<s>
Transformer	B-General_Concept
read-only	I-General_Concept
storage	I-General_Concept
(	O
TROS	O
)	O
was	O
a	O
type	O
of	O
read-only	B-Device
memory	I-Device
(	O
ROM	B-Device
)	O
used	O
in	O
the	O
1960s	O
and	O
early	O
1970s	O
before	O
solid-state	O
memory	O
devices	O
were	O
developed	O
.	O
</s>
<s>
TROS	O
was	O
created	O
by	O
IBM	O
as	O
a	O
read-only	B-Device
storage	I-Device
method	O
for	O
storing	O
microcode	B-Device
for	O
IBM	O
computers	O
.	O
</s>
<s>
It	O
was	O
used	O
on	O
the	O
IBM	B-Device
System/360	I-Device
Model	I-Device
20	I-Device
,	O
IBM	B-Device
System/360	I-Device
Model	I-Device
40	I-Device
and	O
the	O
Type	O
2841	O
file	O
control	O
unit	O
.	O
</s>
<s>
TROS	O
memory	O
was	O
used	O
to	O
store	O
microcode	B-Device
for	O
mainframe	B-Architecture
computers	I-Architecture
and	O
intelligent	O
controllers	O
used	O
to	O
control	O
sophisticated	O
storage	O
devices	O
such	O
as	O
disk	O
drives	O
and	O
tape	O
drives	O
.	O
</s>
<s>
If	O
there	O
were	O
a	O
bug	O
in	O
the	O
microcode	B-Device
it	O
was	O
possible	O
to	O
rework	O
it	O
by	O
replacing	O
one	O
or	O
more	O
of	O
the	O
printed	O
wiring	O
sheets	O
,	O
thereby	O
changing	O
the	O
contents	O
of	O
the	O
microcode	B-Device
memory	O
.	O
</s>
