<s>
The	O
Williams	B-General_Concept
tube	I-General_Concept
,	O
or	O
the	O
Williams	B-General_Concept
–	I-General_Concept
Kilburn	I-General_Concept
tube	I-General_Concept
named	O
after	O
inventors	O
Freddie	O
Williams	O
and	O
Tom	O
Kilburn	O
,	O
is	O
an	O
early	O
form	O
of	O
computer	B-General_Concept
memory	I-General_Concept
.	O
</s>
<s>
It	O
was	O
the	O
first	O
random-access	B-Architecture
digital	O
storage	O
device	O
,	O
and	O
was	O
used	O
successfully	O
in	O
several	O
early	O
computers	O
.	O
</s>
<s>
The	O
Williams	B-General_Concept
tube	I-General_Concept
works	O
by	O
displaying	O
a	O
grid	O
of	O
dots	O
on	O
a	O
cathode-ray	B-Device
tube	I-Device
(	O
CRT	O
)	O
.	O
</s>
<s>
Williams	B-General_Concept
–	I-General_Concept
Kilburn	I-General_Concept
tubes	I-General_Concept
were	O
used	O
primarily	O
on	O
high-speed	O
computer	O
designs	O
.	O
</s>
<s>
The	O
Williams	B-General_Concept
tube	I-General_Concept
depends	O
on	O
an	O
effect	O
called	O
secondary	O
emission	O
that	O
occurs	O
on	O
cathode-ray	B-Device
tubes	I-Device
(	O
CRTs	O
)	O
.	O
</s>
<s>
The	O
process	O
of	O
creating	O
the	O
charge	O
well	O
is	O
used	O
as	O
the	O
write	O
operation	O
in	O
a	O
computer	B-General_Concept
memory	I-General_Concept
,	O
storing	O
a	O
single	O
binary	O
digit	O
,	O
or	O
bit	O
.	O
</s>
<s>
This	O
places	O
an	O
upper	O
limit	O
on	O
the	O
memory	B-Device
density	I-Device
,	O
and	O
each	O
Williams	B-General_Concept
tube	I-General_Concept
could	O
typically	O
store	O
about	O
256	O
to	O
2560	O
bits	O
of	O
data	O
.	O
</s>
<s>
Because	O
the	O
electron	O
beam	O
is	O
essentially	O
inertia-free	O
and	O
can	O
be	O
moved	O
anywhere	O
on	O
the	O
display	O
,	O
the	O
computer	O
can	O
access	O
any	O
location	O
,	O
making	O
it	O
a	O
random	B-Architecture
access	I-Architecture
memory	I-Architecture
.	O
</s>
<s>
Typically	O
,	O
the	O
computer	O
would	O
load	O
the	O
address	O
as	O
an	O
X	O
and	O
Y	O
pair	O
into	O
the	O
driver	O
circuitry	O
and	O
then	O
trigger	O
a	O
time	O
base	O
generator	O
that	O
would	O
sweep	O
the	O
selected	O
locations	O
,	O
reading	O
from	O
or	O
writing	O
to	O
the	O
internal	O
registers	O
,	O
normally	O
implemented	O
as	O
flip-flops	B-General_Concept
.	O
</s>
<s>
As	O
the	O
data	O
is	O
read	O
and	O
then	O
immediately	O
rewritten	O
,	O
this	O
operation	O
can	O
be	O
carried	O
out	O
by	O
external	O
circuitry	O
while	O
the	O
central	B-General_Concept
processing	I-General_Concept
unit	I-General_Concept
(	O
CPU	O
)	O
was	O
busy	O
carrying	O
out	O
other	O
operations	O
.	O
</s>
<s>
This	O
refresh	O
operation	O
is	O
similar	O
to	O
the	O
memory	B-General_Concept
refresh	I-General_Concept
cycles	I-General_Concept
of	O
DRAM	O
in	O
modern	O
systems	O
.	O
</s>
<s>
Some	O
Williams	B-General_Concept
tubes	I-General_Concept
were	O
made	O
from	O
radar-type	O
cathode-ray	B-Device
tubes	I-Device
with	O
a	O
phosphor	O
coating	O
that	O
made	O
the	O
data	O
visible	O
,	O
while	O
other	O
tubes	O
were	O
purpose-built	O
without	O
such	O
a	O
coating	O
.	O
</s>
<s>
Developed	O
at	O
the	O
University	O
of	O
Manchester	O
in	O
England	O
,	O
it	O
provided	O
the	O
medium	O
on	O
which	O
the	O
first	O
electronically	O
stored-memory	O
program	O
was	O
implemented	O
in	O
the	O
Manchester	B-Device
Baby	I-Device
computer	O
,	O
which	O
first	O
successfully	O
ran	O
a	O
program	O
on	O
21	O
June	O
1948	O
.	O
</s>
<s>
In	O
fact	O
,	O
rather	O
than	O
the	O
Williams	B-General_Concept
tube	I-General_Concept
memory	O
being	O
designed	O
for	O
the	O
Baby	O
,	O
the	O
Baby	O
was	O
a	O
testbed	O
to	O
demonstrate	O
the	O
reliability	O
of	O
the	O
memory	O
.	O
</s>
<s>
Williams	B-General_Concept
tubes	I-General_Concept
tended	O
to	O
become	O
unreliable	O
with	O
age	O
,	O
and	O
most	O
working	O
installations	O
had	O
to	O
be	O
"	O
tuned	O
"	O
by	O
hand	O
.	O
</s>
<s>
The	O
Manchester	B-Device
Mark	I-Device
1	I-Device
,	O
which	O
used	O
Williams	B-General_Concept
tubes	I-General_Concept
,	O
was	O
successfully	O
commercialised	O
as	O
the	O
Ferranti	B-Device
Mark	I-Device
1	I-Device
.	O
</s>
<s>
Some	O
early	O
computers	O
in	O
the	O
United	O
States	O
also	O
used	O
Williams	B-General_Concept
tubes	I-General_Concept
,	O
including	O
the	O
IAS	B-Device
machine	I-Device
(	O
originally	O
designed	O
for	O
Selectron	O
tube	O
memory	O
)	O
,	O
the	O
UNIVAC	B-Device
1103	I-Device
,	O
IBM	B-Device
701	I-Device
,	O
IBM	B-Device
702	I-Device
and	O
the	O
Standards	B-Device
Western	I-Device
Automatic	I-Device
Computer	I-Device
(	O
SWAC	B-Device
)	O
.	O
</s>
<s>
Williams	B-General_Concept
tubes	I-General_Concept
were	O
also	O
used	O
in	O
the	O
Soviet	O
Strela-1	B-Device
and	O
in	O
the	O
Japan	O
TAC	O
(	O
Tokyo	O
Automatic	O
Computer	O
)	O
.	O
</s>
