<s>
The	O
CDC	B-Device
6600	I-Device
was	O
the	O
flagship	O
of	O
the	O
6000	B-Device
series	I-Device
of	O
mainframe	B-Architecture
computer	I-Architecture
systems	O
manufactured	O
by	O
Control	O
Data	O
Corporation	O
.	O
</s>
<s>
Generally	O
considered	O
to	O
be	O
the	O
first	O
successful	O
supercomputer	B-Architecture
,	O
it	O
outperformed	O
the	O
industry	O
's	O
prior	O
recordholder	O
,	O
the	O
IBM	B-Device
7030	I-Device
Stretch	I-Device
,	O
by	O
a	O
factor	O
of	O
three	O
.	O
</s>
<s>
With	O
performance	O
of	O
up	O
to	O
threemegaFLOPS	O
,	O
the	O
CDC	B-Device
6600	I-Device
was	O
the	O
world	O
's	O
fastest	O
computer	O
from	O
1964	O
to	O
1969	O
,	O
when	O
it	O
relinquished	O
that	O
status	O
to	O
its	O
successor	O
,	O
the	O
CDC	B-Device
7600	I-Device
.	O
</s>
<s>
The	O
first	O
CDC	B-Device
6600s	I-Device
were	O
delivered	O
in	O
1965	O
to	O
Livermore	O
and	O
Los	O
Alamos	O
.	O
</s>
<s>
A	O
CDC	B-Device
6600	I-Device
is	O
on	O
display	O
at	O
the	O
Computer	O
History	O
Museum	O
in	O
Mountain	O
View	O
,	O
California	O
.	O
</s>
<s>
The	O
only	O
running	O
CDC	B-Device
6000	I-Device
series	I-Device
machine	O
has	O
been	O
restored	O
by	O
Living	O
Computers	O
:	O
Museum	O
+	O
Labs	O
.	O
</s>
<s>
After	O
an	O
experimental	O
machine	O
known	O
as	O
the	O
Little	O
Character	O
,	O
in	O
1960	O
they	O
delivered	O
the	O
CDC	B-Device
1604	I-Device
,	O
one	O
of	O
the	O
first	O
commercial	O
transistor-based	B-Device
computers	I-Device
,	O
and	O
one	O
of	O
the	O
fastest	O
machines	O
on	O
the	O
market	O
.	O
</s>
<s>
Taking	O
his	O
core	O
team	O
to	O
new	O
offices	O
nearby	O
the	O
original	O
CDC	O
headquarters	O
,	O
they	O
started	O
to	O
experiment	O
with	O
higher	O
quality	O
versions	O
of	O
the	O
"	O
cheap	O
"	O
transistors	B-Application
Cray	O
had	O
used	O
in	O
the	O
1604	O
.	O
</s>
<s>
After	O
much	O
experimentation	O
,	O
they	O
found	O
that	O
there	O
was	O
simply	O
no	O
way	O
the	O
germanium-based	O
transistors	B-Application
could	O
be	O
run	O
much	O
faster	O
than	O
those	O
used	O
in	O
the	O
1604	O
.	O
</s>
<s>
The	O
"	O
business	O
machine	O
"	O
that	O
management	O
had	O
originally	O
wanted	O
,	O
now	O
forming	O
as	O
the	O
CDC	B-Device
3000	I-Device
series	I-Device
,	O
pushed	O
them	O
about	O
as	O
far	O
as	O
they	O
could	O
go	O
.	O
</s>
<s>
Cray	O
then	O
decided	O
the	O
solution	O
was	O
to	O
work	O
with	O
the	O
then-new	O
silicon-based	O
transistors	B-Application
from	O
Fairchild	O
Semiconductor	O
,	O
which	O
were	O
just	O
coming	O
onto	O
the	O
market	O
and	O
offered	O
dramatically	O
improved	O
switching	O
performance	O
.	O
</s>
<s>
Things	O
became	O
considerably	O
more	O
tense	O
in	O
1962	O
when	O
the	O
new	O
CDC	B-Device
3600	I-Device
started	O
to	O
near	O
