<s>
Magnetic-core	O
memory	O
was	O
the	O
predominant	O
form	O
of	O
random-access	B-General_Concept
computer	B-General_Concept
memory	I-General_Concept
for	O
20	O
years	O
between	O
about	O
1955	O
and	O
1975	O
.	O
</s>
<s>
Such	O
memory	O
is	O
often	O
just	O
called	O
core	B-General_Concept
memory	I-General_Concept
,	O
or	O
,	O
informally	O
,	O
core	O
.	O
</s>
<s>
Core	B-General_Concept
memory	I-General_Concept
uses	O
toroids	O
(	O
rings	O
)	O
of	O
a	O
hard	O
magnetic	O
material	O
(	O
usually	O
a	O
semi-hard	O
ferrite	O
)	O
as	O
transformer	B-Algorithm
cores	O
,	O
where	O
each	O
wire	O
threaded	O
through	O
the	O
core	O
serves	O
as	O
a	O
transformer	B-Algorithm
winding	O
.	O
</s>
<s>
Therefore	O
,	O
they	O
are	O
a	O
type	O
of	O
non-volatile	B-General_Concept
memory	I-General_Concept
.	O
</s>
<s>
Using	O
smaller	O
cores	O
and	O
wires	O
,	O
the	O
memory	B-Device
density	I-Device
of	O
core	O
slowly	O
increased	O
,	O
and	O
by	O
the	O
late	O
1960s	O
a	O
density	O
of	O
about	O
32	O
kilobits	O
per	O
cubic	O
foot	O
(	O
about	O
0.9	O
kilobits	O
per	O
litre	O
)	O
was	O
typical	O
.	O
</s>
<s>
The	O
introduction	O
of	O
the	O
first	O
semiconductor	B-Architecture
memory	I-Architecture
chips	O
in	O
the	O
late	O
1960s	O
,	O
which	O
initially	O
created	O
static	B-Architecture
random-access	I-Architecture
memory	I-Architecture
(	O
SRAM	B-Architecture
)	O
,	O
began	O
to	O
erode	O
the	O
market	O
for	O
core	B-General_Concept
memory	I-General_Concept
.	O
</s>
<s>
The	O
first	O
successful	O
dynamic	O
random-access	B-Architecture
memory	I-Architecture
(	O
DRAM	O
)	O
,	O
the	O
Intel	B-General_Concept
1103	I-General_Concept
,	O
followed	O
in	O
1970	O
.	O
</s>
<s>
Its	O
availability	O
in	O
quantity	O
at	O
1	O
cent	O
per	O
bit	O
marked	O
the	O
beginning	O
of	O
the	O
end	O
for	O
core	B-General_Concept
memory	I-General_Concept
.	O
</s>
<s>
Improvements	O
in	O
semiconductor	B-Architecture
manufacturing	O
led	O
to	O
rapid	O
increases	O
in	O
storage	O
capacity	O
and	O
decreases	O
in	O
price	O
per	O
kilobyte	O
,	O
while	O
the	O
costs	O
and	O
specs	O
of	O
core	B-General_Concept
memory	I-General_Concept
changed	O
little	O
.	O
</s>
<s>
Core	B-General_Concept
memory	I-General_Concept
was	O
driven	O
from	O
the	O
market	O
gradually	O
between	O
1973	O
and	O
1978	O
.	O
</s>
<s>
Depending	O
on	O
how	O
it	O
was	O
wired	O
,	O
core	B-General_Concept
memory	I-General_Concept
could	O
be	O
exceptionally	O
reliable	O
.	O
</s>
<s>
Read-only	B-Device
core	B-General_Concept
rope	I-General_Concept
memory	I-General_Concept
,	O
for	O
example	O
,	O
was	O
used	O
on	O
the	O
mission-critical	O
Apollo	B-Application
Guidance	I-Application
Computer	I-Application
essential	O
to	O
NASA	O
's	O
successful	O
