<s>
Error	B-Error_Name
correction	I-Error_Name
code	I-Error_Name
memory	O
(	O
ECC	B-General_Concept
memory	I-General_Concept
)	O
is	O
a	O
type	O
of	O
computer	B-General_Concept
data	I-General_Concept
storage	I-General_Concept
that	O
uses	O
an	O
error	B-Error_Name
correction	I-Error_Name
code	I-Error_Name
(	O
ECC	B-Error_Name
)	O
to	O
detect	O
and	O
correct	O
n-bit	O
data	O
corruption	O
which	O
occurs	O
in	O
memory	O
.	O
</s>
<s>
ECC	B-General_Concept
memory	I-General_Concept
is	O
used	O
in	O
most	O
computers	O
where	O
data	O
corruption	O
cannot	O
be	O
tolerated	O
,	O
like	O
industrial	O
control	O
applications	O
,	O
critical	O
databases	O
,	O
and	O
infrastructural	O
memory	O
caches	O
.	O
</s>
<s>
Typically	O
,	O
ECC	B-General_Concept
memory	I-General_Concept
maintains	O
a	O
memory	O
system	O
immune	O
to	O
single-bit	O
errors	O
:	O
the	O
data	O
that	O
is	O
read	O
from	O
each	O
word	O
is	O
always	O
the	O
same	O
as	O
the	O
data	O
that	O
had	O
been	O
written	O
to	O
it	O
,	O
even	O
if	O
one	O
of	O
the	O
bits	O
actually	O
stored	O
has	O
been	O
flipped	O
to	O
the	O
wrong	O
state	O
.	O
</s>
<s>
Most	O
non-ECC	O
memory	O
cannot	O
detect	O
errors	O
,	O
although	O
some	O
non-ECC	O
memory	O
with	O
parity	B-General_Concept
support	O
allows	O
detection	O
but	O
not	O
correction	O
.	O
</s>
<s>
Error	B-Error_Name
correction	I-Error_Name
codes	I-Error_Name
protect	O
against	O
undetected	O
data	O
corruption	O
and	O
are	O
used	O
in	O
computers	O
where	O
such	O
corruption	O
is	O
unacceptable	O
,	O
examples	O
being	O
scientific	O
and	O
financial	O
computing	O
applications	O
,	O
or	O
in	O
database	O
and	O
file	O
servers	O
.	O
</s>
<s>
ECC	B-Error_Name
can	O
also	O
reduce	O
the	O
number	O
of	O
crashes	O
in	O
multi-user	O
server	B-Application
applications	I-Application
and	O
maximum-availability	O
systems	O
.	O
</s>
<s>
It	O
was	O
initially	O
thought	O
that	O
this	O
was	O
mainly	O
due	O
to	O
alpha	O
particles	O
emitted	O
by	O
contaminants	O
in	O
chip	O
packaging	O
material	O
,	O
but	O
research	O
has	O
shown	O
that	O
the	O
majority	O
of	O
one-off	O
soft	O
errors	O
in	O
DRAM	O
chips	O
occur	O
as	O
a	O
result	O
of	O
background	O
radiation	O
,	O
chiefly	O
neutrons	O
from	O
cosmic	O
ray	O
secondaries	O
,	O
which	O
may	O
change	O
the	O
contents	O
of	O
one	O
or	O
more	O
memory	B-Algorithm
cells	I-Algorithm
or	O
interfere	O
with	O
the	O
circuitry	O
used	O
to	O
read	O
or	O
write	O
to	O
them	O
.	O
</s>
<s>
Due	O
to	O
built-in	O
EDAC	B-Error_Name
functionality	O
,	O
the	O
spacecraft	O
's	O
engineering	O
telemetry	O
reported	O
the	O
number	O
of	O
(	O
correctable	O
