<s>
The	O
IBM	B-Device
1620	I-Device
was	O
announced	O
by	O
IBM	O
on	O
October	O
21	O
,	O
1959	O
,	O
and	O
marketed	O
as	O
an	O
inexpensive	O
scientific	O
computer	O
.	O
</s>
<s>
Modified	O
versions	O
of	O
the	O
1620	O
were	O
used	O
as	O
the	O
CPU	B-General_Concept
of	O
the	O
IBM	B-Device
1710	I-Device
and	O
IBM	O
1720	O
Industrial	O
Process	O
Control	O
Systems	O
(	O
making	O
it	O
the	O
first	O
digital	O
computer	O
considered	O
reliable	O
enough	O
for	O
real-time	B-General_Concept
process	O
control	O
of	O
factory	O
equipment	O
)	O
.	O
</s>
<s>
Being	O
variable-word-length	O
decimal	O
,	O
as	O
opposed	O
to	O
fixed-word-length	O
pure	O
binary	O
,	O
made	O
it	O
an	O
especially	O
attractive	O
first	O
computer	O
to	O
learn	O
on	O
and	O
hundreds	O
of	O
thousands	O
of	O
students	O
had	O
their	O
first	O
experiences	O
with	O
a	O
computer	O
on	O
the	O
IBM	B-Device
1620	I-Device
.	O
</s>
<s>
Core	B-General_Concept
memory	I-General_Concept
cycle	O
times	O
were	O
20	O
microseconds	O
for	O
the	O
(	O
earlier	O
)	O
Model	O
I	O
,	O
10	O
microseconds	O
for	O
the	O
Model	O
II	O
(	O
about	O
a	O
thousand	O
times	O
slower	O
than	O
typical	O
computer	O
main	O
memory	O
in	O
2006	O
)	O
.	O
</s>
<s>
The	O
IBM	B-Device
1620	I-Device
was	O
a	O
variable	O
"	O
word	O
"	O
length	O
decimal	O
(	O
BCD	O
)	O
computer	O
with	O
a	O
magnetic-core	O
memory	O
that	O
could	O
hold	O
:	O
</s>
<s>
Memory	O
was	O
accessed	O
two	O
decimal	O
digits	O
at	O
the	O
same	O
time	O
(	O
even-odd	O
digit	O
pair	O
for	O
numeric	B-Algorithm
data	O
or	O
one	O
alphameric	O
character	O
for	O
text	O
data	O
)	O
.	O
</s>
<s>
It	O
was	O
set	O
to	O
mark	O
the	O
most	O
significant	O
digit	O
of	O
a	O
number	O
(	O
wordmark	B-Device
)	O
.	O
</s>
<s>
In	O
the	O
middle	O
three	O
digits	O
of	O
five-digit	O
addresses	O
(	O
on	O
the	O
1620	O
II	O
)	O
they	O
were	O
set	O
to	O
select	O
one	O
of	O
seven	O
index	B-General_Concept
registers	I-General_Concept
.	O
</s>
<s>
Instructions	B-General_Concept
were	O
fixed	O
length	O
(	O
12	O
decimal	O
digits	O
)	O
,	O
consisting	O
of	O
a	O
two-digit	O
"	O
op	B-Language
code	I-Language
"	O
,	O
a	O
five-digit	O
"	O
P	O
Address	O
"	O
(	O
usually	O
the	O
destination	O
address	O
)	O
,	O
and	O
a	O
five-digit	O
"	O
Q	O
Address	O
"	O
(	O
usually	O
the	O
source	O
address	O
or	O
the	O
source	O
immediate	O
value	O
)	O
.	O
</s>
<s>
Some	O
instructions	B-General_Concept
,	O
such	O
as	O
the	O
B	O
(	O
branch	O
)	O
instruction	O
,	O
used	O
only	O
the	O
P	O
Address	O
,	O
and	O
later	O
smart	O
assemblers	B-Language
included	O
a	O
"	O
B7	O
"	O
instruction	O
that	O
generated	O
a	O
seven-digit	O
branch	O
instruction	O
(	O
op	B-Language
code	I-Language
,	O
P	O
address	O
,	O
and	O
one	O
extra	O
digit	O
because	O
the	O
next	O
instruction	O
had	O
to	O
start	O
on	O
an	O
even-numbered	O
digit	O
)	O
.	O
</s>
<s>
Floating-point	B-Algorithm
data	O
"	O
words	O
"	O
(	O
using	O
the	O
hardware	O
floating	B-Algorithm
point	I-Algorithm
option	O
)	O
could	O
be	O
any	O
size	O
from	O
4	O
decimal	O
digits	O
up	O
to	O
102	O
decimal	O
digits	O
(	O
2	O
to	O
100	O
digits	O
for	O
the	O
mantissa	B-Algorithm
and	O
two	O
digits	O
for	O
the	O
exponent	O
)	O
.	O
</s>
<s>
The	O
Fortran	B-Application
II	O
compiler	O
offered	O
limited	O
access	O
to	O
this	O
flexibility	O
via	O
a	O
"	O
Source	O
Program	O
Control	O
Card	O
"	O
preceding	O
the	O
fortran	B-Application
source	O
in	O
a	O
fixed	O
format	O
:	O
</s>
<s>
The	O
*	O
in	O
column	O
one	O
,	O
ff	O
the	O
number	O
of	O
digits	O
for	O
the	O
mantissa	B-Algorithm
of	O
floating-point	B-Algorithm
numbers	I-Algorithm
(	O
allowing	O
02	O
to	O
28	O
)	O
,	O
kk	O
the	O
number	O
of	O
digits	O
for	O
fixed-point	O
numbers	O
(	O
allowing	O
04	O
to	O
10	O
)	O
and	O
s	O
is	O
to	O
specify	O
the	O
memory	O
size	O
of	O
the	O
computer	O
to	O
run	O
the	O
code	O
if	O
not	O
the	O
current	O
computer	O
:	O
2	O
,	O
4	O
,	O
or	O
6	O
for	O
memories	O
of	O
20,000	O
or	O
40,000	O
or	O
60,000	O
digits	O
.	O
</s>
<s>
The	O
machine	O
had	O
no	O
programmer-accessible	O
registers	O
:	O
all	O
operations	O
were	O
memory	O
to	O
memory	O
(	O
including	O
the	O
index	B-General_Concept
registers	I-General_Concept
of	O
the	O
1620	O
II	O
)	O
.	O
</s>
<s>
The	O
table	O
below	O
lists	O
Alphameric	O
mode	O
characters	O
(	O
and	O
op	B-Language
codes	I-Language
)	O
.	O
</s>
<s>
invalid	O
Ж	O
❚	O
21	O
TRNM	O
Transmit	O
Record	O
No	O
RM	O
(	O
Model	O
II	O
)	O
invalid	O
Ж	O
❚	O
21	O
1	O
TR	O
Transmit	O
Record	O
invalid	O
Ж	O
❚	O
21	O
2	O
SF	O
Set	O
Flag	O
=	O
=	O
=	O
=	O
8	O
21	O
8	O
21	O
3-81-2-8	O
3-8	O
21	O
21	O