Moon	O
landings	O
.	O
</s>
<s>
Although	O
core	B-General_Concept
memory	I-General_Concept
is	O
obsolete	O
,	O
computer	B-General_Concept
memory	I-General_Concept
is	O
still	O
sometimes	O
called	O
"	O
core	O
"	O
even	O
though	O
it	O
is	O
made	O
of	O
semiconductors	O
,	O
particularly	O
by	O
people	O
who	O
had	O
worked	O
with	O
machines	O
having	O
actual	O
core	B-General_Concept
memory	I-General_Concept
.	O
</s>
<s>
The	O
files	O
that	O
result	O
from	O
saving	O
the	O
entire	O
contents	O
of	O
memory	O
to	O
disk	O
for	O
inspection	O
,	O
which	O
is	O
nowadays	O
commonly	O
performed	O
automatically	O
when	O
a	O
major	O
error	O
occurs	O
in	O
a	O
computer	O
program	O
,	O
are	O
still	O
called	O
"	O
core	B-Error_Name
dumps	I-Error_Name
"	O
.	O
</s>
<s>
Much	O
of	O
this	O
knowledge	O
had	O
developed	O
due	O
to	O
an	O
understanding	O
of	O
transformers	B-Algorithm
,	O
which	O
allowed	O
amplification	O
and	O
switch-like	O
performance	O
when	O
built	O
using	O
certain	O
materials	O
.	O
</s>
<s>
For	O
example	O
,	O
J	O
.	O
Presper	O
Eckert	O
and	O
Jeffrey	O
Chuan	O
Chu	O
had	O
done	O
some	O
development	O
work	O
on	O
the	O
concept	O
in	O
1945	O
at	O
the	O
Moore	O
School	O
during	O
the	O
ENIAC	B-Device
efforts	O
.	O
</s>
<s>
Frederick	O
Viehe	O
applied	O
for	O
various	O
patents	O
on	O
the	O
use	O
of	O
transformers	B-Algorithm
for	O
building	O
digital	O
logic	O
circuits	O
in	O
place	O
of	O
relay	O
logic	O
beginning	O
in	O
1947	O
.	O
</s>
<s>
Substantial	O
work	O
in	O
the	O
field	O
was	O
carried	O
out	O
by	O
the	O
Shanghai-born	O
American	O
physicists	O
An	O
Wang	O
and	O
Way-Dong	O
Woo	O
,	O
who	O
created	O
the	O
pulse	O
transfer	O
controlling	O
device	O
in	O
1949	O
.	O
</s>
<s>
The	O
name	O
referred	O
to	O
the	O
way	O
that	O
the	O
magnetic	O
field	O
of	O
the	O
cores	O
could	O
be	O
used	O
to	O
control	O
the	O
switching	O
of	O
current	O
;	O
his	O
patent	O
focused	O
on	O
using	O
cores	O
to	O
create	O
delay-line	O
or	O
shift-register	B-General_Concept
memory	O
systems	O
.	O
</s>
<s>
The	O
MIT	O
Project	B-Device
Whirlwind	I-Device
computer	O
required	O
a	O
fast	O
memory	O
system	O
for	O
real-time	B-General_Concept
aircraft	O
tracking	O
.	O
</s>
<s>
Several	O
researchers	O
in	O
the	O
late	O
1940s	O
conceived	O
the	O
idea	O
of	O
using	O
magnetic	O
cores	O
for	O
computer	B-General_Concept
memory	I-General_Concept
,	O
but	O
MIT	O
computer	O
engineer	O
Jay	O
Forrester	O
received	O
the	O
principal	O
patent	O
for	O
his	O
invention	O
of	O
the	O
coincident-current	O
core	B-General_Concept
memory	I-General_Concept
that	O
enabled	O
the	O
3D	O
storage	O
of	O
information	O
.	O
</s>
<s>
William	O
Papian	O
of	O
Project	B-Device
Whirlwind	I-Device
cited	O
one	O
of	O
these	O