)	O
single-bit-per-word	O
errors	O
and	O
(	O
uncorrectable	O
)	O
double-bit-per-word	O
errors	O
.	O
</s>
<s>
There	O
was	O
some	O
concern	O
that	O
as	O
DRAM	O
density	O
increases	O
further	O
,	O
and	O
thus	O
the	O
components	O
on	O
chips	O
get	O
smaller	O
,	O
while	O
operating	O
voltages	O
continue	O
to	O
fall	O
,	O
DRAM	O
chips	O
will	O
be	O
affected	O
by	O
such	O
radiation	O
more	O
frequently	O
,	O
since	O
lower-energy	O
particles	O
will	O
be	O
able	O
to	O
change	O
a	O
memory	B-Algorithm
cell	I-Algorithm
's	O
state	O
.	O
</s>
<s>
On	O
the	O
other	O
hand	O
,	O
smaller	O
cells	O
make	O
smaller	O
targets	O
,	O
and	O
moves	O
to	O
technologies	O
such	O
as	O
SOI	B-Algorithm
may	O
make	O
individual	O
cells	O
less	O
susceptible	O
and	O
so	O
counteract	O
,	O
or	O
even	O
reverse	O
,	O
this	O
trend	O
.	O
</s>
<s>
A	O
large-scale	O
study	O
based	O
on	O
Google	B-Application
's	I-Application
very	O
large	O
number	O
of	O
servers	O
was	O
presented	O
at	O
the	O
SIGMETRICS/Performance	O
'	O
09	O
conference	O
.	O
</s>
<s>
More	O
than	O
8%	O
of	O
DIMM	B-General_Concept
memory	O
modules	O
were	O
affected	O
by	O
errors	O
per	O
year	O
.	O
</s>
<s>
In	O
systems	O
without	O
ECC	B-Error_Name
,	O
an	O
error	O
can	O
lead	O
either	O
to	O
a	O
crash	O
or	O
to	O
corruption	O
of	O
data	O
;	O
in	O
large-scale	O
production	O
sites	O
,	O
memory	O
errors	O
are	O
one	O
of	O
the	O
most-common	O
hardware	O
causes	O
of	O
machine	O
crashes	O
.	O
</s>
<s>
Some	O
tests	O
conclude	O
that	O
the	O
isolation	O
of	O
DRAM	O
memory	B-Algorithm
cells	I-Algorithm
can	O
be	O
circumvented	O
by	O
unintended	O
side	O
effects	O
of	O
specially	O
crafted	O
accesses	O
to	O
adjacent	O
cells	O
.	O
</s>
<s>
Thus	O
,	O
accessing	O
data	O
stored	O
in	O
DRAM	O
causes	O
memory	B-Algorithm
cells	I-Algorithm
to	O
leak	O
their	O
charges	O
and	O
interact	O
electrically	O
,	O
as	O
a	O
result	O
of	O
high	O
cell	O
density	O
in	O
modern	O
memory	O
,	O
altering	O
the	O
content	O
of	O
nearby	O
memory	O
rows	O
that	O
actually	O
were	O
not	O
addressed	O
in	O
the	O
original	O
memory	O
access	O
.	O
</s>
<s>
This	O
effect	O
is	O
known	O
as	O
row	B-General_Concept
hammer	I-General_Concept
,	O
and	O
it	O
has	O
also	O
been	O
used	O
in	O
some	O
privilege	O
escalation	O
computer	O
security	O
exploits	O
.	O
</s>
<s>
An	O
example	O
of	O
a	O
single-bit	O
error	O
that	O
would	O
be	O
ignored	O
by	O
a	O
system	O
with	O
no	O
error-checking	O
,	O
would	O
halt	O
a	O
machine	O
with	O
parity	B-General_Concept
checking	O
,	O
or	O
would	O
be	O
invisibly	O
corrected	O
by	O
ECC	B-Error_Name
:	O
a	O
single	O
bit	O
is	O
