<s>
Non-volatile	B-General_Concept
memory	I-General_Concept
(	O
NVM	O
)	O
or	O
non-volatile	B-General_Concept
storage	I-General_Concept
is	O
a	O
type	O
of	O
computer	B-General_Concept
memory	I-General_Concept
that	O
can	O
retain	O
stored	O
information	O
even	O
after	O
power	O
is	O
removed	O
.	O
</s>
<s>
In	O
contrast	O
,	O
volatile	B-General_Concept
memory	I-General_Concept
needs	O
constant	O
power	O
in	O
order	O
to	O
retain	O
data	O
.	O
</s>
<s>
Non-volatile	B-General_Concept
memory	I-General_Concept
typically	O
refers	O
to	O
storage	O
in	O
semiconductor	B-Architecture
memory	I-Architecture
chips	O
,	O
which	O
store	O
data	O
in	O
floating-gate	B-Algorithm
memory	B-Algorithm
cells	I-Algorithm
consisting	O
of	O
floating-gate	B-Algorithm
MOSFETs	I-Algorithm
(	O
metal	B-Architecture
–	I-Architecture
oxide	I-Architecture
–	I-Architecture
semiconductor	I-Architecture
field-effect	I-Architecture
transistors	I-Architecture
)	O
,	O
including	O
flash	B-Device
memory	I-Device
storage	I-Device
such	O
as	O
NAND	O
flash	O
and	O
solid-state	B-Device
drives	I-Device
(	O
SSD	B-Device
)	O
.	O
</s>
<s>
Other	O
examples	O
of	O
non-volatile	B-General_Concept
memory	I-General_Concept
include	O
read-only	B-Device
memory	I-Device
(	O
ROM	B-Device
)	O
,	O
EPROM	B-General_Concept
(	O
erasable	B-General_Concept
programmable	I-General_Concept
ROM	I-General_Concept
)	O
and	O
EEPROM	B-General_Concept
(	O
electrically	B-General_Concept
erasable	I-General_Concept
programmable	I-General_Concept
ROM	I-General_Concept
)	O
,	O
ferroelectric	O
RAM	B-Architecture
,	O
most	O
types	O
of	O
computer	B-General_Concept
data	I-General_Concept
storage	I-General_Concept
devices	O
(	O
e.g.	O
</s>
<s>
disk	B-Device
storage	I-Device
,	O
hard	B-Device
disk	I-Device
drives	I-Device
,	O
optical	B-Device
discs	I-Device
,	O
floppy	B-Device
disks	I-Device
,	O
and	O
magnetic	O
tape	O
)	O
,	O
and	O
early	O
computer	B-General_Concept
storage	I-General_Concept
methods	O
such	O
as	O
punched	O
tape	O
and	O
cards	B-Architecture
.	O
</s>
<s>
Non-volatile	B-General_Concept
memory	I-General_Concept
is	O
typically	O
used	O
for	O
the	O
task	O
of	O
secondary	O
storage	O
or	O
long-term	O
persistent	O
storage	O
.	O
</s>
<s>
The	O
most	O
widely	O
used	O
form	O
of	O
primary	O
storage	O
today	O
is	O
a	O
volatile	B-General_Concept
form	O
of	O
random	B-Architecture
access	I-Architecture
memory	I-Architecture
(	O
RAM	B-Architecture
)	O
,	O
meaning	O
that	O
when	O
the	O
computer	O
is	O
shut	O
down	O
,	O
anything	O
contained	O
in	O
RAM	B-Architecture
is	O
lost	O
.	O
</s>
<s>
However	O
,	O
most	O
forms	O
of	O
non-volatile	B-General_Concept
memory	I-General_Concept
have	O
limitations	O
that	O
make	O
them	O
unsuitable	O
for	O
use	O
as	O
primary	O
storage	O
.	O
</s>
<s>
Typically	O
,	O
non-volatile	B-General_Concept
memory	I-General_Concept
costs	O
more	O
,	O
provides	O
lower	O
performance	O
,	O
or	O
has	O
a	O
limited	O
lifetime	O
compared	O
to	O
volatile	B-General_Concept
random	B-Architecture
access	I-Architecture
memory	I-Architecture
.	O
</s>
<s>
Non-volatile	B-General_Concept
data	O
storage	O
can	O
be	O
categorized	O
into	O
electrically	O
addressed	O
systems	O
(	O
read-only	B-Device
memory	I-Device
)	O
and	O
mechanically	O
addressed	O
systems	O
(	O
hard	B-Device
disks	I-Device
,	O
optical	B-Device
disc	I-Device
,	O
magnetic	O
tape	O
,	O
holographic	B-Algorithm
memory	I-Algorithm
,	O
and	O
such	O
)	O
.	O
</s>
<s>
Electrically	O
addressed	O
semiconductor	O
non-volatile	B-General_Concept
memories	I-General_Concept
