<s>
Mellon	B-General_Concept
optical	I-General_Concept
memory	I-General_Concept
was	O
an	O
early	O
form	O
of	O
computer	B-General_Concept
memory	I-General_Concept
invented	O
at	O
the	O
Mellon	O
Institute	O
(	O
today	O
part	O
of	O
Carnegie	O
Mellon	O
University	O
)	O
in	O
1951	O
.	O
</s>
<s>
Overall	O
the	O
system	O
was	O
similar	O
to	O
the	O
better-known	O
Williams	B-General_Concept
tube	I-General_Concept
.	O
</s>
<s>
The	O
Williams	B-General_Concept
tube	I-General_Concept
used	O
the	O
phosphorescent	O
front	O
of	O
a	O
single	O
CRT	O
to	O
create	O
small	O
spots	O
of	O
static	O
electricity	O
on	O
a	O
plate	O
arranged	O
in	O
front	O
of	O
the	O
tube	O
.	O
</s>
<s>
Writing	O
to	O
the	O
cell	O
was	O
accomplished	O
by	O
an	O
external	O
cathode	B-Device
ray	I-Device
tube	I-Device
(	O
CRT	O
)	O
arranged	O
in	O
front	O
of	O
the	O
photoemissive	O
side	O
of	O
the	O
grid	O
.	O
</s>