stuck	O
at	O
1	O
due	O
to	O
a	O
faulty	O
chip	O
,	O
or	O
becomes	O
changed	O
to	O
1	O
due	O
to	O
background	O
or	O
cosmic	O
radiation	O
;	O
a	O
spreadsheet	O
storing	O
numbers	O
in	O
ASCII	O
format	O
is	O
loaded	O
,	O
and	O
the	O
character	O
"	O
8	O
"	O
(	O
decimal	O
value	O
56	O
in	O
the	O
ASCII	O
encoding	O
)	O
is	O
stored	O
in	O
the	O
byte	O
that	O
contains	O
the	O
stuck	O
bit	O
at	O
its	O
lowest	O
bit	O
position	O
;	O
then	O
,	O
a	O
change	O
is	O
made	O
to	O
the	O
spreadsheet	O
and	O
it	O
is	O
saved	O
.	O
</s>
<s>
Several	O
approaches	O
have	O
been	O
developed	O
to	O
deal	O
with	O
unwanted	O
bit-flips	O
,	O
including	O
immunity-aware	O
programming	O
,	O
RAM	B-General_Concept
parity	I-General_Concept
memory	O
,	O
and	O
ECC	B-General_Concept
memory	I-General_Concept
.	O
</s>
<s>
These	O
extra	O
bits	O
are	O
used	O
to	O
record	O
parity	B-General_Concept
or	O
to	O
use	O
an	O
error-correcting	B-Error_Name
code	I-Error_Name
(	O
ECC	B-Error_Name
)	O
.	O
</s>
<s>
Parity	B-General_Concept
allows	O
the	O
detection	O
of	O
all	O
single-bit	O
errors	O
(	O
actually	O
,	O
any	O
odd	O
number	O
of	O
wrong	O
bits	O
)	O
.	O
</s>
<s>
The	O
most-common	O
error	B-Error_Name
correcting	I-Error_Name
code	I-Error_Name
,	O
a	O
single-error	O
correction	O
and	O
double-error	O
detection	O
(	O
SECDED	O
)	O
Hamming	B-Error_Name
code	I-Error_Name
,	O
allows	O
a	O
single-bit	O
error	O
to	O
be	O
corrected	O
and	O
(	O
in	O
the	O
usual	O
configuration	O
,	O
with	O
an	O
extra	O
parity	B-General_Concept
bit	O
)	O
double-bit	O
errors	O
to	O
be	O
detected	O
.	O
</s>
<s>
Chipkill	B-Error_Name
ECC	B-Error_Name
is	O
a	O
more	O
effective	O
version	O
that	O
also	O
corrects	O
for	O
multiple	O
bit	O
errors	O
,	O
including	O
the	O
loss	O
of	O
an	O
entire	O
memory	O
chip	O
.	O
</s>
<s>
Seymour	O
Cray	O
famously	O
said	O
"	O
parity	B-General_Concept
is	O
for	O
farmers	O
"	O
when	O
asked	O
why	O
he	O
left	O
this	O
out	O
of	O
the	O
CDC	B-Device
6600	I-Device
.	O
</s>
<s>
Later	O
,	O
he	O
included	O
parity	B-General_Concept
in	O
the	O
CDC	B-Device
7600	I-Device
,	O
which	O
caused	O
pundits	O
to	O
remark	O
that	O
"	O
apparently	O
a	O
lot	O
of	O
farmers	O
buy	O
computers	O
"	O
.	O
</s>
<s>
The	O
original	O
IBM	B-Device
PC	I-Device
and	O
all	O
PCs	O
until	O
the	O
early	O
1990s	O
used	O
parity	B-General_Concept
checking	O
.	O
</s>
<s>
An	O
ECC-capable	O
memory	O
controller	O
can	O
generally	O
detect	O
and	O
correct	O
errors	O
of	O
a	O
single	O
bit	O
per	O
word	O
(	O
the	O
unit	O
of	O
bus	B-General_Concept
transfer	O
)	O
,	O
and	O
detect	O
(	O
but	O
not	O
correct	O
)	O
errors	O