CF	O
Clear	O
Flag	O
@	O
@	O
@	O
@	O
C84	O
C84	O
4-8	O
4-8	O
21	O
4	O
K	O
Control	O
(	O
I/O	O
device	O
)	O
invalid	O
Ж	O
❚	O
21	O
4	O
1	O
DN	O
Dump	O
Numeric	B-Algorithm
invalid	O
Ж	O
❚	O
21	O
42	O
RN	O
Read	O
Numeric	B-Algorithm
invalid	O
Ж	O
❚	O
21	O
421	O
RA	O
Read	O
Alphameric	O
invalid	O
Ж	O
❚	O
21	O
8	O
WN	O
Write	O
Numeric	B-Algorithm
invalid	O
Ж	O
❚	O
21	O
81	O
WA	O
Write	O
Alphameric	O
A	O
A	O
A	O
A	O
X01	O
X01	O
12-1	O
12-1	O
4	O
1	O
NOP	O
No	O
Operation	O
B	O
B	O
B	O
B	O
X02	O
X02	O
12-2	O
12-2	O
4	O
2	O
BB	O
Branch	O
Back	O
C	O
C	O
C	O
C	O
X0C21	O
X0C21	O
12-312-1-2	O
12-3	O
4	O
21	O
BD	O
Branch	O
On	O
Digit	O
D	O
D	O
D	O
D	O
X04	O
X04	O
12-4	O
12-4	O
4	O
4	O
BNF	O
Branch	O
No	O
Flag	O
E	O
E	O
E	O
E	O
X0C	O
4	O
1	O
X0C	O
4	O
1	O
12-512-1-4	O
12-5	O
4	O
4	O
1	O
BNR	O
Branch	O
No	O
Record	O
Mark	O
F	O
F	O
F	O
F	O
X0C	O
42	O
X0C	O
42	O
12-612-2-4	O
12-6	O
4	O
42	O
BI	O
Branch	O
Indicator	O
UMK	O
UnmaskMK	O
Mask	O
1710	O
interrupt	O
feature	O
.	O
</s>
<s>
R-9	O
R	O
R	O
R	O
X81	O
X81	O
11-911-1-8	O
11-9	O
4	O
1	O
81	O
invalid	O
Ж	O
❚	O
42	O
BS	O
Branch	O
and	O
Select	O
(	O
Model	O
II	O
)	O
invalid	O
Ж	O
❚	O
42	O
1	O
BX	O
Branch	O
and	O
Modify	O
Index	B-General_Concept
Register	I-General_Concept
Optional	O
special	O
feature	O
(	O
Model	O
II	O
)	O
.	O
</s>
<s>
S	O
S	O
S	O
S	O
0C2	O
0C2	O
0-2	O
0-2	O
42	O
2	O
BXM	O
Branch	O
and	O
Modify	O
Index	B-General_Concept
Register	I-General_Concept
Immediate	O
Optional	O
special	O
feature	O
(	O
Model	O
II	O
)	O
.	O
</s>
<s>
T	O
T	O
T	O
T	O
021	O
021	O
0-30-1-2	O
0-3	O
42	O
21	O
BCX	O
Branch	O
Conditionally	O
and	O
Modify	O
Index	B-General_Concept
Register	I-General_Concept
Optional	O
special	O
feature	O
(	O
Model	O
II	O
)	O
.	O
</s>
<s>
U	O
U	O
U	O
U	O
0C	O
4	O
0C	O
4	O
0-4	O
0-4	O
42	O
4	O
BCXM	O
Branch	O
Conditionally	O
and	O
Modify	O
Index	B-General_Concept
Register	I-General_Concept
Immediate	O
Optional	O
special	O
feature	O
(	O
Model	O
II	O
)	O
.	O
</s>
<s>
V	O
V	O
V	O
V	O
04	O
1	O
04	O
1	O
0-50-1-4	O
0-5	O
42	O
4	O
1	O
BLX	O
Branch	O
and	O
Load	O
Index	B-General_Concept
Register	I-General_Concept
Optional	O
special	O
feature	O
(	O
Model	O
II	O
)	O
.	O
</s>
<s>
W	O
W	O
W	O
W	O
042	O
042	O
0-60-2-4	O
0-6	O
42	O
42	O
BLXM	O
Branch	O
and	O
Load	O
Index	B-General_Concept
Register	I-General_Concept
Immediate	O
Optional	O
special	O
feature	O
(	O
Model	O
II	O
)	O
.	O
</s>
<s>
X	O
X	O
X	O
X	O
0C	O
421	O
0C	O
421	O
0-70-1-2-4	O
0-7	O
42	O
421	O
BSX	O
Branch	O
and	O
Store	O
Index	B-General_Concept
Register	I-General_Concept
Optional	O
special	O
feature	O
(	O
Model	O
II	O
)	O
.	O
</s>
<s>
2	O
2	O
2	O
2	O
2	O
2	O
2	O
2	O
421	O
2	O
TNS	O
Transmit	O
Numeric	B-Algorithm
Strip	O
Optional	O
special	O
feature	O
(	O
Model	O
I	O
)	O
.Standard	O
(	O
Model	O
II	O
)	O
.	O
</s>
<s>
3	O
3	O
3	O
3	O
C21	O
C21	O
3	O
3	O
421	O
21	O
TNF	O
Transmit	O
Numeric	B-Algorithm
Fill	O
Optional	O
special	O
feature	O
(	O
Model	O
I	O
)	O
.Standard	O
(	O
Model	O
II	O
)	O
.	O
</s>
<s>
Modifiers	O
in	O
Q	O
field	O
invalid	O
Ж	O
❚	O
8	O
42	O
SLTA	O
Select	O
TASSLAR	O
Select	O
ADC	O
RegisterSLTC	O
Select	O
Real-Time	B-General_Concept
ClockSLIC	O
Select	O
Input	O
ChannelSLCB	O
Select	O
Contact	O
BlockSLME	O
Select	O
Manual	O
Entry	O
1710	O
feature	O
.	O
</s>
<s>
Modifiers	O
in	O
Q	O
field	O
invalid	O
Ж	O
❚	O
8	O
F	O
42	O
RNIC	O
Read	O
Numeric	B-Algorithm
Input	O
Channel	O
1710	O
feature	O
.	O
</s>
<s>
Modifiers	O
in	O
Q	O
field	O
invalid	O
Ж	O
❚	O
8	O
8	O
WNOC	O
Write	O
Numeric	B-Algorithm
Output	O
Channel	O
1710	O
feature	O
.	O
</s>
<s>
The	O
table	O
below	O
lists	O
numeric	B-Algorithm
mode	O
characters	O
.	O
</s>
<s>
Although	O
the	O
IBM	B-Device
1620	I-Device
's	O
architecture	O
was	O
very	O
popular	O
in	O
the	O
scientific	O
and	O
engineering	O
community	O
,	O
computer	O
scientist	O
Edsger	O
Dijkstra	O
pointed	O
out	O
several	O
flaws	O
in	O
its	O
design	O
in	O
EWD37	O
,	O
"	O
A	O
review	O
of	O
the	O
IBM	B-Device
1620	I-Device
data	O
processing	O
system	O
"	O
.	O
</s>
<s>
The	O
successor	O
to	O
the	O
1620	O
,	O
the	O
IBM	B-Device
1130	I-Device
,	O
was	O
based	O
on	O
a	O
totally	O
different	O
,	O
16-bit	O
binary	O
architecture	O
.	O
</s>
<s>
(	O
The	O
1130	O
line	O
retained	O
one	O
1620	O
peripheral	O
,	O
the	O
IBM	B-Device
1627	I-Device
drum	O
plotter	O
.	O
)	O
</s>
<s>
Monitor	O
I	O
and	O
Monitor	O
II	O
disk	O
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
Both	O
Monitor	O
systems	O
required	O
20,000	O
digits	O
or	O
more	O
of	O
memory	O
and	O
one	O
or	O
more	O
1311	B-Device
disk	O
drives	O
.	O
</s>
<s>
The	O
