<s>
Digital	B-General_Concept
permanence	I-General_Concept
addresses	O
the	O
history	O
and	O
development	O
of	O
digital	B-General_Concept
storage	I-General_Concept
techniques	O
,	O
specifically	O
quantifying	O
the	O
expected	O
lifetime	O
of	O
data	O
stored	O
on	O
various	O
digital	O
media	O
and	O
the	O
factors	O
which	O
influence	O
the	O
permanence	O
of	O
digital	O
data	O
.	O
</s>
<s>
This	O
article	O
describes	O
how	O
reliable	O
different	O
types	O
of	O
storage	B-General_Concept
media	I-General_Concept
are	O
at	O
storing	O
data	O
over	O
time	O
and	O
factors	O
affecting	O
this	O
reliability	O
.	O
</s>
<s>
Librarians	B-Application
and	O
archivists	O
responsible	O
for	O
large	O
repositories	O
of	O
information	O
take	O
a	O
deeper	O
view	O
of	O
electronic	O
archives	O
.	O
</s>
<s>
Data	B-Device
format	I-Device
Data	O
must	O
be	O
stored	O
in	O
a	O
format	O
which	O
can	O
be	O
meaningfully	O
accessed	O
now	O
and	O
in	O
the	O
future	O
.	O
</s>
<s>
Digital	O
computers	O
,	O
in	O
particular	O
,	O
make	O
use	O
of	O
two	O
forms	O
of	O
memory	B-General_Concept
known	O
as	O
RAM	B-Architecture
or	O
ROM	B-Device
and	O
although	O
the	O
most	O
common	O
form	O
today	O
is	O
RAM	B-Architecture
,	O
designed	O
to	O
retain	O
data	O
while	O
the	O
computer	O
is	O
powered	O
on	O
,	O
this	O
was	O
not	O
always	O
the	O
case	O
.	O
</s>
<s>
Nor	O
is	O
active	O
memory	B-General_Concept
the	O
only	O
form	O
used	O
;	O
passive	O
memory	B-General_Concept
devices	I-General_Concept
are	O
now	O
in	O
common	O
use	O
in	O
digital	O
cameras	O
.	O
</s>
<s>
PROM	B-General_Concept
,	O
or	O
programmable	B-General_Concept
read-only	I-General_Concept
memory	I-General_Concept
,	O
stores	O
data	O
in	O
a	O
fixed	O
form	O
during	O
the	O
manufacturing	O
process	O
,	O
with	O
data	O
retention	O
dependent	O
on	O
the	O
life	O
expectancy	O
of	O
the	O
device	O
itself	O
.	O
</s>
<s>
EPROM	B-General_Concept
,	O
or	O
erasable	B-General_Concept
programmable	I-General_Concept
read-only	I-General_Concept
memory	I-General_Concept
,	O
is	O
similar	O
to	O
PROM	B-General_Concept
but	O
can	O
be	O
cleared	O
by	O
exposure	O
to	O
ultraviolet	B-Application
light	O
.	O
</s>
<s>
EEPROM	B-General_Concept
,	O
or	O
electrically	B-General_Concept
erasable	I-General_Concept
programmable	I-General_Concept
read-only	I-General_Concept
memory	I-General_Concept
,	O
is	O
the	O
format	O
used	O
by	O
flash	B-Device
memory	I-Device
devices	O
and	O
can	O
be	O
erased	O
and	O
rewritten	O
electronically	O
.	O
</s>
<s>
optical	B-Device
media	I-Device
(	O
rotating	O
media	O
combined	O
with	O
a	O
moveable	O
read/write	O
head	O
comprising	O
a	O
laser	O
)	O
,	O
such	O
as	O
:	O
</s>
<s>
Write	B-Device
once	I-Device
read	I-Device
many	I-Device
(	O
WORM	B-Device
)	O
media	O
such	O
as	O
CD-R	O
,	O
DVD±R	O
,	O
BD-R	B-Operating_System
.	O
</s>
<s>
Rewriteable	O
media	O
such	O
as	O
CD-RW	O
,	O
DVD±RW	O
,	O
BD-RE	B-Operating_System
.	O
</s>
<s>
Although	O
not	O
a	O
digital	B-General_Concept
storage	I-General_Concept
medium	O
in	O
itself	O
,	O
printing	O
hard-copies	O
of	O
documents	O
and	O
images	O
remains	O
a	O
popular	O
means	O
of	O
representing	O
digital	O
data	O
and	O
possibly	O
acquires	O
the	O
qualities	O
associated	O
with	O
original	O
documents	O
especially	O
their	O
potential	O
for	O
endurance	O
.	O
</s>
<s>
The	O
short-comings	O
of	O
some	O
storage	B-General_Concept
media	I-General_Concept
is	O
already	O
well	O
recognised	O
and	O
various	O
attempts	O
have	O
been	O
made	O
to	O
supplement	O
the	O
permanence	O
of	O
an	O
under-lying	O
technology	O
.	O
</s>
<s>
These	O
"	O
soft	O
storage	O
technologies	O
"	O
enhance	O
their	O
base	O
technology	O
by	O
applying	O
software	O
or	O
system	O
techniques	O
often	O
within	O
quite	O
narrow	O
fields	O
of	O
data	B-General_Concept
storage	I-General_Concept
and	O
not	O
always	O
with	O
the	O
explicit	O
intention	O
of	O
improving	O
digital	B-General_Concept
permanence	I-General_Concept
.	O
</s>