of	O
two	O
bits	O
per	O
word	O
.	O
</s>
<s>
The	O
BIOS	B-Operating_System
in	O
some	O
computers	O
,	O
when	O
matched	O
with	O
operating	O
systems	O
such	O
as	O
some	O
versions	O
of	O
Linux	B-Application
,	O
BSD	B-Operating_System
,	O
and	O
Windows	O
(	O
Windows	B-Application
2000	I-Application
and	O
later	O
)	O
,	O
allows	O
counting	O
of	O
detected	O
and	O
corrected	O
memory	O
errors	O
,	O
in	O
part	O
to	O
help	O
identify	O
failing	O
memory	O
modules	O
before	O
the	O
problem	O
becomes	O
catastrophic	O
.	O
</s>
<s>
Some	O
DRAM	O
chips	O
include	O
"	O
internal	O
"	O
on-chip	O
error	B-Error_Name
correction	I-Error_Name
circuits	O
,	O
which	O
allow	O
systems	O
with	O
non-ECC	O
memory	O
controllers	O
to	O
still	O
gain	O
most	O
of	O
the	O
benefits	O
of	O
ECC	B-General_Concept
memory	I-General_Concept
.	O
</s>
<s>
In	O
some	O
systems	O
,	O
a	O
similar	O
effect	O
may	O
be	O
achieved	O
by	O
using	O
EOS	B-General_Concept
memory	I-General_Concept
modules	O
.	O
</s>
<s>
Error	B-Error_Name
detection	I-Error_Name
and	I-Error_Name
correction	I-Error_Name
depends	O
on	O
an	O
expectation	O
of	O
the	O
kinds	O
of	O
errors	O
that	O
occur	O
.	O
</s>
<s>
This	O
weakness	O
is	O
addressed	O
by	O
various	O
technologies	O
,	O
including	O
IBM	O
's	O
Chipkill	B-Error_Name
,	O
Sun	O
Microsystems	O
 '	O
Extended	B-Error_Name
ECC	I-Error_Name
,	O
Hewlett	O
Packard	O
's	O
Chipspare	B-Error_Name
,	O
and	O
Intel	O
's	O
Single	B-Error_Name
Device	I-Error_Name
Data	I-Error_Name
Correction	I-Error_Name
(	O
SDDC	O
)	O
.	O
</s>
<s>
DRAM	O
memory	O
may	O
provide	O
increased	O
protection	O
against	O
soft	O
errors	O
by	O
relying	O
on	O
error	B-Error_Name
correcting	I-Error_Name
codes	I-Error_Name
.	O
</s>
<s>
Such	O
error-correcting	B-Error_Name
memory	O
,	O
known	O
as	O
ECC	B-Error_Name
or	O
EDAC-protected	O
memory	O
,	O
is	O
particularly	O
desirable	O
for	O
high	O
fault-tolerant	O
applications	O
,	O
such	O
as	O
servers	O
,	O
as	O
well	O
as	O
deep-space	O
applications	O
due	O
to	O
increased	O
radiation	O
.	O
</s>
<s>
Some	O
systems	O
also	O
"	O
scrub	B-General_Concept
"	O
the	O
memory	O
,	O
by	O
periodically	O
reading	O
all	O
addresses	O
and	O
writing	O
back	O
corrected	O
versions	O
if	O
necessary	O
to	O
remove	O
soft	O
errors	O
.	O
</s>
<s>
As	O
long	O
as	O
a	O
single	O
event	O
upset	O
(	O
SEU	O
)	O
does	O
not	O
exceed	O
the	O
error	O
threshold	O
(	O
e.g.	O
,	O
a	O
single	O
error	O
)	O
in	O
any	O
particular	O
word	O
between	O
accesses	O
,	O
it	O
can	O
be	O
corrected	O
(	O
e.g.	O
,	O
by	O
a	O
single-bit	O
error	B-Error_Name
correcting	I-Error_Name
code	I-Error_Name