IBM	B-Device
1620	I-Device
Model	O
I	O
(	O
commonly	O
called	O
"	O
1620	O
"	O
from	O
1959	O
until	O
the	O
1962	O
introduction	O
of	O
the	O
Model	O
II	O
)	O
was	O
the	O
original	O
.	O
</s>
<s>
It	O
lacked	O
conventional	O
ALU	B-General_Concept
hardware	O
:	O
arithmetic	O
was	O
done	O
by	O
memory	B-General_Concept
table	I-General_Concept
lookup	O
.	O
</s>
<s>
Floating	B-Algorithm
point	I-Algorithm
arithmetic	I-Algorithm
instructions	B-General_Concept
were	O
an	O
available	O
option	O
(	O
if	O
the	O
divide	O
option	O
was	O
installed	O
)	O
.	O
</s>
<s>
The	O
first	O
20,000	O
decimal	O
digits	O
of	O
magnetic-core	O
memory	O
were	O
internal	O
to	O
the	O
CPU	B-General_Concept
itself	O
(	O
which	O
reduced	O
the	O
floor	O
space	O
requirements	O
of	O
the	O
basic	O
system	O
)	O
.	O
</s>
<s>
A	O
Memory	O
Address	O
Register	O
Storage	O
(	O
MARS	O
)	O
Core	B-General_Concept
memory	I-General_Concept
read	O
,	O
clear	O
,	O
or	O
write	O
operation	O
took	O
2μs	O
and	O
each	O
write	O
operation	O
was	O
automatically	O
(	O
but	O
not	O
necessarily	O
immediately	O
)	O
preceded	O
by	O
a	O
read	O
or	O
clear	O
operation	O
of	O
the	O
same	O
"	O
register(s )	O
"	O
during	O
the	O
20μs	O
memory	O
cycle	O
.	O
</s>
<s>
The	O
central	O
processor	O
clock	O
speed	O
was	O
1MHz	O
,	O
which	O
was	O
divided	O
by	O
20	O
by	O
a	O
10-position	O
ring	B-General_Concept
counter	I-General_Concept
to	O
provide	O
the	O
system	O
timing	O
and	O
control	O
signals	O
.	O
</s>
<s>
Instructions	B-General_Concept
took	O
eight	O
memory	O
cycles	O
(	O
160μs	O
)	O
to	O
fetch	O
and	O
a	O
variable	O
number	O
of	O
memory	O
cycles	O
to	O
execute	O
.	O
</s>
<s>
The	O
IBM	B-Device
1620	I-Device
Model	O
II	O
(	O
commonly	O
called	O
simply	O
the	O
Model	O
II	O
)	O
was	O
a	O
vastly	O
improved	O
implementation	O
,	O
compared	O
to	O
the	O
original	O
Model	O
I	O
.	O
</s>
<s>
It	O
had	O
basic	O
ALU	B-General_Concept
hardware	O
for	O
addition	O
and	O
subtraction	O
,	O
but	O
multiplication	O
was	O
still	O
done	O
by	O
in-core	B-General_Concept
memory	I-General_Concept
table	O
lookup	O
,	O
using	O
a	O
200-digit	O
table	O
(	O
at	O
address	O
00100	O
..	O
00299	O
)	O
.	O
</s>
<s>
Memory	B-General_Concept
addresses	I-General_Concept
at	O
address	O
00300	O
..	O
00399	O
were	O
freed	O
by	O
the	O
replacement	O
of	O
the	O
addition	O
table	O
with	O
hardware	O
,	O
resulting	O
in	O
storage	O
of	O
two	O
selectable	O
"	O
bands	O
"	O
of	O
seven	O
five-digit	O
index	B-General_Concept
registers	I-General_Concept
.	O
</s>
<s>
Floating	B-Algorithm
point	I-Algorithm
arithmetic	I-Algorithm
was	O
an	O
available	O
option	O
,	O
as	O
were	O
octal	O
input/output	O
,	O
logical	O
operations	O
,	O
and	O
base	O
conversion	O
to/from	O
decimal	O
instructions	B-General_Concept
.	O
</s>
<s>
The	O
entire	O
core	B-General_Concept
memory	I-General_Concept
was	O
in	O
the	O
IBM	O
1625	O
memory	O
unit	O
.	O
</s>
<s>
A	O
Memory	O
Address	O
Register	O
Storage	O
(	O
MARS	O
)	O
core	B-General_Concept
memory	I-General_Concept
read	O
,	O
clear	O
,	O
or	O
write	O
operation	O
took	O
1.5µs	O
and	O
each	O
write	O
operation	O
was	O
automatically	O
(	O
but	O
not	O
necessarily	O
immediately	O
)	O
preceded	O
by	O
a	O
read	O
or	O
clear	O
operation	O
of	O
the	O
same	O
"	O
register(s )	O
"	O
during	O
the	O
10µs	O
memory	O
cycle	O
.	O
</s>
<s>
The	O
processor	O
clock	O
speed	O
was	O
also	O
doubled	O
,	O
to	O
2MHz	O
,	O
which	O
was	O
still	O
divided	O
by	O
20	O
by	O
a	O
10	O
position	O
ring	B-General_Concept
counter	I-General_Concept
to	O
provide	O
the	O
system	O
timing/control	O
signals	O
.	O
</s>
<s>
Instructions	B-General_Concept
took	O
either	O
1	O
,	O
4	O
,	O
or	O
6	O
memory	O
cycles	O
(	O
10µs	O
,	O
40µs	O
,	O
or	O
60µs	O
)	O
to	O
fetch	O
and	O
a	O
variable	O
number	O
of	O
memory	O
cycles	O
to	O
execute	O
.	O
</s>
<s>
While	O
the	O
Lower	O
console	B-Device
for	O
both	O
the	O
Model	O
1	O
and	O
the	O
Model	O
2	O
IBM	B-Device
1620	I-Device
systems	O
had	O
the	O
same	O
lamps	O
and	O
switches	O
,	O
the	O
Upper	O
console	B-Device
of	O
the	O
pair	O
were	O
partly	O
different	O
.	O
</s>
<s>
The	O
balance	O
of	O
the	O
Upper	O
console	B-Device
was	O
the	O
same	O
on	O
both	O
models	O
:	O
</s>
<s>
The	O
Model	O
I	O
console	B-Device
typewriter	O
was	O
a	O
modified	O
Model	O
B1	O
,	O
interfaced	O
by	O
a	O
set	O
of	O
relays	O
,	O
and	O
it	O
typed	O
at	O
only	O
10	O
characters	O
per	O
second	O
.	O
</s>
<s>
There	O
were	O
a	O
set	O
of	O
instructions	B-General_Concept
that	O
wrote	O
to	O
the	O
typewriter	O
,	O
or	O
read	O
from	O
it	O
.	O
</s>
<s>
The	O
general	O
RN	O
(	O