efforts	O
,	O
Harvard	O
's	O
"	O
Static	O
Magnetic	O
Delay	O
Line	O
"	O
,	O
in	O
an	O
internal	O
memo	O
.	O
</s>
<s>
The	O
first	O
core	B-General_Concept
memory	I-General_Concept
of	O
was	O
installed	O
on	O
Whirlwind	B-Device
in	O
the	O
summer	O
of	O
1953	O
.	O
</s>
<s>
In	O
April	O
2011	O
,	O
Forrester	O
recalled	O
,	O
"	O
the	O
Wang	O
use	O
of	O
cores	O
did	O
not	O
have	O
any	O
influence	O
on	O
my	O
development	O
of	O
random-access	B-Architecture
memory	I-Architecture
.	O
</s>
<s>
Forrester	O
has	O
since	O
observed	O
,	O
"	O
It	O
took	O
us	O
about	O
seven	O
years	O
to	O
convince	O
the	O
industry	O
that	O
random-access	B-General_Concept
magnetic-core	O
memory	O
was	O
the	O
solution	O
to	O
a	O
missing	O
link	O
in	O
computer	O
technology	O
.	O
</s>
<s>
Rajchman	O
later	O
developed	O
versions	O
of	O
the	O
Williams	B-General_Concept
tube	I-General_Concept
and	O
led	O
development	O
of	O
the	O
Selectron	O
.	O
</s>
<s>
Two	O
key	O
inventions	O
led	O
to	O
the	O
development	O
of	O
magnetic	O
core	B-General_Concept
memory	I-General_Concept
in	O
1951	O
.	O
</s>
<s>
The	O
first	O
,	O
An	O
Wang	O
's	O
,	O
was	O
the	O
write-after-read	O
cycle	O
,	O
which	O
solved	O
the	O
problem	O
of	O
how	O
to	O
use	O
a	O
storage	O
medium	O
in	O
which	O
the	O
act	O
of	O
reading	O
erased	O
the	O
data	O
read	O
,	O
enabling	O
the	O
construction	O
of	O
a	O
serial	O
,	O
one-dimensional	O
shift	B-General_Concept
register	I-General_Concept
(	O
of	O
50	O
bits	O
)	O
,	O
using	O
two	O
cores	O
to	O
store	O
a	O
bit	O
.	O
</s>
<s>
A	O
Wang	O
core	O
shift	B-General_Concept
register	I-General_Concept
is	O
in	O
the	O
Revolution	O
exhibit	O
at	O
the	O
Computer	O
History	O
Museum	O
.	O
</s>
<s>
The	O
first	O
use	O
of	O
core	O
was	O
in	O
the	O
Whirlwind	B-Device
computer	I-Device
,	O
and	O
Project	B-Device
Whirlwind	I-Device
's	O
"	O
most	O
famous	O
contribution	O
was	O
the	O
random-access	B-General_Concept
,	O
magnetic	O
core	O
storage	O
feature.	O
"	O
</s>
<s>
Magnetic	O
core	O
was	O
used	O
in	O
peripherals	O
of	O
the	O
ENIAC	B-Device
in	O
1953	O
,	O
the	O
IBM	B-Device
702	I-Device
delivered	O
in	O
July	O
1955	O
,	O
and	O
later	O
in	O
the	O
702	O
itself	O
.	O
</s>
<s>
The	O
IBM	B-Device
704	I-Device
(	O
1954	O
)	O
and	O
the	B-Device
Ferranti	I-Device
Mercury	I-Device
(	O
1957	O
)	O
used	O
magnetic-core	O
memory	O
.	O
</s>
<s>
It	O
was	O
during	O
the	O
early	O
1950s	O
that	O
Seeburg	O
Corporation	O
developed	O
one	O
of	O
the	O
first	O
commercial	O
applications	O
of	O
coincident-current	O
core	B-General_Concept
memory	I-General_Concept
storage	O
in	O
the	O
"	O
Tormat	O
"	O
memory	O
of	O
its	O
new	O
range	O
of	O
jukeboxes	O
,	O
starting	O
with	O
the	O
V200	O
developed	O
in	O
1953	O
and	O