)	O
,	O
and	O
an	O
effectively	O
error-free	O
memory	O
system	O
may	O
be	O
maintained	O
.	O
</s>
<s>
Error-correcting	B-Error_Name
memory	O
controllers	O
traditionally	O
use	O
Hamming	B-Error_Name
codes	I-Error_Name
,	O
although	O
some	O
use	O
triple	B-Error_Name
modular	I-Error_Name
redundancy	I-Error_Name
(	O
TMR	O
)	O
.	O
</s>
<s>
The	O
latter	O
is	O
preferred	O
because	O
its	O
hardware	O
is	O
faster	O
than	O
that	O
of	O
Hamming	O
error	B-Error_Name
correction	I-Error_Name
scheme	O
.	O
</s>
<s>
Space	O
satellite	O
systems	O
often	O
use	O
TMR	O
,	O
although	O
satellite	O
RAM	O
usually	O
uses	O
Hamming	O
error	B-Error_Name
correction	I-Error_Name
.	O
</s>
<s>
Many	O
early	O
implementations	O
of	O
ECC	B-General_Concept
memory	I-General_Concept
mask	O
correctable	O
errors	O
,	O
acting	O
"	O
as	O
if	O
"	O
the	O
error	O
never	O
occurred	O
,	O
and	O
only	O
report	O
uncorrectable	O
errors	O
.	O
</s>
<s>
Many	O
ECC	B-General_Concept
memory	I-General_Concept
systems	O
use	O
an	O
"	O
external	O
"	O
EDAC	B-Error_Name
circuit	O
between	O
the	O
CPU	O
and	O
the	O
memory	O
.	O
</s>
<s>
A	O
few	O
systems	O
with	O
ECC	B-General_Concept
memory	I-General_Concept
use	O
both	O
internal	O
and	O
external	O
EDAC	B-Error_Name
systems	O
;	O
the	O
external	O
EDAC	B-Error_Name
system	O
should	O
be	O
designed	O
to	O
correct	O
certain	O
errors	O
that	O
the	O
internal	O
EDAC	B-Error_Name
system	O
is	O
unable	O
to	O
correct	O
.	O
</s>
<s>
Modern	O
desktop	O
and	O
server	O
CPUs	O
integrate	O
the	O
EDAC	B-Error_Name
circuit	O
into	O
the	O
CPU	O
,	O
even	O
before	O
the	O
shift	O
toward	O
CPU-integrated	O
memory	O
controllers	O
,	O
which	O
are	O
related	O
to	O
the	O
NUMA	B-Operating_System
architecture	O
.	O
</s>
<s>
CPU	O
integration	O
enables	O
a	O
zero-penalty	O
EDAC	B-Error_Name
system	O
during	O
error-free	O
operation	O
.	O
</s>
<s>
As	O
of	O
2009	O
,	O
the	O
most-common	O
error-correction	B-Error_Name
codes	O
use	O
Hamming	O
or	O
Hsiao	O
codes	O
that	O
provide	O
single-bit	O
error	B-Error_Name
correction	I-Error_Name
and	O
double-bit	O
error	B-Error_Name
detection	I-Error_Name
(	O
SEC-DED	B-Error_Name
)	O
.	O
</s>
<s>
Other	O
error-correction	B-Error_Name
codes	O
have	O
been	O
proposed	O
for	O
protecting	O
memory	O
double-bit	O
error	O
correcting	O
and	O
triple-bit	O
error	O
detecting	O
(	O
DEC-TED	O
)	O
codes	O
,	O
single-nibble	O
error	O
correcting	O
and	O
double-nibble	O
error	O
detecting	O
(	O
SNC-DND	O
)	O
codes	O
,	O
Reed	B-Error_Name
–	I-Error_Name
Solomon	I-Error_Name
error	I-Error_Name
correction	I-Error_Name
codes	O
,	O
etc	O
.	O
</s>