read	O
numeric	B-Algorithm
)	O
and	O
WN	O
(	O
write	O
numeric	B-Algorithm
)	O
instructions	B-General_Concept
had	O
assembly	B-Language
language	I-Language
mnemonics	O
that	O
supplied	O
the	O
"	O
device	O
"	O
code	O
in	O
the	O
second	O
address	O
field	O
,	O
and	O
the	O
control	O
code	O
in	O
the	O
low-order	O
digit	O
of	O
the	O
second	O
address	O
field	O
.	O
</s>
<s>
WNTY	O
:	O
Write	O
Numeric	B-Algorithm
TYpewriter	O
:	O
each	O
memory	O
location	O
contained	O
a	O
6-bit	O
character	O
in	O
the	O
range	O
of	O
000000	O
to	O
001001	O
;	O
with	O
this	O
instruction	O
,	O
each	O
memory	O
location	O
was	O
rendered	O
as	O
one	O
of	O
the	O
characters	O
"	O
0	O
"	O
through	O
"	O
9	O
"	O
.	O
</s>
<s>
To	O
simplify	O
input	O
and	O
output	O
,	O
there	O
were	O
two	O
instructions	B-General_Concept
:	O
</s>
<s>
IBM	B-Device
1311	I-Device
Disk	O
drive	O
:	O
Model	O
3	O
master	O
drive	O
controlling	O
up	O
to	O
3Model	O
2	O
slave	O
drives	O
.	O
</s>
<s>
A	O
faster	O
output	O
option	O
,	O
the	O
IBM	B-Device
1443	I-Device
printer	I-Device
was	O
introduced	O
May	O
6	O
,	O
1963	O
,	O
and	O
its	O
150	O
–	O
600	O
lines/minute	O
capability	O
was	O
available	O
for	O
use	O
with	O
either	O
model	O
of	O
the	O
1620	O
.	O
</s>
<s>
The	O
"	O
operating	B-General_Concept
system	I-General_Concept
"	O
for	O
the	O
computer	O
constituted	O
the	O
human	O
operator	O
,	O
who	O
would	O
use	O
controls	O
on	O
the	O
computer	O
console	B-Device
,	O
which	O
consisted	O
of	O
a	O
front	B-Device
panel	I-Device
and	O
typewriter	O
,	O
to	O
load	O
programs	O
from	O
the	O
available	O
bulk	O
storage	O
media	O
such	O
as	O
decks	O
of	O
punched	O
cards	O
or	O
rolls	O
of	O
paper	O
tape	O
that	O
were	O
kept	O
in	O
cabinets	O
nearby	O
.	O
</s>
<s>
Later	O
,	O
the	O
model	O
1311	B-Device
disc	O
storage	O
device	O
attached	O
to	O
the	O
computer	O
enabled	O
a	O
reduction	O
in	O
the	O
fetch	O
and	O
carry	O
of	O
card	O
decks	O
or	O
paper	O
tape	O
rolls	O
,	O
and	O
a	O
simple	O
"	O
Monitor	O
"	O
operating	B-General_Concept
system	I-General_Concept
could	O
be	O
loaded	O
to	O
help	O
in	O
selecting	O
what	O
to	O
load	O
from	O
disc	O
.	O
</s>
<s>
This	O
was	O
effected	O
by	O
using	O
the	O
console	B-Device
facilities	O
to	O
load	O
a	O
simple	O
computer	O
program	O
via	O
typing	O
its	O
machine	O
code	O
at	O
the	O
console	B-Device
typewriter	O
,	O
running	O
it	O
,	O
and	O
stopping	O
it	O
.	O
</s>
<s>
This	O
meant	O
transmit	O
field	O
immediate	O
(	O
the	O
16	O
:	O
two-digit	O
op-codes	B-Language
)	O
to	O
address	O
00010	O
the	O
immediate	O
constant	O
field	O
having	O
the	O
value	O
00000	O
(	O
five-digit	O
operand	O
fields	O
,	O
the	O
second	O
being	O
from	O
address	O
11	O
back	O
to	O
7	O
)	O
,	O
decrementing	O
source	O
and	O
destination	O
addresses	O
until	O
such	O
time	O
as	O
a	O
digit	O
with	O
a	O
"	O
flag	O
"	O
was	O
copied	O
.	O
</s>
<s>
Instead	O
there	O
was	O
a	O
button	O
on	O
the	O
console	B-Device
called	O
Modify	O
which	O
when	O
pressed	O
together	O
with	O
the	O
Check	O
Reset	O
button	O
,	O
when	O
the	O
computer	O
was	O
in	O
Manual	O
mode	O
,	O
would	O
set	O
the	O
computer	O
in	O
a	O
mode	O
that	O
would	O
clear	O
all	O
of	O
memory	O
in	O
a	O
tenth	O
of	O
one	O
second	O
regardless	O
of	O
how	O
much	O
memory	O
you	O
had	O
;	O
when	O
you	O
pressed	O
Start	O
.	O
</s>
<s>
Other	O
than	O
typing	O
machine	O
code	O
at	O
the	O
console	B-Device
,	O
a	O
program	O
could	O
be	O
loaded	O
via	O
either	O
the	O
paper	O
tape	O
reader	O
,	O
the	O
card	O
reader	O
,	O
or	O
any	O
disk	O
drive	O
.	O
</s>
<s>
Loading	O
from	O
either	O
tape	O
or	O
disk	O
required	O
first	O
typing	O
a	O
"	O
bootstrap	O
"	O
routine	O
on	O
the	O
console	B-Device
typewriter	O
.	O
</s>
<s>
And	O
the	O
console	B-Device
typewriter	O
allowed	O
entering	O
data	O
and	O
getting	O
output	O
in	O
an	O
interactive	O
fashion	O
,	O
instead	O
of	O
just	O
getting	O
the	O
normal	O
printed	O
output	O
from	O
a	O
blind	O
batch	O
run	O
on	O
a	O
pre-packaged	O
data	O
set	O
.	O
</s>
<s>
As	O
well	O
,	O
there	O
were	O
four	O
program	B-Device
switches	I-Device
on	O
the	O
console	B-Device
whose	O
state	O
a	O
running	O
program	O
could	O
test	O
and	O
so	O
have	O
its	O
behavior	O
directed	O
by	O
its	O
user	O
.	O
</s>
<s>
The	O
computer	O
operator	O
could	O
also	O
stop	O
a	O
running	O
program	O
(	O
or	O
it	O
may	O
come	O
to	O
a	O
deliberately	O
programmed	O
stop	O
)	O
then	O
investigate	O
or	O
modify	O
the	O
contents	O
of	O
memory	O
:	O
being	O
decimal-based	O
,	O
this	O
was	O
quite	O
easy	O
;	O
even	O
floating-point	B-Algorithm
numbers	I-Algorithm
could	O
be	O