production	O
quality	O
,	O
and	O
appeared	O
to	O
be	O
exactly	O
what	O
management	O
wanted	O
,	O
when	O
they	O
wanted	O
it	O
.	O
</s>
<s>
By	O
this	O
time	O
,	O
the	O
new	O
transistors	B-Application
were	O
becoming	O
quite	O
reliable	O
,	O
and	O
modules	O
built	O
with	O
them	O
tended	O
to	O
work	O
properly	O
on	O
the	O
first	O
try	O
.	O
</s>
<s>
More	O
than	O
100	O
CDC	B-Device
6600s	I-Device
were	O
sold	O
over	O
the	O
machine	O
's	O
lifetime	O
.	O
</s>
<s>
Cray	O
immediately	O
turned	O
his	O
attention	O
to	O
its	O
replacement	O
,	O
this	O
time	O
setting	O
a	O
goal	O
of	O
ten	O
times	O
the	O
performance	O
of	O
the	O
6600	O
,	O
delivered	O
as	O
the	O
CDC	B-Device
7600	I-Device
.	O
</s>
<s>
The	O
later	O
CDC	B-Device
Cyber	I-Device
70	I-Device
and	O
170	O
computers	O
were	O
very	O
similar	O
to	O
the	O
CDC	B-Device
6600	I-Device
in	O
overall	O
design	O
and	O
were	O
nearly	O
completely	O
backwards	O
compatible	O
.	O
</s>
<s>
The	O
6600	O
was	O
three	O
times	O
faster	O
than	O
the	O
previous	O
record-holder	O
,	O
the	O
IBM	B-Device
7030	I-Device
Stretch	I-Device
;	O
this	O
alarmed	O
IBM	O
.	O
</s>
<s>
Typical	O
machines	O
of	O
the	O
1950s	O
and	O
1960s	O
used	O
a	O
single	O
central	B-General_Concept
processing	I-General_Concept
unit	I-General_Concept
(	O
CPU	O
)	O
to	O
drive	O
the	O
entire	O
system	O
.	O
</s>
<s>
The	O
CDC	B-Device
6600	I-Device
used	O
a	O
simplified	O
central	O
processor	O
(	O
CP	O
)	O
that	O
was	O
designed	O
to	O
run	O
mathematical	O
and	O
logic	O
operations	O
as	O
rapidly	O
as	O
possible	O
,	O
which	O
demanded	O
it	O
be	O
built	O
as	O
small	O
as	O
possible	O
to	O
reduce	O
the	O
length	O
of	O
wiring	O
and	O
the	O
associated	O
signalling	O
delays	O
.	O
</s>
<s>
Combined	O
with	O
the	O
faster	O
switching	O
speeds	O
of	O
the	O
silicon	O
transistors	B-Application
,	O
the	O
new	O
CPU	O
ran	O
at	O
10MHz	O
(	O
100ns	O
cycle	O
time	O
)	O
,	O
about	O
ten	O
times	O
faster	O
than	O
other	O
machines	O
on	O
the	O
market	O
.	O
</s>
<s>
Supporting	O
the	O
CPU	O
were	O
ten	O
12-bit	B-Device
4	O
KiB	O
peripheral	O
processors	O
(	O
PPs	O
)	O
,	O
each	O
with	O
access	O
to	O
a	O
common	O
pool	O
of	O
12	O
input/output	B-General_Concept
(	O
I/O	B-General_Concept
)	O
channels	B-Device
,	O
that	O
handled	O
input	B-General_Concept
and	I-General_Concept
output	I-General_Concept
,	O
as	O
well	O
as	O
controlling	O
what	O
data	O
were	O
sent	O
into	O
central	O
memory	O
for	O
processing	O
by	O
the	O
CP	O
.	O
</s>
<s>
This	O
allowed	O
them	O
to	O
perform	O
input/output	B-General_Concept
essentially	O
for	O
free	O
in	O
terms	O
of	O
central	O
processing	O
time	O
,	O
keeping	O
the	O
CPU	O
busy	O
as	O
much	O
as	O
possible	O
.	O
</s>
<s>
The	O
6600	O
's	O
CP	O