released	O
in	O
1955	O
.	O
</s>
<s>
MIT	O
wanted	O
to	O
charge	O
IBM	O
$0.02	O
per	O
bit	O
royalty	O
on	O
core	B-General_Concept
memory	I-General_Concept
.	O
</s>
<s>
The	O
cost	O
of	O
complete	O
core	B-General_Concept
memory	I-General_Concept
systems	O
was	O
dominated	O
by	O
the	O
cost	O
of	O
stringing	O
the	O
wires	O
through	O
the	O
cores	O
.	O
</s>
<s>
By	O
the	O
early	O
1960s	O
,	O
the	O
cost	O
of	O
core	O
fell	O
to	O
the	O
point	O
that	O
it	O
became	O
nearly	O
universal	O
as	O
main	O
memory	O
,	O
replacing	O
both	O
inexpensive	O
low-performance	O
drum	B-General_Concept
memory	I-General_Concept
and	O
costly	O
high-performance	O
systems	O
using	O
vacuum	O
tubes	O
,	O
and	O
later	O
discrete	O
transistors	B-Application
as	O
memory	O
.	O
</s>
<s>
The	O
cost	O
of	O
core	B-General_Concept
memory	I-General_Concept
declined	O
sharply	O
over	O
the	O
lifetime	O
of	O
the	O
technology	O
:	O
costs	O
began	O
at	O
roughly	O
per	O
bit	O
and	O
dropped	O
to	O
roughly	O
per	O
bit	O
.	O
</s>
<s>
Core	O
was	O
replaced	O
with	O
integrated	O
semiconductor	B-Architecture
RAM	B-Architecture
chips	I-Architecture
in	O
the	O
1970s	O
.	O
</s>
<s>
An	O
example	O
of	O
the	O
scale	O
,	O
economics	O
,	O
and	O
technology	O
of	O
core	B-General_Concept
memory	I-General_Concept
in	O
the	O
1960s	O
was	O
the	O
256K	O
36-bit	O
word	O
(	O
1.2	O
MiB	O
)	O
core	B-General_Concept
memory	I-General_Concept
unit	O
installed	O
on	O
the	O
PDP-6	B-Device
at	O
the	O
MIT	O
Artificial	O
Intelligence	O
Laboratory	O
by	O
1967	O
.	O
</s>
<s>
The	O
term	O
"	O
core	O
"	O
comes	O
from	O
conventional	O
transformers	B-Algorithm
whose	O
windings	O
surround	O
a	O
magnetic	O
core	O
.	O
</s>
<s>
In	O
core	B-General_Concept
memory	I-General_Concept
,	O
the	O
wires	O
pass	O
once	O
through	O
any	O
given	O
corethey	O
are	O
single-turn	O
devices	O
.	O
</s>
<s>
The	O
properties	O
of	O
materials	O
used	O
for	O
memory	O
cores	O
are	O
dramatically	O
different	O
from	O
those	O
used	O
in	O
power	O
transformers	B-Algorithm
.	O
</s>
<s>
The	O
magnetic	O
material	O
for	O
a	O
core	B-General_Concept
memory	I-General_Concept
requires	O
a	O
high	O
degree	O
of	O
magnetic	O
remanence	O
,	O
the	O
ability	O
to	O
stay	O
highly	O
magnetized	O
,	O
and	O
a	O
low	O
coercivity	O
so	O
that	O
less	O
energy	O
is	O
required	O
to	O
change	O
the	O
magnetization	O
direction	O
.	O
</s>
<s>
The	O
core	B-General_Concept
memory	I-General_Concept
contents	O
are	O
retained	O
even	O
when	O
the	O
memory	O
system	O
is	O
powered	O
down	O
(	O
non-volatile	B-General_Concept
memory	I-General_Concept
)	O
.	O
</s>
<s>
Circuits	O
in	O
the	O
computer	B-General_Concept
memory	I-General_Concept
system	O
then	O
restore	O
the	O
information	O
in	O
an	O