read	O
at	O
a	O
glance	O
.	O
</s>
<s>
The	O
most	O
important	O
items	O
on	O
the	O
1620	O
's	O
console	B-Device
were	O
a	O
pair	O
of	O
buttons	O
labeled	O
Insert	O
&	O
Release	O
,	O
and	O
the	O
console	B-Device
typewriter	O
.	O
</s>
<s>
Insert	O
–	O
Pressing	O
this	O
key	O
with	O
the	O
computer	O
in	O
Manual	O
mode	O
reset	O
the	O
program	O
counter	O
(	O
in	O
the	O
MARS	O
core	B-General_Concept
memory	I-General_Concept
)	O
to	O
zero	O
,	O
switched	O
the	O
computer	O
into	O
Automatic	O
and	O
Insert	O
modes	O
,	O
and	O
simulated	O
the	O
execution	O
of	O
a	O
Read	O
Numeric	B-Algorithm
from	O
Typewriter	O
to	O
address	O
zero	O
(	O
unlocked	O
the	O
typewriter	O
keyboard	O
,	O
shifted	O
the	O
typewriter	O
into	O
numeric	B-Algorithm
mode	O
)	O
.	O
</s>
<s>
Note	O
:	O
unlike	O
a	O
real	O
Read	O
Numeric	B-Algorithm
from	O
Typewriter	O
,	O
Insert	O
mode	O
would	O
force	O
a	O
Release	O
after	O
100	O
digits	O
had	O
been	O
typed	O
to	O
prevent	O
overwriting	O
the	O
arithmetic	O
tables	O
.	O
</s>
<s>
The	O
typewriter	O
is	O
used	O
for	O
operator	O
input/output	O
,	O
both	O
as	O
the	O
main	O
console	B-Device
control	O
of	O
the	O
computer	O
and	O
for	O
program	O
controlled	O
input/output	O
.	O
</s>
<s>
Later	O
models	O
of	O
the	O
typewriter	O
had	O
a	O
special	O
key	O
marked	O
R-S	O
that	O
combined	O
the	O
functions	O
of	O
the	O
console	B-Device
Release	O
&	O
Start	O
buttons	O
(	O
this	O
would	O
be	O
considered	O
equivalent	O
to	O
an	O
Enter	O
key	O
on	O
a	O
modern	O
keyboard	O
)	O
.	O
</s>
<s>
Note	O
:	O
several	O
keys	O
on	O
the	O
typewriter	O
did	O
not	O
generate	O
input	O
characters	O
,	O
these	O
included	O
Tab	O
and	O
Return	O
(	O
the	O
1620s	O
alphameric	O
and	O
numeric	B-Algorithm
BCD	O
character	O
sets	O
lacked	O
character	O
codes	O
for	O
these	O
keys	O
)	O
.	O
</s>
<s>
The	O
next	O
most	O
important	O
items	O
on	O
the	O
console	B-Device
were	O
the	O
buttons	O
labeled	O
Start	O
,	O
Stop-SIE	O
,	O
and	O
Instant	O
Stop-SCE	O
.	O
</s>
<s>
Save	O
–	O
Pressing	O
this	O
key	O
with	O
the	O
computer	O
in	O
Manual	O
mode	O
saved	O
the	O
program	O
counter	O
into	O
another	O
register	O
in	O
the	O
MARS	O
core	B-General_Concept
memory	I-General_Concept
and	O
activated	O
Save	O
mode	O
.	O
</s>
<s>
This	O
was	O
used	O
during	O
debugging	O
to	O
remember	O
where	O
the	O
program	O
had	O
been	O
stopped	O
to	O
allow	O
it	O
to	O
be	O
resumed	O
after	O
the	O
debugging	O
instructions	B-General_Concept
that	O
the	O
operator	O
had	O
typed	O
on	O
the	O
typewriter	O
had	O
finished	O
.	O
</s>
<s>
Display	O
MAR	O
–	O
Pressing	O
this	O
key	O
with	O
the	O
computer	O
in	O
Manual	O
mode	O
displayed	O
the	O
selected	O
MARS	O
register	O
and	O
the	O
contents	O
of	O
the	O
memory	O
at	O
that	O
address	O
on	O
the	O
console	B-Device
lamps	O
.	O
</s>
<s>
"	O
Breakpoint	O
"	O
procedureNotesPress	O
Stop-SIEStop	O
the	O
computer	O
at	O
the	O
end	O
of	O
the	O
current	O
instruction.Press	O
SaveSave	O
the	O
address	O
to	O
resume	O
execution	O
at.Press	O
InsertUnlocks	O
typewriter	O
keyboard	O
and	O
shifts	O
into	O
numeric	B-Algorithm
mode.Type	O
35xxxxx0010036xxxxx0010042	O
xxxxx	O
is	O
the	O
address	O
that	O
you	O
plan	O
to	O
set	O
the	O
breakpoint	O
at.Press	O
ReleaseLocks	O
typewriter	O
keyboard.Press	O
StartBegin	O
execution	O
.	O
</s>
<s>
Allow	O
the	O
12	O
digit	O
instruction	O
to	O
print	O
out.Press	O
ReleaseStops	O
the	O
Dump	O
Numeric.Press	O
StartBegin	O
execution.Type	O
48Replace	O
the	O
opcode	B-Language
of	O
the	O
instruction	O
to	O
"	O
break	O
"	O
at	O
with	O
a	O
Halt	O
opcode.Press	O
ReleaseLocks	O
typewriter	O
keyboard.Press	O
StartResume	O
execution	O
.	O
</s>
<s>
Wait	O
until	O
the	O
computer	O
halts	O
at	O
the	O
"	O
breakpoint	O
"	O
.Press	O
InsertUnlocks	O
typewriter	O
keyboard	O
and	O
shifts	O
into	O
numeric	B-Algorithm
mode.Type	O
36xxxxx0010049xxxxx	O
xxxxx	O
is	O
the	O
address	O
that	O
you	O
previously	O
set	O
the	O
breakpoint	O
at	O
,	O
you	O
are	O
now	O
going	O
to	O
clear	O
it.Press	O
ReleaseLocks	O
typewriter	O
keyboard.Press	O
StartBegin	O
execution.Type	O
oooo	O
is	O
the	O
2	O
digit	O
opcode	B-Language
the	O
original	O
12	O
digit	O
instruction	O
previously	O
printed	O
out.Press	O
ReleaseLocks	O
typewriter	O
keyboard.Press	O
Stop-SIEThe	O
machine	O
is	O
now	O
ready	O
to	O
resume	O
execution	O
from	O
the	O
location	O
of	O
the	O
(	O
now	O
cleared	O
)	O
"	O
breakpoint	O
"	O
.	O
</s>
<s>
All	O
of	O
main	O
memory	O
could	O
be	O
cleared	O
from	O
the	O
console	B-Device
by	O
entering	O
and	O
executing	O
a	O
transfer	O
instruction	O
from	O
address	O
to	O
address	O