used	O
a	O
60-bit	B-Device
word	O
and	O
a	O
ones	O
 '	O
complement	O
representation	O
of	O
integers	O
,	O
something	O
that	O
later	O
CDC	O
machines	O
would	O
use	O
into	O
the	O
late	O
1980s	O
,	O
making	O
them	O
the	O
last	O
systems	O
besides	O
some	O
digital	B-Architecture
signal	I-Architecture
processors	I-Architecture
to	O
use	O
this	O
architecture	B-General_Concept
.	O
</s>
<s>
Later	O
,	O
CDC	O
offered	O
options	O
as	O
to	O
the	O
number	O
and	O
type	O
of	O
CPs	O
,	O
PPs	O
and	O
channels	B-Device
,	O
e.g.	O
,	O
the	O
CDC	O
6700	O
had	O
a	O
6400	O
CP	O
and	O
a	O
6600	O
CP	O
.	O
</s>
<s>
The	O
entire	O
6600	O
machine	O
contained	O
approximately	O
400,000	O
transistors	B-Application
.	O
</s>
<s>
A	O
typical	O
CPU	O
of	O
the	O
era	O
had	O
a	O
complex	B-Architecture
instruction	I-Architecture
set	I-Architecture
,	O
which	O
included	O
instructions	O
to	O
handle	O
all	O
the	O
normal	O
"	O
housekeeping	O
"	O
tasks	O
,	O
such	O
as	O
memory	O
access	O
and	O
input/output	B-General_Concept
.	O
</s>
<s>
This	O
was	O
the	O
first	O
of	O
what	O
later	O
came	O
to	O
be	O
called	O
reduced	B-Architecture
instruction	I-Architecture
set	I-Architecture
computer	I-Architecture
(	O
RISC	B-Architecture
)	O
design	O
.	O
</s>
<s>
By	O
allowing	O
the	O
CPU	O
,	O
peripheral	O
processors	O
(	O
PPs	O
)	O
and	O
I/O	B-General_Concept
to	O
operate	O
in	O
parallel	B-Operating_System
,	O
the	O
design	O
considerably	O
improved	O
the	O
performance	O
of	O
the	O
machine	O
.	O
</s>
<s>
Key	O
to	O
the	O
6600	O
's	O
design	O
was	O
to	O
make	O
the	O
I/O	B-Device
processors	I-Device
,	O
known	O
as	O
peripheral	O
processors	O
(	O
PPs	O
)	O
,	O
as	O
simple	O
as	O
possible	O
.	O
</s>
<s>
The	O
PPs	O
were	O
based	O
on	O
the	O
simple	O
12-bit	B-Device
CDC	B-Device
160-A	I-Device
,	O
which	O
ran	O
much	O
slower	O
than	O
the	O
CPU	O
,	O
gathering	O
up	O
data	O
and	O
transmitting	O
it	O
as	O
bursts	B-Architecture
into	O
main	O
memory	O
at	O
high	O
speed	O
via	O
dedicated	O
hardware	O
.	O
</s>
<s>
This	O
CPU	O
hardware	O
was	O
shared	O
and	O
operated	O
on	O
10	O
PP	O
register	O
sets	O
which	O
represented	O
each	O
of	O
the	O
10	O
PP	O
states	O
(	O
similar	O
to	O
modern	O
multithreading	B-Operating_System
processors	O
)	O
.	O
</s>
<s>
The	O
PP	O
register	B-Operating_System
barrel	I-Operating_System
would	O
"	O
rotate	O
"	O
,	O
with	O
each	O
PP	O
register	O
set	O
presented	O
to	O
the	O
"	O
slot	O
"	O
which	O
the	O
actual	O
PP	O
CPU	O
occupied	O
.	O
</s>
<s>
The	O
basis	O
for	O
the	O
6600	O
CPU	O
is	O
what	O
would	O
later	O
be	O
called	O
a	O
RISC	B-Architecture
system	O
,	O
one	O
in	O
which	O
the	O
processor	O
is	O
tuned	O
to	O
do	O
instructions	O
which	O
are	O
comparatively	O
simple	O
and	O