immediate	O
re-write	O
cycle	O
.	O
</s>
<s>
The	O
most	O
common	O
form	O
of	O
core	B-General_Concept
memory	I-General_Concept
,	O
X/Y	O
line	O
coincident-current	O
,	O
used	O
for	O
the	O
main	O
memory	O
of	O
a	O
computer	O
,	O
consists	O
of	O
a	O
large	O
number	O
of	O
small	O
toroidal	O
ferrimagnetic	O
ceramic	O
ferrites	O
(	O
cores	O
)	O
held	O
together	O
in	O
a	O
grid	O
structure	O
(	O
organized	O
as	O
a	O
"	O
stack	O
"	O
of	O
layers	O
called	O
planes	O
)	O
,	O
with	O
wires	O
woven	O
through	O
the	O
holes	O
in	O
the	O
cores	O
 '	O
centers	O
.	O
</s>
<s>
Each	O
plane	O
would	O
manipulate	O
one	O
bit	O
of	O
a	O
word	O
in	O
parallel	B-Operating_System
,	O
allowing	O
the	O
full	O
word	O
to	O
be	O
read	O
or	O
written	O
in	O
one	O
cycle	O
.	O
</s>
<s>
To	O
read	O
a	O
bit	O
of	O
core	B-General_Concept
memory	I-General_Concept
,	O
the	O
circuitry	O
tries	O
to	O
flip	O
the	O
bit	O
to	O
the	O
polarity	O
assigned	O
to	O
the	O
0	O
state	O
,	O
by	O
driving	O
the	O
selected	O
X	O
and	O
Y	O
lines	O
that	O
intersect	O
at	O
that	O
core	O
.	O
</s>
<s>
The	O
delay	O
in	O
sensing	O
the	O
voltage	O
pulse	O
is	O
called	O
the	O
access	O
time	O
of	O
the	O
core	B-General_Concept
memory	I-General_Concept
.	O
</s>
<s>
This	O
illustrates	O
why	O
a	O
core	B-General_Concept
memory	I-General_Concept
access	O
is	O
called	O
a	O
destructive	O
read	O
:	O
Any	O
operation	O
that	O
reads	O
the	O
contents	O
of	O
a	O
core	O
erases	O
those	O
contents	O
,	O
and	O
they	O
must	O
immediately	O
be	O
recreated	O
.	O
</s>
<s>
To	O
write	O
a	O
bit	O
of	O
core	B-General_Concept
memory	I-General_Concept
,	O
the	O
circuitry	O
assumes	O
there	O
has	O
been	O
a	O
read	O
operation	O
and	O
the	O
bit	O
is	O
in	O
the	O
0	O
state	O
.	O
</s>
<s>
Core	B-General_Concept
memory	I-General_Concept
controllers	O
were	O
designed	O
so	O
that	O
every	O
read	O
was	O
followed	O
immediately	O
by	O
a	O
write	O
(	O
because	O
the	O
read	O
forced	O
all	O
bits	O
to	O
0	O
,	O
and	O
because	O
the	O
write	O
assumed	O
this	O
had	O
happened	O
)	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
value	O
in	O
memory	O
could	O
be	O
read	O
and	O
incremented	O
(	O
as	O
for	O
example	O
by	O
the	O
AOS	O
instruction	O
on	O
the	O
PDP-6	B-Device
)	O
almost	O
as	O
quickly	O
as	O
it	O
could	O
be	O
read	O
;	O
the	O
hardware	O
simply	O
incremented	O
the	O
value	O
between	O
the	O
read	O
phase	O
and	O
the	O
write	O
phase	O
of	O
a	O
single	O
memory	O
cycle	O
(	O
perhaps	O
signalling	O
the	O
memory	O
controller	O
to	O
pause	O
briefly	O
in	O
the	O
middle	O
of	O
the	O
cycle	O
)	O
.	O
</s>
<s>
Word	O
line	O
core	B-General_Concept
memory	I-General_Concept
was	O
often	O
used	O
to	O
provide	O
register	O
memory	O
.	O
</s>
<s>
This	O
form	O
