	O
next	O
to	O
an	O
indentation	O
,	O
the	O
polymer	B-Language
will	O
re-melt	O
and	O
fill	O
in	O
the	O
indentation	O
,	O
erasing	O
it	O
(	O
see	O
also	O
:	O
thermo-mechanical	O
scanning	O
probe	O
lithography	O
)	O
.	O
</s>
<s>
If	O
each	O
indentation	O
is	O
treated	O
as	O
one	O
bit	O
then	O
a	O
storage	B-Device
density	I-Device
of	O
0.9Tb/in2	O
could	O
theoretically	O
be	O
achieved	O
.	O
</s>
<s>
To	O
write	O
a	O
bit	O
,	O
the	O
tip	O
of	O
the	O
probe	O
is	O
heated	O
to	O
a	O
temperature	O
above	O
the	O
glass	O
transition	O
temperature	O
of	O
the	O
polymer	B-Language
used	O
to	O
manufacture	O
the	O
data	O
sled	O
,	O
which	O
is	O
generally	O
made	O
of	O
acrylic	O
glass	O
.	O
</s>
<s>
To	O
write	O
a	O
"	O
1	O
"	O
,	O
the	O
polymer	B-Language
in	O
proximity	O
to	O
the	O
tip	O
is	O
softened	O
,	O
and	O
then	O
the	O
tip	O
is	O
gently	O
touched	O
to	O
it	O
,	O
causing	O
a	O
dent	O
.	O
</s>
<s>
When	O
operated	O
at	O
data	O
rates	O
of	O
a	O
few	O
megabits	O
per	O
second	O
,	O
Millipede	B-General_Concept
is	O
expected	O
to	O
consume	O
about	O
100	O
milliwatts	O
,	O
which	O
is	O
in	O
the	O
range	O
of	O
flash	B-Device
memory	I-Device
technology	O
and	O
considerably	O
below	O
hard	B-Device
drives	I-Device
.	O
</s>
<s>
However	O
,	O
one	O
of	O
the	O
main	O
advantages	O
of	O
the	O
Millipede	B-General_Concept
design	O
is	O
that	O
it	O
is	O
highly	O
parallel	O
,	O
allowing	O
it	O
to	O
run	O
at	O
much	O
higher	O
speeds	O
into	O
the	O
GB/s	O
.	O
</s>
<s>
At	O
these	O
sorts	O
of	O
speeds	O
one	O
might	O
expect	O
power	O
requirements	O
more	O
closely	O
matching	O
current	O
hard	B-Device
drives	I-Device
,	O
and	O
indeed	O
,	O
data	O
transfer	O
speed	O
is	O
limited	O
to	O
the	O
kilobits-per-second	O
range	O
for	O
an	O
individual	O
probe	O
,	O
which	O
amounts	O
to	O
a	O
few	O
megabits	O
for	O
an	O
entire	O
array	O
.	O
</s>
<s>
Millipede	B-General_Concept
memory	I-General_Concept
was	O
proposed	O
as	O
a	O
form	O
of	O
non-volatile	B-General_Concept
computer	I-General_Concept
memory	I-General_Concept
that	O
was	O
intended	O
to	O
compete	O
with	O
flash	B-Device
memory	I-Device
in	O
terms	O
of	O
data	O
storage	O
,	O
reading	O
and	O
writing	O
speed	O
,	O
and	O
physical	O
size	O
of	O
the	O
technology	O
.	O
</s>
<s>
The	O
earliest	O
generation	O
millipede	B-General_Concept
devices	O
used	O
probes	O
10	O
nanometers	O
in	O
diameter	O
and	O
70	O
nanometers	O
in	O
length	O
,	O
producing	O
pits	O
about	O
40nm	O
in	O
diameter	O
on	O
fields	O
92µm	O
x	O
92µm	O
.	O
</s>
<s>
Arranged	O
in	O
a	O
32	O
x	O
32	O
grid	O
,	O
the	O
resulting	O
3mm	O
x	O
3mm	O
chip	O
stores	O
500	O
megabits	O
of	O
data	O
or	O
62.5	O
MB	O
,	O
resulting	O
in	O
an	O
areal	B-Device
density	I-Device
,	O
the	O
number	O
of	O
bits	O
per	O
square	O
inch	O
,	O
on	O
the	O
order	O
of	O
200	O
Gbit/in²	O
.	O
</s>
<s>
By	O
that	O
point	O
hard	B-Device
drives	I-Device
were	O
approaching	O
150	O
Gbit/in²	O
,	O
and	O
have	O
since	O
surpassed	O
it	O
.	O
</s>
<s>
It	O
appears	O
the	O
pit	O
size	O
can	O
scale	O
to	O
about	O
10nm	O
,	O
resulting	O
in	O
a	O
theoretical	O
areal	B-Device
density	I-Device
just	O
over	O
1Tbit/in²	O
.	O
</s>
<s>
For	O
comparison	O
,	O
as	O
of	O
late	O
2011	O
,	O
laptop	B-Device
hard	I-Device
drives	I-Device
were	O
shipping	O
with	O
a	O
density	O
of	O
636	O
Gbit/in²	O
,	O
and	O
it	O
is	O
expected	O
that	O
heat-assisted	O
magnetic	B-Architecture
recording	I-Architecture
and	O
patterned	O
media	O
together	O
could	O
support	O
densities	O
of	O
10	O
Tbit/in²	O
.	O
</s>
<s>
Flash	B-Device
reached	O
almost	O
250	O
Gbit/in²	O
in	O
early	O
2010	O
.	O
</s>