have	O
limited	O
and	O
well-defined	O
access	O
to	O
memory	O
.	O
</s>
<s>
While	O
slower	O
in	O
theory	O
due	O
to	O
the	O
additional	O
memory	O
accesses	O
,	O
the	O
fact	O
that	O
in	O
well-scheduled	O
code	O
,	O
multiple	O
instructions	O
could	O
be	O
processing	O
in	O
parallel	B-Operating_System
offloaded	O
this	O
expense	O
.	O
</s>
<s>
The	O
CDC	B-Device
6000	I-Device
series	I-Device
included	O
four	O
basic	O
models	O
,	O
the	O
CDC	O
6400	O
,	O
the	O
CDC	O
6500	O
,	O
the	O
CDC	B-Device
6600	I-Device
,	O
and	O
the	O
CDC	O
6700	O
.	O
</s>
<s>
The	O
models	O
of	O
the	O
6000	B-Device
series	I-Device
differed	O
only	O
in	O
their	O
CPUs	O
,	O
which	O
were	O
of	O
two	O
kinds	O
,	O
the	O
6400	O
CPU	O
and	O
the	O
6600	O
CPU	O
.	O
</s>
<s>
The	O
6400	O
CPU	O
had	O
a	O
unified	O
arithmetic	O
unit	O
,	O
rather	O
than	O
discrete	O
functional	B-General_Concept
units	I-General_Concept
.	O
</s>
<s>
The	O
6600	O
CPU	O
had	O
multiple	O
functional	B-General_Concept
units	I-General_Concept
which	O
could	O
operate	O
simultaneously	O
,	O
i.e.	O
,	O
"	O
in	O
parallel	B-Operating_System
"	O
,	O
allowing	O
the	O
CPU	O
to	O
overlap	O
instructions	O
 '	O
execution	O
times	O
.	O
</s>
<s>
The	O
6600	O
CPU	O
also	O
had	O
an	O
instruction	O
stack	O
,	O
a	O
kind	O
of	O
instruction	O
cache	B-General_Concept
,	O
which	O
helped	O
increase	O
CPU	O
throughput	O
by	O
reducing	O
the	O
amount	O
of	O
CPU	O
idle	O
time	O
caused	O
by	O
waiting	O
for	O
memory	O
to	O
respond	O
to	O
instruction	O
fetch	O
requests	O
.	O
</s>
<s>
Indeed	O
,	O
all	O
models	O
of	O
the	O
6000	B-Device
series	I-Device
were	O
fully	O
inter-compatible	O
.	O
</s>
<s>
The	O
CDC	O
6400	O
had	O
one	O
CPU	O
(	O
a	O
6400	O
CPU	O
)	O
,	O
the	O
CDC	O
6500	O
had	O
two	O
CPUs	O
(	O
both	O
6400	O
CPUs	O
)	O
,	O
the	O
CDC	B-Device
6600	I-Device
had	O
one	O
CPU	O
(	O
a	O
6600	O
CPU	O
)	O
,	O
and	O
the	O
CDC	O
6700	O
had	O
two	O
CPUs	O
(	O
one	O
6600	O
CPU	O
and	O
one	O
6400	O
CPU	O
)	O
.	O
</s>
<s>
+	O
CDC	O
6x00	O
registers	B-General_Concept
59	O
.	O
</s>
<s>
The	O
Central	O
Processor	O
(	O
CP	O
)	O
and	O
main	O
memory	O
of	O
the	O
6400	O
,	O
6500	O
,	O
and	O
6600	O
machines	O
had	O
a	O
60-bit	B-Device
word	O
length	O
.	O
</s>
<s>
The	O
Central	O
Processor	O
had	O
eight	O
general	O
purpose	O
60-bit	B-Device
registers	B-General_Concept
X0	O
through	O
X7	O
,	O
eight	O
18-bit	B-General_Concept
address	B-General_Concept
registers	I-General_Concept
A0	O
through	O
A7	O
,	O
and	O
eight	O
18-bit	B-General_Concept
"	O
increment	O
"	O
registers	B-General_Concept
B0	O
through	O
B7	O
.	O
</s>
<s>
The	O
CP	O
had	O
no	O
instructions	O
for	O
input	B-General_Concept
and	I-General_Concept
output	I-General_Concept
,	O
which	O
are	O
