<s>
The	O
IBM	B-Operating_System
3270	I-Operating_System
PC	O
(	O
IBM	O
System	O
Unit	O
5271	O
)	O
,	O
released	O
in	O
October	O
1983	O
,	O
is	O
an	O
IBM	B-Device
PC	I-Device
XT	I-Device
containing	O
additional	O
hardware	O
that	O
,	O
in	O
combination	O
with	O
software	O
,	O
can	O
emulate	B-Application
the	O
behaviour	O
of	O
an	O
IBM	B-Operating_System
3270	I-Operating_System
terminal	O
.	O
</s>
<s>
It	O
can	O
therefore	O
be	O
used	O
both	O
as	O
a	O
standalone	O
computer	O
,	O
and	O
as	O
a	O
terminal	O
to	O
a	O
mainframe	B-Architecture
.	O
</s>
<s>
IBM	O
later	O
released	O
the	O
3270	B-Operating_System
AT	O
(	O
IBM	O
System	O
Unit	O
5273	O
)	O
,	O
which	O
is	O
a	O
similar	O
design	O
based	O
on	O
the	O
IBM	B-Operating_System
PC	I-Operating_System
AT	I-Operating_System
.	O
</s>
<s>
They	O
also	O
released	O
high-end	O
graphics	O
versions	O
of	O
the	O
3270	B-Operating_System
PC	O
in	O
both	O
XT	O
and	O
AT	O
variants	O
.	O
</s>
<s>
The	O
XT-based	O
versions	O
are	O
called	O
3270	B-Operating_System
PC/G	O
and	O
3270	B-Operating_System
PC/GX	O
and	O
they	O
use	O
a	O
different	O
System	O
Unit	O
5371	O
,	O
while	O
their	O
AT	O
counterparts	O
(	O
PC	O
AT/G	O
and	O
PC	O
AT/GX	O
)	O
have	O
System	O
Unit	O
5373	O
.	O
</s>
<s>
It	O
includes	O
a	O
video	B-Device
card	I-Device
which	O
occupies	O
1-3	O
ISA	B-Architecture
slots	I-Architecture
(	O
depending	O
on	O
what	O
level	O
of	O
graphics	O
support	O
is	O
required	O
)	O
,	O
and	O
supports	O
CGA	B-Device
and	O
MDA	B-Device
video	O
modes	O
.	O
</s>
<s>
The	O
display	O
resolution	O
is	O
720×350	O
,	O
either	O
on	O
the	O
matching	O
14-inch	O
color	O
monitor	O
(	O
model	O
5272	O
)	O
or	O
in	O
monochrome	O
on	O
an	O
MDA	B-Device
monitor	O
.	O
</s>
<s>
A	O
further	O
expansion	O
card	O
intercepts	O
scancodes	O
from	O
the	O
122-key	O
3270	B-Operating_System
keyboard	O
,	O
translating	O
them	O
into	O
XT	O
scancodes	O
which	O
are	O
then	O
sent	O
to	O
the	O
normal	O
keyboard	O
connector	O
.	O
</s>
<s>
The	O
final	O
additional	O
card	O
(	O
a	O
3278	B-Operating_System
emulator	O
)	O
provides	O
the	O
communication	O
interface	O
to	O
the	O
host	O
mainframe	B-Architecture
.	O
</s>
<s>
3270	B-Operating_System
PC	O
(	O
System	O
Unit	O
5271	O
)	O
-	O
original	O
3270	B-Operating_System
PC	O
,	O
initially	O
offered	O
in	O
three	O
different	O
Models	O
numbered	O
2	O
,	O
4	O
,	O
and	O
6	O
.	O
</s>
<s>
Model	O
6	O
had	O
a	O
retail	O
price	O
of	O
at	O
its	O
launch	O
(	O
with	O
512KB	O
RAM	O
)	O
,	O
not	O
including	O
display	O
,	O