+1	O
,	O
this	O
would	O
overwrite	O
any	O
word	B-Device
mark	I-Device
,	O
that	O
would	O
normally	O
stop	O
a	O
transfer	O
instruction	O
,	O
and	O
wrap	O
around	O
at	O
the	O
end	O
of	O
memory	O
.	O
</s>
<s>
Power	O
switch	O
–	O
If	O
"	O
on	O
"	O
the	O
unit	O
reader	O
is	O
powered	O
up	O
when	O
the	O
CPU	B-General_Concept
is	O
powered	O
on	O
.	O
</s>
<s>
Bootstrap	O
procedureNotesPress	O
InsertUnlocks	O
typewriter	O
keyboard	O
and	O
shifts	O
into	O
numeric	B-Algorithm
mode.Type	O
36xxxxx0030049yyyyy	O
xxxxx	O
is	O
the	O
address	O
to	O
load	O
the	O
tape	O
into.yyyyy	O
is	O
the	O
address	O
to	O
begin	O
execution.Press	O
ReleaseLocks	O
typewriter	O
keyboard.Press	O
StartBegin	O
execution	O
.	O
</s>
<s>
The	O
IBM	B-Device
1622	I-Device
Card	I-Device
reader/punch	I-Device
could	O
:	O
</s>
<s>
Load	O
–	O
Pressing	O
this	O
key	O
with	O
the	O
reader	O
idle	O
and	O
on	O
and	O
the	O
computer	O
in	O
Manual	O
mode	O
started	O
the	O
reader	O
,	O
reset	O
the	O
program	O
counter	O
(	O
in	O
the	O
MARS	O
core	B-General_Concept
memory	I-General_Concept
)	O
to	O
zero	O
,	O
read	O
one	O
card	O
into	O
the	O
reader	O
's	O
buffer	O
and	O
checked	O
the	O
card	O
for	O
errors	O
,	O
and	O
simulated	O
the	O
execution	O
of	O
a	O
Read	O
Numeric	B-Algorithm
from	O
Card	O
Reader	O
to	O
address	O
zero	O
(	O
reading	O
the	O
80	O
characters	O
of	O
the	O
reader	O
's	O
buffer	O
into	O
memory	B-General_Concept
addresses	I-General_Concept
00000	O
to	O
00079	O
)	O
,	O
then	O
switched	O
the	O
computer	O
into	O
Automatic	O
mode	O
(	O
starting	O
execution	O
at	O
the	O
address	O
in	O
the	O
program	O
counter	O
)	O
.	O
</s>
<s>
The	O
1311	B-Device
Disk	O
drive	O
controls	O
.	O
</s>
<s>
Bootstrap	O
procedureNotesPress	O
InsertUnlocks	O
typewriter	O
keyboard	O
and	O
shifts	O
into	O
numeric	B-Algorithm
mode.Type	O
3400032007013600032007024902402xy1963611300102x	O
Specifies	O
source	O
of	O
Monitor	O
control	O
cards	O
:	O
1	O
=	O
typewriter	O
,	O
3	O
=	O
paper	O
tape	O
,	O
5	O
=	O
cardsy	O
Specifies	O
disk	O
drive	O
on	O
which	O
Monitor	O
resides	O
:	O
1	O
,	O
3	O
,	O
5	O
,	O
702402	O
is	O
the	O
address	O
of	O
the	O
entry	O
point	O
of	O
the	O
Monitor	O
program.Press	O
ReleaseLocks	O
typewriter	O
keyboard.Press	O
StartBegin	O
execution	O
.	O
</s>
<s>
Restart	O
procedureNotesPress	O
InsertUnlocks	O
typewriter	O
keyboard	O
and	O
shifts	O
into	O
numeric	B-Algorithm
mode.Type	O
490225FLG6	O
02256̅	O
is	O
the	O
address	O
of	O
the	O
location	O
containing	O
the	O
address	O
of	O
the	O
restart	O
point	O
of	O
the	O
Monitor	O
program.Note	O
:	O
this	O
procedure	O
assumes	O
the	O
Monitor	O
is	O
already	O
loaded	O
in	O
memoryPress	O
ReleaseLocks	O
typewriter	O
keyboard.Press	O
StartBegin	O
execution	O
.	O
</s>
<s>
The	O
FORTRAN	B-Application
II	O
compiler	O
and	O
SPS	O
assembler	B-Language
were	O
somewhat	O
cumbersome	O
to	O
use	O
by	O
modern	O
standards	O
,	O
however	O
,	O
with	O
repetition	O
,	O
the	O
procedure	O
soon	O
became	O
automatic	O
and	O
you	O
no	O
longer	O
thought	O
about	O
the	O
details	O
involved	O
.	O
</s>
<s>
FORTRAN	B-Application
II	O
compilation	O
procedureNotesSet	O
the	O
Program	B-Device
Switches	I-Device
as	O
follows	O
:	O
</s>
<s>
OFF	O
(	O
Only	O
used	O
if	O
3	O
is	O
ON	O
)	O
Pass	O
I	O
optionsSet	O
Overflow	O
Check	O
switch	O
to	O
Program	O
and	O
all	O
others	O
to	O
StopPress	O
ResetLoad	O
blank	O
cards	O
(	O
face	O
down	O
12-edge	O
first	O
)	O
into	O
the	O
Punch	O
hopper	O
then	O
press	O
Punch	O
StartLoad	O
Pass	O
I	O
of	O
the	O
compiler	O
(	O
face	O
down	O
9-edge	O
first	O
)	O
into	O
the	O
Read	O
hopper	O
then	O
press	O
LoadWait	O
for	O
Pass	O
I	O
to	O
load	O
and	O
print	O
on	O
the	O
typewriter	O
"	O
ENTER	O
SOURCE	O
PROGRAM	O
,	O
PRESS	O
START	O
"	O
Remove	O
Pass	O
I	O
of	O
the	O
compiler	O
from	O
the	O
Read	O
stackerLoad	O
the	O
program	O
source	O
deck	O
(	O
face	O
down	O
9-edge	O
first	O
)	O
into	O
the	O
Read	O
hopper	O
then	O
press	O
StartWait	O
for	O
Pass	O
I	O
to	O
complete	O
and	O
print	O
on	O
the	O
typewriter	O
"	O
TURN	O
SW	O
1	O
ON	O
FOR	O
SYMBOL	O
TABLE	O
,	O
PRESS	O
START	O
"	O
Turn	O
Program	B-Device
Switch	I-Device
1	O
OFF	O
then	O
press	O
StartIf	O
a	O
symbol	O
table	O
listing	O
is	O
desired	O
for	O
debugging	O
,	O
turn	O
Program	B-Device
Switch	I-Device
1	O
ON	O
instead	O
.	O
</s>
<s>
The	O
symbol	O
table	O
listing	O
will	O
be	O
printed	O
on	O
the	O
typewriter.Wait	O
for	O
Pass	O
I	O
to	O
print	O
on	O
the	O
typewriter	O
"	O
END	O
OF	O
PASS	O
1	O
"	O
Set	O
the	O
Program	B-Device
Switches	I-Device
as	O
follows	O
:	O
</s>
<s>
However	O
it	O
was	O
not	O