accomplished	O
through	O
Peripheral	O
Processors	O
(	O
below	O
)	O
.	O
</s>
<s>
No	O
opcodes	O
were	O
specifically	O
dedicated	O
to	O
loading	O
or	O
storing	O
memory	O
;	O
this	O
occurred	O
as	O
a	O
side	O
effect	O
of	O
assignment	O
to	O
certain	O
A	O
registers	B-General_Concept
.	O
</s>
<s>
The	O
6600	O
CP	O
included	O
ten	O
parallel	B-Operating_System
functional	B-General_Concept
units	I-General_Concept
,	O
allowing	O
multiple	O
instructions	O
to	O
be	O
worked	O
on	O
at	O
the	O
same	O
time	O
.	O
</s>
<s>
Today	O
,	O
this	O
is	O
known	O
as	O
a	O
superscalar	B-General_Concept
processor	I-General_Concept
design	O
,	O
but	O
it	O
was	O
unique	O
for	O
its	O
time	O
.	O
</s>
<s>
Unlike	O
most	O
modern	O
CPU	O
designs	O
,	O
functional	B-General_Concept
units	I-General_Concept
were	O
not	O
pipelined	O
;	O
the	O
functional	B-General_Concept
unit	I-General_Concept
would	O
become	O
busy	O
when	O
an	O
instruction	O
was	O
"	O
issued	O
"	O
to	O
it	O
and	O
would	O
remain	O
busy	O
for	O
the	O
entire	O
time	O
required	O
to	O
execute	O
that	O
instruction	O
.	O
</s>
<s>
(	O
By	O
contrast	O
,	O
the	O
CDC	B-Device
7600	I-Device
introduced	O
pipelining	O
into	O
its	O
functional	B-General_Concept
units	I-General_Concept
.	O
)	O
</s>
<s>
In	O
the	O
best	O
case	O
,	O
an	O
instruction	O
could	O
be	O
issued	O
to	O
a	O
functional	B-General_Concept
unit	I-General_Concept
every	O
100ns	O
clock	O
cycle	O
.	O
</s>
<s>
Floating-point	B-Algorithm
operations	O
were	O
given	O
pride	O
of	O
place	O
in	O
this	O
architecture	B-General_Concept
:	O
the	O
CDC	B-Device
6600	I-Device
(	O
and	O
kin	O
)	O
stand	O
virtually	O
alone	O
in	O
being	O
able	O
to	O
execute	O
a	O
60-bit	B-Device
floating	B-Algorithm
point	I-Algorithm
multiplication	O
in	O
time	O
comparable	O
to	O
that	O
for	O
a	O
program	O
branch	O
.	O
</s>
<s>
revealed	O
that	O
the	O
6600	O
's	O
Floating	B-Algorithm
Point	I-Algorithm
unit	O
is	O
a	O
2	O
stage	O
pipelined	O
design	O
.	O
</s>
<s>
Fixed	O
point	O
addition	O
and	O
subtraction	O
of	O
60-bit	B-Device
numbers	O
were	O
handled	O
in	O
the	O
Long	O
Add	O
Unit	O
,	O
using	O
ones	O
 '	O
complement	O
for	O
negative	O
numbers	O
.	O
</s>
<s>
Fixed	O
point	O
multiply	O
was	O
done	O
as	O
a	O
special	O
case	O
in	O
the	O
floating-point	B-Algorithm
multiply	O
unit	O
—	O
if	O
the	O
exponent	O
was	O
zero	O
,	O
the	O
FP	O
unit	O
would	O
do	O
a	O
single-precision	O
48-bit	O
floating-point	B-Algorithm
multiply	O
and	O
clear	O
the	O
high	O
exponent	O
part	O
,	O
resulting	O
in	O
a	O
48-bit	O
integer	O
result	O
.	O
</s>
<s>
Integer	O
divide	O
was	O
performed	O
by	O
a	O
macro	O
,	O
converting	O
to	O
and	O
from	O
floating	B-Algorithm
point	I-Algorithm
.	O
</s>
<s>
Previously	O
executed	O