cables	O
and	O
software	O
;	O
a	O
working	O
configuration	O
with	O
an	O
additional	O
192KB	O
RAM	O
,	O
color	O
display	O
(	O
model	O
5272	O
)	O
and	O
the	O
basic	O
cabling	O
and	O
software	O
(	O
but	O
without	O
support	O
for	O
host/mainframe	O
-side	O
graphics	O
)	O
ran	O
to	O
.	O
</s>
<s>
A	O
1985	O
review	O
by	O
PC	O
Magazine	O
found	O
that	O
fast	O
file	O
transfer	O
to	O
and	O
from	O
the	O
mainframe	B-Architecture
was	O
the	O
strong	O
selling	O
point	O
of	O
this	O
unit	O
:	O
file	O
transfers	O
that	O
took	O
hours	O
with	O
an	O
Irma	B-Device
board	I-Device
took	O
only	O
minutes	O
with	O
the	O
boards	O
(	O
and	O
software	O
)	O
that	O
came	O
with	O
the	O
3270	B-Operating_System
PC	O
.	O
</s>
<s>
The	O
3270	B-Operating_System
PC	O
suffered	O
however	O
from	O
incompatibility	O
problems	O
with	O
other	O
XT	O
hardware	O
and	O
DOS	O
software	O
(	O
for	O
example	O
,	O
Microsoft	B-Language
QuickBasic	I-Language
)	O
.	O
</s>
<s>
Its	O
3278	B-Operating_System
mainframe	B-Architecture
board	O
was	O
also	O
considered	O
lackluster	O
,	O
in	O
comparison	O
with	O
an	O
IBM	O
3279	O
graphics	O
terminal	O
,	O
because	O
it	O
provides	O
only	O
a	O
24-line	O
display	O
during	O
mainframe	B-Architecture
sessions	O
,	O
requiring	O
either	O
PC-side	O
scrolling	O
for	O
the	O
32-line	O
applications	O
typically	O
used	O
with	O
a	O
3279	O
,	O
or	O
explicit	O
24-line	O
application	O
support	O
on	O
the	O
mainframe	B-Architecture
side	O
.	O
</s>
<s>
This	O
monochrome	O
display	O
is	O
intended	O
to	O
provide	O
a	O
high-capacity	O
text	O
terminal	O
for	O
simultaneous	O
mainframe	B-Architecture
sessions	O
.	O
</s>
<s>
It	O
has	O
two	O
sets	O
of	O
fonts	O
:	O
one	O
with	O
612-pixel	O
characters	O
,	O
with	O
which	O
it	O
can	O
display	O
text	O
in	O
62	O
rows	O
by	O
160	O
columns	O
,	O
and	O
a	O
larger	O
font	O
with	O
916-pixel	O
characters	O
,	O
with	O
which	O
it	O
can	O
display	O
46	O
rows	O
by	O
106	O
columns	O
of	O
text	O
.	O
</s>
<s>
They	O
(	O
and	O
all	O
subsequent	O
models	O
)	O
also	O
revert	O
to	O
the	O
5151/5272	O
Display	B-Device
Adapter	I-Device
(	O
no	O
Plasma	O
Monitor	O
support	O
)	O
.	O
</s>
<s>
Models	O
31	O
,	O
51	O
,	O
and	O
71	O
revert	O
to	O
256	O
KB	O
RAM	O
on	O
the	O
system	O
board	O
but	O
were	O
also	O
shipped	O
with	O
an	O
Expanded	B-Device
Memory	I-Device
Adapter	I-Device
(	O
XMA	O
)	O
with	O
1	O
MB	O
RAM	O
standard	O
.	O
</s>
<s>
3270	B-Operating_System
PC/G	O
-	O
3270	B-Operating_System
PC	O
with	O
improved	O
graphics	O
hardware	O
and	O
mouse	O
support	O