can	O
be	O
categorized	O
according	O
to	O
their	O
write	O
mechanism	O
.	O
</s>
<s>
Mask	O
ROMs	O
are	O
factory	O
programmable	O
only	O
and	O
typically	O
used	O
for	O
large-volume	O
products	O
which	O
are	O
not	O
required	O
to	O
be	O
updated	O
after	O
the	O
memory	B-General_Concept
device	I-General_Concept
is	O
manufactured	O
.	O
</s>
<s>
Programmable	B-General_Concept
read-only	I-General_Concept
memory	I-General_Concept
(	O
PROM	O
)	O
can	O
be	O
altered	O
once	O
after	O
the	O
memory	B-General_Concept
device	I-General_Concept
is	O
manufactured	O
using	O
a	O
PROM	B-General_Concept
programmer	I-General_Concept
.	O
</s>
<s>
Programming	O
is	O
often	O
done	O
before	O
the	O
device	O
is	O
installed	O
in	O
its	O
target	O
system	O
,	O
typically	O
an	O
embedded	B-Architecture
system	I-Architecture
.	O
</s>
<s>
An	O
EPROM	B-General_Concept
is	O
an	O
erasable	O
ROM	B-Device
that	O
can	O
be	O
changed	O
more	O
than	O
once	O
.	O
</s>
<s>
However	O
,	O
writing	O
new	O
data	O
to	O
an	O
EPROM	B-General_Concept
requires	O
a	O
special	O
programmer	B-General_Concept
circuit	O
.	O
</s>
<s>
EPROMs	B-General_Concept
have	O
a	O
quartz	O
window	O
that	O
allows	O
them	O
to	O
be	O
erased	O
with	O
ultraviolet	O
light	O
,	O
but	O
the	O
whole	O
device	O
is	O
cleared	O
at	O
one	O
time	O
.	O
</s>
<s>
A	O
one-time	B-General_Concept
programmable	I-General_Concept
(	O
OTP	O
)	O
device	O
may	O
be	O
implemented	O
using	O
an	O
EPROM	B-General_Concept
chip	O
without	O
the	O
quartz	O
window	O
;	O
this	O
is	O
less	O
costly	O
to	O
manufacture	O
.	O
</s>
<s>
An	O
electrically	B-General_Concept
erasable	I-General_Concept
programmable	I-General_Concept
read-only	I-General_Concept
memory	I-General_Concept
EEPROM	B-General_Concept
uses	O
voltage	O
to	O
erase	O
memory	O
.	O
</s>
<s>
These	O
erasable	O
memory	B-General_Concept
devices	I-General_Concept
require	O
a	O
significant	O
amount	O
of	O
time	O
to	O
erase	O
data	O
and	O
write	O
new	O
data	O
;	O
they	O
are	O
not	O
usually	O
configured	O
to	O
be	O
programmed	O
by	O
the	O
processor	O
of	O
the	O
target	O
system	O
.	O
</s>
<s>
Data	O
is	O
stored	O
using	O
floating-gate	B-Algorithm
transistors	I-Algorithm
,	O
which	O
require	O
special	O
operating	O
voltages	O
to	O
trap	O
or	O
release	O
electric	O
charge	O
on	O
an	O
insulated	O
control	O
gate	O
to	O
store	O
information	O
.	O
</s>
<s>
Flash	B-Device
memory	I-Device
is	O
a	O
solid-state	O
chip	O
that	O
maintains	O
stored	O
data	O
without	O
any	O
external	O
power	O
source	O
.	O
</s>
<s>
It	O
is	O
a	O
close	O
relative	O
to	O
the	O
EEPROM	B-General_Concept
;	O
it	O
differs	O
in	O
that	O
erase	O
operations	O
must	O
be	O
done	O
on	O
a	O
block	O
basis	O
,	O
and	O
its	O
capacity	O
is	O
substantially	O
larger	O
than	O
that	O
of	O
an	O
EEPROM	B-General_Concept
.	O
</s>
<s>
Flash	B-Device
memory	I-Device
devices	O
use	O
two	O
different	O
technologies	O
—	O
NOR	O
and	O
NAND	O
—	O
to	O
map	O
data	O
.	O
</s>
<s>
Ferroelectric	O
RAM	B-Architecture
(	O
FeRAM	O
,	O
F-RAM	O
or	O
FRAM	O
)	O
is	O
a	O
form	O
of	O
random-access	B-Architecture
memory	I-Architecture
similar	O
in	O
construction	O
to	O
DRAM	O
,	O
both	O
use	O
a	O
capacitor	O
and	O
transistor	O
but	O
instead	O
of	O
using	O
a	O
simple	O
dielectric	O
layer	O
the	O
capacitor	O
,	O
a	O
F-RAM	O
cell	O
contains	O
a	O
thin	O
ferroelectric	O
film	O
of	O
lead	O
zirconate	O
titanate	O
,	O
commonly	O
referred	O
to	O
as	O
PZT	O
.	O
</s>
<s>
Due	O
to	O
the	O
PZT	O
crystal	O
maintaining	O
polarity	O
,	O
F-RAM	O
retains	O
its	O
data	O
memory	O
when	O
power	O