instructions	O
were	O
saved	O
in	O
an	O
eight-word	O
cache	B-General_Concept
,	O
called	O
the	O
"	O
stack	O
"	O
.	O
</s>
<s>
A	O
floating-point	B-Algorithm
multiplication	O
took	O
ten	O
cycles	O
,	O
a	O
division	O
took	O
29	O
,	O
and	O
the	O
overall	O
performance	O
,	O
taking	O
into	O
account	O
memory	O
delays	O
and	O
other	O
issues	O
,	O
was	O
about	O
3MFLOPS	O
.	O
</s>
<s>
Using	O
the	O
best	O
available	O
compilers	O
,	O
late	O
in	O
the	O
machine	O
's	O
history	O
,	O
FORTRAN	B-Application
programs	O
could	O
expect	O
to	O
maintain	O
about	O
0.5MFLOPS	O
.	O
</s>
<s>
The	O
portion	O
of	O
memory	O
to	O
which	O
an	O
executing	O
program	O
has	O
access	O
is	O
controlled	O
by	O
the	O
RA	O
(	O
Relative	O
Address	O
)	O
and	O
FL	O
(	O
Field	O
Length	O
)	O
registers	B-General_Concept
which	O
are	O
not	O
accessible	O
to	O
the	O
user	O
program	O
.	O
</s>
<s>
Using	O
this	O
technique	O
,	O
each	O
user	O
program	O
can	O
be	O
moved	O
(	O
"	O
relocated	O
"	O
)	O
in	O
main	O
memory	O
by	O
the	O
operating	B-General_Concept
system	I-General_Concept
,	O
as	O
long	O
as	O
the	O
RA	O
register	O
reflects	O
its	O
position	O
in	O
memory	O
.	O
</s>
<s>
A	O
user	O
program	O
which	O
attempts	O
to	O
access	O
memory	O
outside	O
the	O
allowed	O
range	O
(	O
that	O
is	O
,	O
with	O
an	O
address	O
which	O
is	O
not	O
less	O
than	O
FL	O
)	O
will	O
trigger	O
an	O
interrupt	O
,	O
and	O
will	O
be	O
terminated	O
by	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
When	O
this	O
happens	O
,	O
the	O
operating	B-General_Concept
system	I-General_Concept
may	O
create	O
a	O
core	B-Error_Name
dump	I-Error_Name
which	O
records	O
the	O
contents	O
of	O
the	O
program	O
's	O
memory	O
and	O
registers	B-General_Concept
in	O
a	O
file	O
,	O
allowing	O
the	O
developer	O
of	O
the	O
program	O
a	O
means	O
to	O
know	O
what	O
happened	O
.	O
</s>
<s>
Note	O
the	O
distinction	O
with	O
virtual	B-Architecture
memory	I-Architecture
systems	O
;	O
in	O
this	O
case	O
,	O
the	O
entirety	O
of	O
a	O
process	O
's	O
addressable	O
space	O
must	O
be	O
in	O
core	O
memory	O
,	O
must	O
be	O
contiguous	O
,	O
and	O
its	O
size	O
cannot	O
be	O
larger	O
than	O
the	O
real	O
memory	O
capacity	O
.	O
</s>
<s>
All	O
but	O
the	O
first	O
seven	O
CDC	B-Device
6000	I-Device
series	I-Device
machines	O
could	O
be	O
configured	O
with	O
an	O
optional	O
Extended	O
Core	O
Storage	O
(	O
ECS	O
)	O
system	O
.	O
</s>
<s>
A	O
6000	O
CPU	O
could	O
directly	O
perform	O
block	O
memory	O
transfers	O
between	O
a	O
user	O
's	O
program	O
(	O
or	O
operating	B-General_Concept
system	I-General_Concept
)	O
and	O
the	O
ECS	O
unit	O
.	O
</s>
<s>
Memory	O
bounds	O
were	O
maintained	O
in	O
a	O
similar	O
manner	O
as	O
central	O
memory	O
,	O
with	O
an	O
RA/FL	O