of	O
core	B-General_Concept
memory	I-General_Concept
typically	O
wove	O
three	O
wires	O
through	O
each	O
core	O
on	O
the	O
plane	O
,	O
word	O
read	O
,	O
word	O
write	O
,	O
and	O
bit	O
sense/write	O
.	O
</s>
<s>
A	O
typical	O
machine	O
's	O
register	O
set	O
usually	O
used	O
only	O
one	O
small	O
plane	O
of	O
this	O
form	O
of	O
core	B-General_Concept
memory	I-General_Concept
.	O
</s>
<s>
Some	O
very	O
large	O
memories	O
were	O
built	O
with	O
this	O
technology	O
,	O
for	O
example	O
the	O
Extended	O
Core	O
Storage	O
(	O
ECS	O
)	O
auxiliary	O
memory	O
in	O
the	O
CDC	B-Device
6600	I-Device
,	O
which	O
was	O
up	O
to	O
2	O
million	O
60-bit	O
words	O
.	O
</s>
<s>
Another	O
form	O
of	O
core	B-General_Concept
memory	I-General_Concept
called	O
core	B-General_Concept
rope	I-General_Concept
memory	I-General_Concept
provided	O
read-only	B-Device
storage	I-Device
.	O
</s>
<s>
In	O
this	O
case	O
,	O
the	O
cores	O
,	O
which	O
had	O
more	O
linear	O
magnetic	O
materials	O
,	O
were	O
simply	O
used	O
as	O
transformers	B-Algorithm
;	O
no	O
information	O
was	O
actually	O
stored	O
magnetically	O
within	O
the	O
individual	O
cores	O
.	O
</s>
<s>
As	O
expected	O
,	O
the	O
cores	O
were	O
much	O
larger	O
physically	O
than	O
those	O
of	O
read-write	O
core	B-General_Concept
memory	I-General_Concept
.	O
</s>
<s>
An	O
example	O
was	O
the	O
Apollo	B-Application
Guidance	I-Application
Computer	I-Application
used	O
for	O
the	O
NASA	O
Moon	O
landings	O
.	O
</s>
<s>
The	O
performance	O
of	O
early	O
core	B-General_Concept
memories	I-General_Concept
can	O
be	O
characterized	O
in	O
today	O
's	O
terms	O
as	O
being	O
very	O
roughly	O
comparable	O
to	O
a	O
clock	O
rate	O
of	O
1	O
MHz	O
(	O
equivalent	O
to	O
early	O
1980s	O
home	O
computers	O
,	O
like	O
the	O
Apple	B-Device
II	I-Device
and	O
Commodore	O
64	O
)	O
.	O
</s>
<s>
Early	O
core	B-General_Concept
memory	I-General_Concept
systems	O
had	O
cycle	O
times	O
of	O
about	O
6	O
µs	O
,	O
which	O
had	O
fallen	O
to	O
1.2	O
µs	O
by	O
the	O
early	O
1970s	O
,	O
and	O
by	O
the	O
mid-70s	O
it	O
was	O
down	O
to	O
600	O
ns	O
(	O
0.6	O
µs	O
)	O
.	O
</s>
<s>
Some	O
designs	O
had	O
substantially	O
higher	O
performance	O
:	O
the	O
CDC	B-Device
6600	I-Device
had	O
a	O
memory	O
cycle	O
time	O
of	O
1.0	O
µs	O
in	O
1964	O
,	O
using	O
cores	O
that	O
required	O
a	O
half-select	O
current	O
of	O
200	O
mA	O
.	O
</s>
<s>
Core	B-General_Concept
memory	I-General_Concept
is	O
non-volatile	B-General_Concept
storage	I-General_Concept
—	O
it	O
can	O
retain	O
its	O
contents	O
indefinitely	O
without	O
power	O
.	O
</s>
<s>
These	O
were	O
important	O
advantages	O
for	O
some	O
applications	O
like	O
first-generation	O
industrial	O
programmable	B-Architecture