is	O
shut	O
off	O
or	O
interrupted	O
.	O
</s>
<s>
Due	O
to	O
this	O
crystal	O
structure	O
and	O
how	O
it	O
is	O
influenced	O
,	O
F-RAM	O
offers	O
distinct	O
properties	O
from	O
other	O
nonvolatile	B-General_Concept
memory	I-General_Concept
options	O
,	O
including	O
extremely	O
high	O
,	O
although	O
not	O
infinite	O
,	O
endurance	O
(	O
exceeding	O
1016	O
read/write	O
cycles	O
for	O
3.3V	O
devices	O
)	O
,	O
ultra	O
low	O
power	O
consumption	O
(	O
since	O
F-RAM	O
does	O
not	O
require	O
a	O
charge	O
pump	O
like	O
other	O
non-volatile	B-General_Concept
memories	I-General_Concept
)	O
,	O
single-cycle	O
write	O
speeds	O
,	O
and	O
gamma	O
radiation	O
tolerance	O
.	O
</s>
<s>
Magnetoresistive	O
RAM	B-Architecture
stores	O
data	O
in	O
magnetic	O
storage	O
elements	O
called	O
magnetic	O
tunnel	O
junctions	O
(	O
MTJs	O
)	O
.	O
</s>
<s>
The	O
second	O
generation	O
is	O
developed	O
mainly	O
through	O
two	O
approaches	O
:	O
Thermal-assisted	B-General_Concept
switching	I-General_Concept
(	O
TAS	O
)	O
which	O
is	O
being	O
developed	O
by	O
Crocus	O
Technology	O
,	O
and	O
Spin-transfer	B-General_Concept
torque	I-General_Concept
(	O
STT	O
)	O
which	O
Crocus	O
,	O
Hynix	O
,	O
IBM	O
,	O
and	O
several	O
other	O
companies	O
are	O
developing	O
.	O
</s>
<s>
Although	O
ReRAM	O
was	O
initially	O
seen	O
as	O
a	O
replacement	O
technology	O
for	O
flash	B-Device
memory	I-Device
,	O
the	O
cost	O
and	O
performance	O
benefits	O
of	O
ReRAM	O
have	O
not	O
been	O
enough	O
for	O
companies	O
to	O
proceed	O
with	O
the	O
replacement	O
.	O
</s>
<s>
Since	O
the	O
access	O
time	O
depends	O
on	O
the	O
physical	O
location	O
of	O
the	O
data	O
on	O
the	O
device	O
,	O
mechanically	O
addressed	O
systems	O
may	O
be	O
sequential	B-General_Concept
access	I-General_Concept
.	O
</s>
<s>
Hard	B-Device
disk	I-Device
drives	I-Device
use	O
a	O
rotating	O
magnetic	O
disk	B-Device
to	O
store	O
data	O
;	O
access	O
time	O
is	O
longer	O
than	O
for	O
semiconductor	B-Architecture
memory	I-Architecture
,	O
but	O
the	O
cost	O
per	O
stored	O
data	O
bit	O
is	O
very	O
low	O
,	O
and	O
they	O
provide	O
random	O
access	O
to	O
any	O
location	O
on	O
the	O
disk	B-Device
.	O
</s>
<s>
Formerly	O
,	O
removable	O
disk	B-Operating_System
packs	I-Operating_System
were	O
common	O
,	O
allowing	O
storage	B-General_Concept
capacity	I-General_Concept
to	O
be	O
expanded	O
.	O
</s>
<s>
Optical	B-Device
discs	I-Device
store	O
data	O
by	O
altering	O
a	O
pigment	O
layer	O
on	O
a	O
plastic	O
disk	B-Device
and	O
are	O
similarly	O
random	O
access	O
.	O
</s>
<s>
optical	B-Device
jukebox	I-Device
)	O
were	O
used	O
to	O
retrieve	O
and	O
mount	O
disks	B-Device
under	O
direct	O
program	O
control	O
.	O
</s>
<s>
Domain-wall	B-General_Concept
memory	I-General_Concept
(	O
DWM	O
)	O
stores	O
data	O
in	O
a	O
magnetic	O
tunnel	O
junctions	O
(	O
MTJs	O
)	O
,	O
which	O
works	O
by	O
controlling	O
domain	O
wall	O
(	O
DW	O
)	O
motion	O
in	O
ferromagnetic	O
nanowires	O
.	O
</s>
<s>
Thinfilm	O
produces	O
rewriteable	O
non-volatile	B-General_Concept
organic	O
ferroelectric	O
memory	O
based	O
on	O
ferroelectric	O
polymers	O
.	O
</s>
<s>
Each	O
crossing	O
of	O
metal	O
lines	O
is	O
a	O
ferroelectric	O
capacitor	O
and	O
defines	O
a	O
memory	B-Algorithm
cell	I-Algorithm
.	O
</s>
<s>
Non-volatile	B-General_Concept
main	O
memory	O
(	O
NVMM	O
)	O
is	O
primary	O
storage	O
with	O
non-volatile	B-General_Concept
attributes	O
.	O
</s>
<s>
This	O
application	O
of	O
non-volatile	B-General_Concept
memory	I-General_Concept
presents	O
security	O
challenges	O
.	O
</s>