<s>
However	O
,	O
in	O
practice	O
,	O
multi-bit	O
correction	O
is	O
usually	O
implemented	O
by	O
interleaving	O
multiple	O
SEC-DED	B-Error_Name
codes	O
.	O
</s>
<s>
Early	O
research	O
attempted	O
to	O
minimize	O
the	O
area	O
and	O
delay	O
overheads	O
of	O
ECC	B-Error_Name
circuits	O
.	O
</s>
<s>
Hamming	O
first	O
demonstrated	O
that	O
SEC-DED	B-Error_Name
codes	O
were	O
possible	O
with	O
one	O
particular	O
check	O
matrix	O
.	O
</s>
<s>
Hsiao	O
showed	O
that	O
an	O
alternative	O
matrix	O
with	O
odd	O
weight	O
columns	O
provides	O
SEC-DED	B-Error_Name
capability	O
with	O
less	O
hardware	O
area	O
and	O
shorter	O
delay	O
than	O
traditional	O
Hamming	O
SEC-DED	B-Error_Name
codes	O
.	O
</s>
<s>
Many	O
CPUs	O
use	O
error-correction	B-Error_Name
codes	O
in	O
the	O
on-chip	B-General_Concept
cache	I-General_Concept
,	O
including	O
the	O
Intel	B-General_Concept
Itanium	I-General_Concept
,	O
Xeon	B-Device
,	O
Core	B-Device
and	O
Pentium	B-General_Concept
(	O
since	O
P6	B-Device
microarchitecture	I-Device
)	O
processors	O
,	O
the	O
AMD	B-Architecture
Athlon	I-Architecture
,	O
Opteron	B-General_Concept
,	O
all	O
Zen	O
-	O
and	O
Zen+	O
-based	O
processors	O
(	O
EPYC	O
,	O
EPYC	O
Embedded	O
,	O
Ryzen	O
and	O
Ryzen	O
Threadripper	O
)	O
,	O
and	O
the	O
DEC	O
Alpha	O
21264	O
.	O
</s>
<s>
,	O
EDC/ECC	O
and	O
ECC/ECC	O
are	O
the	O
two	O
most-common	O
cache	O
error-protection	O
techniques	O
used	O
in	O
commercial	O
microprocessors	O
.	O
</s>
<s>
The	O
EDC/ECC	O
technique	O
uses	O
an	O
error-detecting	B-Error_Name
code	I-Error_Name
(	O
EDC	O
)	O
in	O
the	O
level	O
1	O
cache	O
.	O
</s>
<s>
If	O
an	O
error	O
is	O
detected	O
,	O
data	O
is	O
recovered	O
from	O
ECC-protected	O
level	O
2	O
cache	O
.	O
</s>
<s>
The	O
ECC/ECC	O
technique	O
uses	O
an	O
ECC-protected	O
level	O
1	O
cache	O
and	O
an	O
ECC-protected	O
level	O
2	O
cache	O
.	O
</s>
<s>
CPUs	O
that	O
use	O
the	O
EDC/ECC	O
technique	O
always	O
write-through	O
all	O
STOREs	O
to	O
the	O
level	O
2	O
cache	O
,	O
so	O
that	O
when	O
an	O
error	O
is	O
detected	O
during	O
a	O
read	O
from	O
the	O
level	O
1	O
data	B-General_Concept
cache	I-General_Concept
,	O
a	O
copy	O
of	O
that	O
data	O
can	O
be	O
recovered	O
from	O
the	O
level	O
2	O
cache	O
.	O
</s>
<s>
Registered	O
,	O
or	O
buffered	O
,	O
memory	O
is	O
not	O
the	O
same	O
as	O
ECC	B-Error_Name
;	O
the	O
technologies	O
perform	O
different	O
functions	O
.	O
</s>
<s>
It	O
is	O
usual	O
for	O
memory	O
used	O
in	O
servers	O
to	O
be	O
both	O
registered	O
,	O
to	O
allow	O
many	O
memory	O
modules	O
to	O
be	O
used	O
without	O
electrical	O
problems	O
,	O
and	O