;	O
it	O
was	O
sold	O
together	O
with	O
an	O
IBM	O
5279	O
Color	O
Display	O
,	O
which	O
is	O
powered	O
by	O
an	O
IBM	O
5278	O
Display	O
Attachment	O
Unit	O
All	O
Points	O
Addressable	O
(	O
APA	O
)	O
graphics	B-Device
card	I-Device
providing	O
720x512	O
resolution	O
and	O
CGA	B-Device
emulation	O
for	O
compatibility	O
.	O
</s>
<s>
initially	O
offered	O
as	O
Model	O
12	O
,	O
14	O
,	O
and	O
16	O
;	O
these	O
have	O
similar	O
disk	O
configuration	O
options	O
(	O
one	O
floppy	O
,	O
two	O
floppies	O
,	O
and	O
one	O
floppy	O
plus	O
on	O
hard	O
disk	O
)	O
as	O
the	O
basic	O
3270	B-Operating_System
PC	O
,	O
but	O
had	O
more	O
standard	O
memory	O
at	O
384	O
KB	O
,	O
512	O
,	O
and	O
respectively	O
576	O
KB	O
.	O
</s>
<s>
3270	B-Operating_System
PC/GX	O
-	O
Extended	O
APA	O
graphics	O
support	O
(	O
10241024	O
)	O
provided	O
by	O
the	O
IBM	O
5378	O
Display	O
Attachment	O
Unit	O
;	O
shipped	O
with	O
a	O
19-inch	O
color	O
or	O
monochrome	O
monitor	O
(	O
IBM	O
5379	O
)	O
.	O
</s>
<s>
The	O
basic	O
3270	B-Operating_System
PC	O
could	O
not	O
be	O
upgraded	O
to	O
the	O
PC/G	O
or	O
PC/GX	O
.	O
</s>
<s>
3270	B-Operating_System
AT	O
(	O
System	O
Unit	O
5273	O
)	O
-	O
corresponds	O
to	O
the	O
3270	B-Operating_System
PC	O
,	O
but	O
based	O
on	O
an	O
IBM	B-Operating_System
AT	I-Operating_System
.	O
</s>
<s>
3270	B-Operating_System
AT/G	O
and	O
GX	O
(	O
System	O
Unit	O
5373	O
)	O
-	O
corresponds	O
to	O
the	O
3270	B-Operating_System
PC/G	O
and	O
PC/GX	O
,	O
respectively	O
,	O
but	O
based	O
on	O
an	O
IBM	B-Operating_System
AT	I-Operating_System
.	O
</s>
<s>
At	O
its	O
launch	O
,	O
the	O
3270	B-Operating_System
PC	O
used	O
the	O
3270	B-Operating_System
PC	O
Control	O
Program	O
as	O
its	O
operating	O
system	O
.	O
</s>
<s>
PC	B-Operating_System
DOS	I-Operating_System
2.0	O
(	O
and	O
later	O
2.1	O
)	O
can	O
run	O
as	O
a	O
task	O
under	O
the	O
Control	O
Program	O
.	O
</s>
<s>
Only	O
one	O
PC	B-Operating_System
DOS	I-Operating_System
task	O
can	O
be	O
run	O
at	O
any	O
given	O
time	O
,	O
but	O
in	O
parallel	O
with	O
this	O
,	O
the	O
Control	O
Program	O
can	O
run	O
up	O
to	O
four	O
mainframe	B-Architecture
sessions	O
.	O
</s>
<s>
The	O
Control	O
Program	O
also	O
provides	O
a	O
basic	O
windowing	O
environment	O
,	O
with	O
up	O
to	O
seven	O
windows	O
;	O
besides	O
the	O
four	O
mainframe	B-Architecture
and	O
one	O
DOS	O
session	O
,	O
it	O
also	O
provides	O
two	O
notepads	O
.	O
</s>
<s>
The	O
notepads	O
can	O
be	O
used	O
to	O
copy	O
text	O
from	O
the	O
PC	B-Operating_System
