<s>
The	O
IBM	B-Device
3705	I-Device
Communications	I-Device
Controller	I-Device
is	O
a	O
simple	O
computer	O
which	O
attaches	O
to	O
an	O
IBM	B-Application
System/360	I-Application
or	O
System/370	B-Device
.	O
</s>
<s>
Its	O
purpose	O
is	O
to	O
connect	O
communication	O
lines	O
to	O
the	O
mainframe	B-Device
channel	I-Device
.	O
</s>
<s>
It	O
was	O
a	O
first	O
communications	B-General_Concept
controller	I-General_Concept
of	O
the	O
popular	O
IBM	B-Device
37xx	I-Device
series	O
.	O
</s>
<s>
Solid	B-Algorithm
Logic	I-Algorithm
Technology	I-Algorithm
components	O
,	O
similar	O
to	O
those	O
in	O
S/370	B-Device
,	O
were	O
used	O
.	O
</s>
<s>
Emulation	O
of	O
the	O
older	O
IBM	B-Device
2703	I-Device
Communications	I-Device
Controller	I-Device
and	O
its	O
predecessors	O
.	O
</s>
<s>
Connection	O
of	O
Systems	B-Architecture
Network	I-Architecture
Architecture	I-Architecture
(	O
SNA	O
)	O
devices	O
to	O
a	O
mainframe	O
.	O
</s>
<s>
This	O
capability	O
derived	O
from	O
the	O
objective	O
of	O
emulating	O
the	O
IBM	B-Device
2703	I-Device
which	O
has	O
a	O
fairly	O
rich	O
control	O
panel	O
.	O
</s>
<s>
Three	O
types	O
of	O
peripherals	O
were	O
available	O
:	O
communications	O
scanners	O
,	O
channel	O
adapters	O
and	O
8	B-Device
"	I-Device
floppy	B-Device
disk	I-Device
(	O
only	O
available	O
in	O
models	O
without	O
a	O
channel	O
adapter	O
)	O
.	O
</s>
<s>
All	O
Amdahl	O
4705s	O
were	O
provided	O
with	O
an	O
8	B-Device
"	I-Device
floppy	B-Device
drive	I-Device
,	O
which	O
was	O
used	O
for	O
diagnostics	O
as	O
well	O
as	O
for	O
remote	O
program	O
loading	O
.	O
</s>
<s>
This	O
floppy	B-Device
drive	I-Device
and	O
all	O
Channel	O
Adapters	O
were	O
contained	O
in	O
the	O
Base	O
Frame	O
,	O
although	O
additional	O
S/370	B-Device
channel	B-Device
I/O	I-Device
interfaces	O
could	O
require	O
an	O
Expansion	O
Frame	O
.	O
</s>
<s>
Six	O
different	O
asynchronous	O
character	O
formats	O
,	O
two	O
forms	O
of	O
Bisync	B-Protocol
and	O
HDLC/SDLC	O
were	O
supported	O
.	O
</s>
<s>
The	O
Type	O
III	O
Communication	O
Scanner	O
was	O
a	O
high	O
performance	O
device	O
for	O
attachment	O
of	O
Bisync	B-Protocol
and	O
HDLC/SDLC	O
lines	O
.	O
</s>
<s>
DMA	B-General_Concept
was	O
used	O
to	O
fetch	O
and	O
store	O
the	O
bytes	O
of	O
a	O
frame	O
.	O
</s>
<s>
IPSANET	B-Protocol
experience	O
was	O
that	O
six	O
full-duplex	O
9.6	O
kbit/s	O
lines	O
carrying	O
a	O
heavy	O
load	O
was	O
the	O
limit	O
.	O
</s>
<s>
Type	O
1	O
and	O
Type	O
4	O
Channel	O
Adapters	O
were	O
designed	O
for	O