ECC	B-Error_Name
,	O
for	O
data	O
integrity	O
.	O
</s>
<s>
However	O
,	O
unbuffered	O
(	O
not-registered	O
)	O
ECC	B-General_Concept
memory	I-General_Concept
is	O
available	O
,	O
and	O
some	O
non-server	O
motherboards	B-Device
support	O
ECC	B-Error_Name
functionality	O
of	O
such	O
modules	O
when	O
used	O
with	O
a	O
CPU	O
that	O
supports	O
ECC	B-Error_Name
.	O
</s>
<s>
Registered	B-General_Concept
memory	I-General_Concept
does	O
not	O
work	O
reliably	O
in	O
motherboards	B-Device
without	O
buffering	O
circuitry	O
,	O
and	O
vice	O
versa	O
.	O
</s>
<s>
ECC	B-General_Concept
memory	I-General_Concept
usually	O
involves	O
a	O
higher	O
price	O
when	O
compared	O
to	O
non-ECC	O
memory	O
,	O
due	O
to	O
additional	O
hardware	O
required	O
for	O
producing	O
ECC	B-General_Concept
memory	I-General_Concept
modules	O
,	O
and	O
due	O
to	O
lower	O
production	O
volumes	O
of	O
ECC	B-General_Concept
memory	I-General_Concept
and	O
associated	O
system	O
hardware	O
.	O
</s>
<s>
Motherboards	B-Device
,	O
chipsets	B-Device
and	O
processors	O
that	O
support	O
ECC	B-Error_Name
may	O
also	O
be	O
more	O
expensive	O
.	O
</s>
<s>
ECC	B-Error_Name
support	O
varies	O
among	O
motherboard	B-Device
manufacturers	O
so	O
ECC	B-General_Concept
memory	I-General_Concept
may	O
simply	O
not	O
be	O
recognized	O
by	O
a	O
ECC-incompatible	O
motherboard	B-Device
.	O
</s>
<s>
Most	O
motherboards	B-Device
and	O
processors	O
for	O
less	O
critical	O
applications	O
are	O
not	O
designed	O
to	O
support	O
ECC	B-Error_Name
.	O
</s>
<s>
Some	O
ECC-enabled	O
boards	O
and	O
processors	O
are	O
able	O
to	O
support	O
unbuffered	O
(	O
unregistered	O
)	O
ECC	B-Error_Name
,	O
but	O
will	O
also	O
work	O
with	O
non-ECC	O
memory	O
;	O
system	O
firmware	O
enables	O
ECC	B-Error_Name
functionality	O
if	O
ECC	B-General_Concept
memory	I-General_Concept
is	O
installed	O
.	O
</s>
<s>
ECC	B-Error_Name
may	O
lower	O
memory	O
performance	O
by	O
around	O
2	O
–	O
3	O
percent	O
on	O
some	O
systems	O
,	O
depending	O
on	O
the	O
application	O
and	O
implementation	O
,	O
due	O
to	O
the	O
additional	O
time	O
needed	O
for	O
ECC	B-General_Concept
memory	I-General_Concept
controllers	O
to	O
perform	O
error	B-Error_Name
checking	I-Error_Name
.	O
</s>
<s>
However	O
,	O
modern	O
systems	O
integrate	O
ECC	B-Error_Name
testing	O
into	O
the	O
CPU	O
,	O
generating	O
no	O
additional	O
delay	O
to	O
memory	O
accesses	O
as	O
long	O
as	O
no	O
errors	O
are	O
detected	O
.	O
</s>
<s>
ECC	B-Error_Name
supporting	O
memory	O
may	O
contribute	O
to	O
additional	O
power	O
consumption	O
due	O
to	O
error	O
correcting	O
circuitry	O
.	O
</s>