DOS	I-Operating_System
session	O
to	O
the	O
mainframe	B-Architecture
sessions	O
but	O
not	O
vice	O
versa	O
.	O
</s>
<s>
More	O
useful	O
were	O
the	O
specialized	O
PC	B-Operating_System
DOS	I-Operating_System
file	O
transfer	O
utilities	O
that	O
were	O
available	O
(	O
called	O
simply	O
and	O
)	O
,	O
which	O
allow	O
files	O
to	O
be	O
exchanged	O
with	O
the	O
mainframe	B-Architecture
and	O
provide	O
ASCII/EBCDIC	O
conversion	O
.	O
</s>
<s>
At	O
the	O
launch	O
of	O
the	O
3270	B-Operating_System
PC	O
,	O
the	O
Control	O
Program	O
was	O
the	O
distinguishing	O
software	O
feature	O
between	O
a	O
3270	B-Operating_System
PC	O
and	O
an	O
XT	O
with	O
an	O
added	O
3278	B-Operating_System
board	O
.	O
</s>
<s>
IBM	O
considered	O
the	O
3270	B-Operating_System
PC	O
Control	O
Program	O
to	O
be	O
mainframe	B-Architecture
software	O
,	O
so	O
it	O
did	O
not	O
provide	O
user-installable	O
upgrades	O
.	O
</s>
<s>
The	O
PC/G	O
and	O
PC/GX	O
models	O
run	O
a	O
mainframe-graphics-capable	O
version	O
of	O
the	O
Control	O
Program	O
called	O
the	O
Graphics	O
Control	O
Program	O
(	O
GCP	O
)	O
.	O
</s>
<s>
On	O
the	O
mainframe	B-Architecture
side	O
,	O
the	O
IBM	B-Device
Graphical	I-Device
Data	I-Device
Display	I-Device
Manager	I-Device
(	O
GDDM	B-Device
)	O
release	O
4	O
(	O
and	O
later	O
)	O
is	O
compatible	O
with	O
these	O
two	O
workstations	O
.	O
</s>
<s>
The	O
GDDM	B-Device
provided	O
support	O
for	O
local	O
pan	O
and	O
zoom	O
(	O
without	O
taxing	O
the	O
host	O
mainframe	B-Architecture
)	O
on	O
the	O
PC/G	O
and	O
PC/GX	O
.	O
</s>
<s>
In	O
1987	O
IBM	O
released	O
the	O
IBM	B-Operating_System
3270	I-Operating_System
Workstation	I-Operating_System
Program	I-Operating_System
,	O
which	O
supports	O
both	O
XT	O
and	O
AT	O
models	O
of	O
the	O
3270	B-Operating_System
PCs	B-Device
,	O
as	O
well	O
as	O
the	O
plain	O
XT	O
and	O
AT	O
models	O
(	O
even	O
with	O
an	O
XT	O
or	O
AT	O
keyboard	O
)	O
with	O
a	O
3278	B-Operating_System
board	O
.	O
</s>
<s>
It	O
allows	O
up	O
to	O
six	O
concurrent	O
DOS	O
3.3	O
sessions	O
,	O
but	O
the	O
number	O
of	O
mainframe	B-Architecture
sessions	O
and	O
notepads	O
remained	O
the	O
same	O
(	O
four	O
and	O
two	O
,	O
respectively	O
)	O
.	O
</s>
<s>
BYTE	B-Application
in	O
1984	O
praised	O
the	O
3270	B-Operating_System
PC	O
's	O
3278	B-Operating_System
emulation	O
and	O
color	O
monitor	O
,	O
and	O
concluded	O
that	O
the	O
computer	O
was	O
"	O
a	O
must	O
"	O
for	O
those	O
seeking	O
high-quality	O
graphics	O
or	O
mainframe	B-Architecture
communications	O
.	O
</s>
