<s>
The	O
IBM	B-Device
System/370	I-Device
Model	I-Device
155	I-Device
(	O
and	O
the	O
Model	B-Device
165	I-Device
)	O
,	O
</s>
<s>
They	O
were	O
the	O
first	O
three	O
models	O
of	O
the	O
IBM	B-Device
System/370	I-Device
line	O
of	O
computers	O
.	O
</s>
<s>
Three	O
months	O
later	O
a	O
fourth	O
IBM	B-Device
System/370	I-Device
,	O
the	O
Model	B-Device
145	I-Device
,	O
was	O
announced	O
.	O
</s>
<s>
Since	O
none	O
of	O
them	O
came	O
with	O
virtual	B-Architecture
memory	I-Architecture
,	O
"	O
which	O
was	O
to	O
be	O
a	O
hallmark	O
of	O
the	O
370	O
line	O
"	O
some	O
said	O
about	O
these	O
early	O
members	O
of	O
the	O
IBM	B-Device
System/370	I-Device
family	O
,	O
especially	O
about	O
the	O
165	O
&	O
155	O
,	O
that	O
they	O
were	O
not	O
"	O
the	O
real	O
370	O
line.	O
"	O
</s>
<s>
"	O
neither	O
offered	O
virtual	B-Architecture
storage	I-Architecture
capability	O
,	O
which	O
was	O
to	O
be	O
a	O
hallmark	O
of	O
the	O
370	O
line.	O
"	O
</s>
<s>
The	O
370/155	O
was	O
described	O
as	O
able	O
to	O
"	O
run	O
under	O
DOS.	O
"	O
</s>
<s>
Both	O
the	O
155	O
and	O
the	O
larger	O
370/165	B-Device
could	O
"	O
run	O
under	O
OS/360.	O
"	O
</s>
<s>
Being	O
members	O
of	O
the	O
System/370	B-Device
family	O
,	O
the	O
Model	O
155	O
and	O
Model	B-Device
165	I-Device
were	O
compatible	O
with	O
each	O
other	O
.	O
</s>
<s>
Neither	O
machine	O
,	O
as	O
announced	O
,	O
could	O
run	O
a	O
virtual	B-Architecture
memory	I-Architecture
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
The	O
initially	O
announced	O
systems	O
were	O
in	O
many	O
ways	O
merely	O
improved	O
IBM	B-Application
360	I-Application
systems	O
.	O
</s>
<s>
running	O
360	O
Operating	B-General_Concept
Systems	I-General_Concept
.	O
</s>
<s>
or	O
new	O
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
The	O
IBM	B-Device
System/370	I-Device
'	O
s	O
basic	O
architecture	B-General_Concept
was	O
described	O
as	O
having	O
been	O
"	O
extended	O
,	O
but	O
not	O
redesigned	O
"	O
from	O
that	O
of	O
IBM	B-Application
System/360	I-Application
.	O
</s>
<s>
In	O
1972	O
an	O
upgrade	O
option	O
was	O
announced	O
"	O
to	O
provide	O
the	O
hardware	O
necessary	O
to	O
operate	O
in	O
a	O
virtual	B-Architecture
memory	I-Architecture
mode.	O
"	O
</s>
<s>
Unlike	O
the	O
IBM	B-Device
System/370	I-Device
Model	I-Device
145	I-Device
,	O
which	O
as	O
early	O
as	O
June	O
1971	O
could	O
have	O
virtual	B-Architecture
memory	I-Architecture
capability	O
added	O
to	O
it	O
with	O
a	O
simple	O
microcode	B-Device
update	O
from	O
a	O
floppy	O
disk	O
,	O
the	O
Model	O
155	O
and	O
Model	B-Device
165	I-Device
needed	O
expensive	O
hardware	O
additions	O
—	O
$	O
200,000	O
for	O
the	O
155	O
and	O
$	O
400,000	O
for	O
the	O
165	O
—	O
to	O
add	O
virtual	B-Architecture
memory	I-Architecture
capability	O
,	O
and	O
even	O
this	O
had	O
to	O
wait	O
until	O
1972	O
,	O
at	O
which	O
time	O
their	O
upgraded	O
155	O
was	O
known	O
as	O
an	O
IBM	O
System/370	O
Model	O
155-II	O
.	O
</s>
<s>
Although	O
the	O
joint	O
155/165	O
announcement	O
did	O
not	O
have	O
the	O
word	O
virtual	O
,	O
there	O
were	O
multiple	O
references	O
to	O
(	O
physical	O
)	O
memory	O
,	O
storage	O
(	O
both	O
main	O
memory	O
and	O
disk	O
storage	O
)	O
,	O
and	O
cache	B-General_Concept
memory	I-General_Concept
under	O
the	O
name	O
"	O
buffer	O
"	O
.	O
</s>