controllers	I-Architecture
,	O
military	O
installations	O
and	O
vehicles	O
like	O
fighter	O
aircraft	O
,	O
as	O
well	O
as	O
spacecraft	O
,	O
and	O
led	O
to	O
core	O
being	O
used	O
for	O
a	O
number	O
of	O
years	O
after	O
availability	O
of	O
semiconductor	B-Architecture
MOS	B-Architecture
memory	I-Architecture
(	O
see	O
also	O
MOSFET	B-Architecture
)	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
Space	O
Shuttle	O
IBM	B-Device
AP-101B	I-Device
flight	O
computers	O
used	O
core	B-General_Concept
memory	I-General_Concept
,	O
which	O
preserved	O
the	O
contents	O
of	O
memory	O
even	O
through	O
the	O
Challengers	O
disintegration	O
and	O
subsequent	O
plunge	O
into	O
the	O
sea	O
in	O
1986	O
.	O
</s>
<s>
An	O
example	O
of	O
this	O
is	O
the	O
core	B-General_Concept
memory	I-General_Concept
used	O
by	O
Digital	O
Equipment	O
Corporation	O
for	O
their	O
PDP-1	B-Device
computer	O
;	O
this	O
strategy	O
continued	O
through	O
all	O
of	O
the	O
follow-on	O
core	B-General_Concept
memory	I-General_Concept
systems	O
built	O
by	O
DEC	O
for	O
their	O
PDP	B-Device
line	O
of	O
air-cooled	O
computers	O
.	O
</s>
<s>
Examples	O
of	O
this	O
are	O
the	O
heated-air	O
core	B-General_Concept
memory	I-General_Concept
of	O
the	O
IBM	B-Device
1620	I-Device
(	O
which	O
could	O
take	O
up	O
to	O
30	O
minutes	O
to	O
reach	O
operating	O
temperature	O
,	O
about	O
and	O
the	O
heated-oil-bath	O
core	B-General_Concept
memory	I-General_Concept
of	O
the	O
IBM	B-Device
7090	I-Device
,	O
early	O
IBM	B-Device
7094s	I-Device
,	O
and	O
IBM	B-Device
7030	I-Device
.	O
</s>
<s>
In	O
1980	O
,	O
the	O
price	O
of	O
a	O
16kW	O
(	O
kiloword	O
,	O
equivalent	O
to	O
32	O
kB	O
)	O
core	B-General_Concept
memory	I-General_Concept
board	O
that	O
fitted	O
into	O
a	O
DEC	O
Q-bus	O
computer	O
was	O
around	O
.	O
</s>
<s>
Diagnosing	O
hardware	O
problems	O
in	O
core	B-General_Concept
memory	I-General_Concept
required	O
time-consuming	O
diagnostic	O
programs	O
to	O
be	O
run	O
.	O
</s>
<s>
While	O
a	O
quick	O
test	O
checked	O
if	O
every	O
bit	O
could	O
contain	O
a	O
one	O
and	O
a	O
zero	O
,	O
these	O
diagnostics	O
tested	O
the	O
core	B-General_Concept
memory	I-General_Concept
with	O
worst-case	O
patterns	O
and	O
had	O
to	O
run	O
for	O
several	O
hours	O
.	O
</s>
<s>
As	O
most	O
computers	O
had	O
just	O
a	O
single	O
core	B-General_Concept
memory	I-General_Concept
board	O
,	O
these	O
diagnostics	O
also	O
moved	O
themselves	O
around	O
in	O
memory	O
,	O
making	O
it	O
possible	O
to	O
test	O
every	O
bit	O
.	O
</s>
<s>
The	O
procedure	O
was	O
seldom	O
needed	O
,	O
as	O
core	B-General_Concept
memory	I-General_Concept
proved	O
to	O
be	O
very	O
reliable	O
compared	O
to	O
other	O
computer	O
components	O
of	O
the	O
day	O
.	O
</s>