a	O
complete	O
FORTRAN	B-Application
implementation	O
.	O
</s>
<s>
To	O
improve	O
this	O
various	O
third-party	O
FORTRAN	B-Application
compilers	O
were	O
developed	O
.	O
</s>
<s>
One	O
of	O
these	O
was	O
developed	O
by	O
Bob	O
Richardson	O
,	O
a	O
programmer	O
at	O
Rice	O
University	O
,	O
the	O
FLAG	O
(	O
FORTRAN	B-Application
Load-and-Go	O
)	O
compiler	O
.	O
</s>
<s>
For	O
instance	O
,	O
at	O
Auckland	O
University	O
a	O
batch	O
job	O
processor	O
for	O
student	O
assignments	O
(	O
typically	O
,	O
many	O
small	O
programs	O
not	O
requiring	O
much	O
memory	O
)	O
chugged	O
through	O
a	O
class	O
lot	O
rather	O
faster	O
than	O
the	O
later	O
IBM	B-Device
1130	I-Device
did	O
with	O
its	O
disk-based	O
system	O
.	O
</s>
<s>
The	O
various	O
decks	O
of	O
cards	O
constituting	O
the	O
compiler	O
and	O
loader	O
no	O
longer	O
need	O
be	O
fetched	O
from	O
their	O
cabinets	O
but	O
could	O
be	O
stored	O
on	O
disk	O
and	O
loaded	O
under	O
the	O
control	O
of	O
a	O
simple	O
disk-based	O
operating	B-General_Concept
system	I-General_Concept
:	O
a	O
lot	O
of	O
activity	O
becomes	O
less	O
visible	O
,	O
but	O
still	O
goes	O
on	O
.	O
</s>
<s>
Most	O
of	O
the	O
logic	O
circuitry	O
of	O
the	O
1620	O
was	O
a	O
type	O
of	O
resistor	O
–	O
transistor	B-Application
logic	O
(	O
RTL	O
)	O
using	O
"	O
drift	O
"	O
transistors	B-Application
(	O
a	O
type	O
of	O
transistor	B-Application
invented	O
by	O
Herbert	O
Kroemer	O
in	O
1953	O
)	O
for	O
their	O
speed	O
,	O
that	O
IBM	O
referred	O
to	O
as	O
Saturated	O
Drift	O
Transistor	B-Application
Resistor	O
Logic	O
(	O
SDTRL	O
)	O
.	O
</s>
<s>
Other	O
IBM	O
circuit	O
types	O
used	O
were	O
referred	O
to	O
as	O
:	O
Alloy	O
(	O
some	O
logic	O
,	O
but	O
mostly	O
various	O
non-logic	O
functions	O
,	O
named	O
for	O
the	O
kind	O
of	O
transistors	B-Application
used	O
)	O
,	O
CTRL	O
(	O
another	O
type	O
of	O
RTL	O
,	O
but	O
slower	O
than	O
SDTRL	O
)	O
,	O
CTDL	O
(	O
a	O
type	O
of	O
diode	B-General_Concept
–	I-General_Concept
transistor	I-General_Concept
logic	I-General_Concept
(	O
DTL	B-General_Concept
)	O
)	O
,	O
and	O
DL	O
(	O
another	O
type	O
of	O
RTL	O
,	O
named	O
for	O
the	O
kind	O
of	O
transistor	B-Application
used	O
,	O
"	O
drift	O
"	O
transistors	B-Application
)	O
.	O
</s>
<s>
These	O
circuits	O
were	O
constructed	O
of	O
individual	O
discrete	O
components	O
mounted	O
on	O
single	O
sided	O
paper-epoxy	O
printed	O
circuit	O
boards	O
with	O
a	O
16-pin	O
gold-plated	O
edge	O
connector	O
,	O
that	O
IBM	O
referred	O
to	O
as	O
SMS	O
cards	O
(	O
Standard	B-Device
Modular	I-Device
System	I-Device
)	O
.	O
</s>
<s>
The	O
amount	O
of	O
logic	O
on	O
one	O
card	O
was	O
similar	O
to	O
that	O
in	O
one	O
7400	O
series	O
SSI	O
or	O
simpler	O
MSI	O
package	O
(	O
e.g.	O
,	O
3	O
to	O
5	O
logic	O
gates	O
or	O
a	O
couple	O
of	O
flip-flops	B-General_Concept
)	O
.	O
</s>
<s>
Console	B-Device
Typewriter	O
interface	O
.	O
</s>
<s>
There	O
were	O
two	O
different	O
types	O
of	O
core	B-General_Concept
memory	I-General_Concept
used	O
in	O
the	O
1620	O
:	O
</s>
<s>
The	O
competing	O
computers	O
in	O
this	O
market	O
were	O
the	O
Librascope	B-Device
LGP-30	I-Device
and	O
the	O
Bendix	O
G-15	O
;	O
both	O
were	O
drum	B-General_Concept
memory	I-General_Concept
machines	O
.	O
</s>
<s>
IBM	O
's	O
smallest	O
computer	O
at	O
the	O
time	O
was	O
the	O
popular	O
IBM	O
650	O
,	O
a	O
fixed	O
word	O
length	O
decimal	O
machine	O
that	O
also	O
used	O
drum	B-General_Concept
memory	I-General_Concept
.	O
</s>
<s>
Management	O
was	O
not	O
entirely	O
convinced	O
that	O
core	B-General_Concept
memory	I-General_Concept
could	O
be	O
made	O
to	O
work	O
in	O
small	O
machines	O
,	O
so	O
Gerry	O
Ottaway	O
was	O
loaned	O
to	O
the	O
team	O
to	O
design	O
a	O
drum	B-General_Concept
memory	I-General_Concept
as	O
a	O
backup	O
.	O
</s>
<s>
During	O
acceptance	O
testing	O
by	O
the	O
Product	O
Test	O
Lab	O
,	O
repeated	O
core	B-General_Concept
memory	I-General_Concept
failures	O
were	O
encountered	O
and	O
it	O
looked	O
likely	O
that	O
management	O
's	O
predictions	O
would	O
come	O
true	O
.	O
</s>
<s>
However	O
,	O
at	O
the	O
last	O
minute	O
it	O
was	O
found	O
that	O
the	O
muffin	B-Application
fan	I-Application
used	O
to	O
blow	O
hot	O
air	O
through	O
the	O
core	O
stack	O
was	O
malfunctioning	O
,	O
causing	O
the	O
core	O
to	O
pick	O
up	O
noise	O
pulses	O
and	O
fail	O
to	O
read	O
correctly	O
.	O
</s>
<s>
After	O
the	O
fan	O
problem	O
was	O
fixed	O
,	O
there	O
were	O
no	O
further	O
problems	O
with	O
the	O
core	B-General_Concept
memory	I-General_Concept
and	O
the	O
drum	B-General_Concept