270x	B-Device
emulation	O
.	O
</s>
<s>
These	O
adapters	O
could	O
be	O
connected	O
to	O
any	O
of	O
the	O
three	O
System/370	B-Device
channel	O
types	O
but	O
a	O
block	O
multiplexor	O
channel	O
was	O
preferred	O
.	O
</s>
<s>
The	O
IBM	B-Device
3704	I-Device
was	O
an	O
entry	O
level	O
version	O
of	O
the	O
3705	O
.	O
</s>
<s>
DMA	B-General_Concept
devices	O
were	O
not	O
supported	O
on	O
the	O
3704	O
.	O
</s>
<s>
The	O
Amdahl	O
4745	O
was	O
completely	O
and	O
in	O
every	O
respect	O
a	O
logical	O
superset	O
,	O
or	O
a	O
physical	O
subset	O
of	O
the	O
IBM	B-Device
3745	I-Device
.	O
</s>
<s>
Whereas	O
the	O
IBM	B-Device
3745	I-Device
offered	O
one	O
or	O
two	O
physical	O
processors	O
,	O
and	O
one	O
or	O
two	O
physical	O
buses	O
,	O
both	O
apparently	O
for	O
redundancy	O
,	O
the	O
Amdahl	O
offered	O
one	O
very	O
highly	O
reliable	O
physical	O
processor	O
and	O
one	O
very	O
highly	O
reliable	O
physical	O
bus	O
(	O
but	O
two	O
logical	O
buses	O
)	O
,	O
with	O
no	O
apparent	O
need	O
for	O
redundancy	O
.	O
</s>
<s>
Whereas	O
the	O
IBM	B-Device
3745	I-Device
offered	O
two	O
buses	O
,	O
the	O
Amdahl	O
4745	O
offered	O
a	O
single	O
bus	O
which	O
throughput	O
capacity	O
exceeded	O
the	O
aggregate	O
throughput	O
capacity	O
of	O
the	O
two	O
buses	O
of	O
the	O
IBM	B-Device
3745	I-Device
.	O
</s>
<s>
The	O
design	O
of	O
the	O
Amdahl	O
4745	O
was	O
such	O
that	O
the	O
control	O
program	O
(	O
NCP	O
)	O
could	O
not	O
tell	O
whether	O
it	O
was	O
operating	O
in	O
an	O
IBM	B-Device
3745	I-Device
or	O
in	O
an	O
Amdahl	O
4745	O
(	O
or	O
,	O
for	O
that	O
matter	O
,	O
in	O
an	O
IBM	O
3725	O
or	O
in	O
an	O
Amdahl	O
4725	O
)	O
.	O
</s>
<s>
Amdahl	O
's	O
logical	O
and	O
physical	O
simulation	O
of	O
the	O
IBM	B-Device
3745	I-Device
(	O
IBM	O
3725	O
)	O
was	O
that	O
complete	O
.	O
</s>
<s>
Later	O
,	O
a	O
very	O
high-speed	O
scanner	O
was	O
offered	O
with	O
the	O
Amdahl	O
4745	O
(	O
and	O
also	O
with	O
the	O
Amdahl	O
4725	O
,	O
for	O
which	O
IBM	O
had	O
no	O
such	O
corresponding	O
3725	O
offering	O
)	O
which	O
offered	O
increased	O
redundancy	O
over	O
the	O
IBM	B-Device
3745	I-Device
very	O
high-speed	O
scanner	O
(	O
1.544	O
Mbit/s	O
,	O
T1	O
,	O
or	O
2.048	O
Mbit/s	O
,	O
E1	O
)	O
by	O
having	O
the	O
line	O
switchable	O
to	O
a	O
backup	O
4725/4745	O
under	O
operator	O
console	O
control	O
.	O
</s>
<s>
The	O
3705	O
was	O
eventually	O
replaced	O
by	O
the	O
3720	B-Device
and	O
3725	O
.	O
</s>
<s>
The	O
3745	B-Device
was	O
similar	O
but	O
not	O
entirely	O
compatible	O
.	O
</s>