memory	I-General_Concept
design	O
effort	O
was	O
discontinued	O
as	O
unnecessary	O
.	O
</s>
<s>
Following	O
announcement	O
of	O
the	O
IBM	B-Device
1620	I-Device
on	O
October	O
21	O
,	O
1959	O
,	O
due	O
to	O
an	O
internal	O
reorganization	O
of	O
IBM	O
,	O
it	O
was	O
decided	O
to	O
transfer	O
the	O
computer	O
from	O
the	O
Data	O
Processing	O
Division	O
at	O
Poughkeepsie	O
(	O
large	O
scale	O
mainframe	O
computers	O
only	O
)	O
to	O
the	O
General	O
Products	O
Division	O
at	O
San	O
Jose	O
(	O
small	O
computers	O
and	O
support	O
products	O
only	O
)	O
for	O
manufacturing	O
.	O
</s>
<s>
All	O
flip-flops	B-General_Concept
in	O
the	O
design	O
were	O
transistorized	O
versions	O
of	O
the	O
original	O
Eccles-Jordan	O
trigger	O
circuit	O
.	O
</s>
<s>
While	O
this	O
machine	O
was	O
fully	O
functional	O
,	O
it	O
was	O
found	O
that	O
the	O
capacitor	O
coupling	O
used	O
in	O
these	O
proved	O
troublesome	O
in	O
the	O
noisy	O
signal	O
environment	O
of	O
relays	O
and	O
timing	O
cam	B-Data_Structure
driven	O
switches	O
used	O
to	O
drive	O
the	O
console	B-Device
typewriter	O
.	O
</s>
<s>
This	O
necessitated	O
a	O
complete	O
redesign	O
of	O
the	O
machine	O
to	O
use	O
S-R	O
flip-flops	B-General_Concept
instead	O
(	O
except	O
for	O
two	O
triggers	O
used	O
to	O
generate	O
clocks	O
for	O
the	O
S-R	O
flip-flops	B-General_Concept
)	O
.	O
</s>
<s>
However	O
usage	O
of	O
the	O
term	O
Trigger	O
was	O
retained	O
in	O
all	O
the	O
documentation	O
when	O
referring	O
to	O
a	O
flip-flop	B-General_Concept
,	O
as	O
it	O
was	O
IBM	O
's	O
conventional	O
term	O
(	O
as	O
alphamerics	O
was	O
their	O
term	O
for	O
alphanumerics	O
)	O
.	O
</s>
<s>
Level	O
D	O
;	O
introduction	O
of	O
1311	B-Device
disk	O
drives	O
and	O
addition	O
of	O
optional	O
"	O
Gate	O
J	O
"	O
containing	O
disk	O
control	O
logic	O
.	O
</s>
<s>
Level	O
E	O
;	O
introduction	O
of	O
Floating	B-Algorithm
Point	I-Algorithm
option	O
.	O
</s>
<s>
Level	O
G	O
;	O
introduction	O
of	O
Interrupt	O
option	O
(	O
needed	O
for	O
IBM	B-Device
1710	I-Device
)	O
.	O
</s>
<s>
The	O
1620	O
Model	O
II	O
introduced	O
basic	O
ALU	B-General_Concept
hardware	O
for	O
addition	O
and	O
subtraction	O
(	O
making	O
"	O
Ca	O
n't	O
Add	O
,	O
Does	O
n't	O
Even	O
Try	O
"	O
no	O
longer	O
applicable	O
)	O
and	O
index	B-General_Concept
registers	I-General_Concept
.	O
</s>
<s>
Work	O
was	O
begun	O
on	O
a	O
1620	O
Model	O
III	O
but	O
the	O
project	O
was	O
quickly	O
canceled	O
as	O
IBM	O
wanted	O
to	O
promote	O
sales	O
of	O
their	O
new	O
System/360	B-Application
and	O
discontinue	O
the	O
old	O
lines	O
.	O
</s>
<s>
An	O
IBM	B-Device
1620	I-Device
model	O
II	O
was	O
used	O
by	O
Vearl	O
N	O
.	O
Huff	O
,	O
NASA	O
Headquarters	O
(	O
FOB	O
10B	O
,	O
Washington	O
DC	O
)	O
to	O
program	O
a	O
three-dimensional	O
simulation	O
in	O
Fortran	B-Application
of	O
the	O
tethered	O
Gemini	O
capsule	O
Agena	O
rocket	O
module	O
two-body	O
problem	O
at	O
a	O
time	O
when	O
it	O
was	O
not	O
completely	O
understood	O
if	O
it	O
was	O
safe	O
to	O
tether	O
two	O
objects	O
together	O
in	O
space	O
due	O
to	O
possible	O
elastic	O
tether	O
induced	O
collisions	O
.	O
</s>
<s>
In	O
1963	O
an	O
IBM	B-Device
1620	I-Device
was	O
installed	O
at	O
IIT	O
Kanpur	O
providing	O
the	O
kicker	O
for	O
India	O
's	O
software	O
prowess	O
.	O
</s>
<s>
In	O
1964	O
at	O
the	O
Australian	O
National	O
University	O
,	O
Martin	O
Ward	O
used	O
an	O
IBM	B-Device
1620	I-Device
model	O
I	O
to	O
calculate	O
the	O
order	O
of	O
the	O
Janko	O
group	O
J1	O
.	O
</s>
<s>
In	O
1966	O
the	O
ITU	O
produced	O
an	O
explanatory	O
film	O
on	O
a	O
1963	O
system	O
for	O
typesetting	O
by	O
computer	O
at	O
the	O
Washington	O
Evening	O
Star	O
,	O
using	O
an	O
IBM	B-Device
1620	I-Device
and	O
a	O
Linofilm	O
phototypesetter	O
.	O
</s>
<s>
In	O
1964	O
an	O
IBM	B-Device
1620	I-Device
was	O
installed	O
at	O
The	O
University	O
of	O
Iceland	O
,	O
becoming	O
the	O
first	O
computer	O
in	O
Iceland	O
.	O
</s>
<s>
The	O
fictional	O
computer	O
Colossus	O
of	O
Colossus	O
:	O
The	O
Forbin	O
Project	O
used	O
about	O
a	O
dozen	O
scrapped	O
1620	O
front	B-Device
panels	I-Device
purchased	O
on	O
the	O
surplus	O
market	O
,	O
in	O
various	O
orientations	O
.	O
</s>
<s>
One	O
of	O
the	O
developers	O
says	O
that	O
this	O
stood	O
for	O
"	O
Computer	O
with	O
ADvanced	O
Economic	O
Technology	O
"	O
,	O
however	O
others	O
recall	O
it	O
as	O
simply	O
being	O
one	O
half	O
of	O
"	O
SPACE	O
-	O
CADET	O
"	O
,	O
where	O
SPACE	O
was	O
the	O
internal	O
code	O
name	O
of	O
the	O
IBM	B-Device
1401	I-Device
machine	O
,	O
also	O
then	O
under	O
development	O
.	O
</s>