mechanism	O
maintained	O
by	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
ECS	O
could	O
be	O
used	O
for	O
a	O
variety	O
of	O
purposes	O
,	O
including	O
containing	O
user	O
data	O
arrays	O
that	O
were	O
too	O
large	O
for	O
central	O
memory	O
,	O
holding	O
often-used	O
files	O
,	O
swapping	O
,	O
and	O
even	O
as	O
a	O
communication	O
path	O
in	O
a	O
multi-mainframe	O
complex	O
.	O
</s>
<s>
To	O
handle	O
the	O
"	O
housekeeping	O
"	O
tasks	O
,	O
which	O
in	O
other	O
designs	O
were	O
assigned	O
to	O
the	O
CPU	O
,	O
Cray	O
included	O
ten	O
other	O
processors	O
,	O
based	O
partly	O
on	O
his	O
earlier	O
computer	O
,	O
the	O
CDC	B-Device
160-A	I-Device
.	O
</s>
<s>
These	O
machines	O
,	O
called	O
Peripheral	O
Processors	O
,	O
or	O
PPs	O
,	O
were	O
full	O
computers	O
in	O
their	O
own	O
right	O
,	O
but	O
were	O
tuned	O
to	O
performing	O
I/O	B-General_Concept
tasks	O
and	O
running	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
(	O
Substantial	O
parts	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
ran	O
on	O
the	O
PP	O
's	O
;	O
thus	O
leaving	O
most	O
of	O
the	O
power	O
of	O
the	O
Central	O
Processor	O
available	O
for	O
user	O
programs	O
.	O
)	O
</s>
<s>
Only	O
the	O
PPs	O
had	O
access	O
to	O
the	O
I/O	B-Device
channels	I-Device
.	O
</s>
<s>
One	O
of	O
the	O
PPs	O
(	O
PP0	O
)	O
was	O
in	O
overall	O
control	O
of	O
the	O
machine	O
,	O
including	O
control	O
of	O
the	O
program	O
running	O
on	O
the	O
main	O
CPU	O
,	O
while	O
the	O
others	O
would	O
be	O
dedicated	O
to	O
various	O
I/O	B-General_Concept
tasks	O
;	O
PP9	O
was	O
dedicated	O
to	O
the	O
system	B-Device
console	I-Device
.	O
</s>
<s>
When	O
the	O
CP	O
program	O
needed	O
to	O
perform	O
an	O
operating	B-General_Concept
system	I-General_Concept
function	O
,	O
it	O
would	O
put	O
a	O
request	O
in	O
a	O
known	O
location	O
(	O
Reference	O
Address	O
+	O
1	O
)	O
monitored	O
by	O
PP0	O
.	O
</s>
<s>
Each	O
PP	O
included	O
its	O
own	O
memory	O
of	O
4096	O
12-bit	B-Device
words	O
.	O
</s>
<s>
This	O
memory	O
served	O
for	O
both	O
for	O
I/O	B-General_Concept
buffering	O
and	O
program	O
storage	O
,	O
but	O
the	O
execution	B-General_Concept
units	I-General_Concept
were	O
shared	O
by	O
ten	O
PPs	O
,	O
in	O
a	O
configuration	O
called	O
the	O
Barrel	B-Operating_System
and	I-Operating_System
slot	I-Operating_System
.	O
</s>
<s>
This	O
meant	O
that	O
the	O
execution	B-General_Concept
units	I-General_Concept
(	O
the	O
"	O
slot	O
"	O
)	O
would	O
execute	O
one	O
instruction	O
cycle	O
from	O
the	O
first	O
PP	O
,	O
then	O
one	O
instruction	O
cycle	O
from	O
the	O
second	O
PP	O
,	O
etc	O
.	O
</s>
<s>
CRD	O
d	O
-	O
transfers	O
one	O
60-bit	B-Device
word	O
from	O
central	O
memory	O
at	O
the	O
address	O
specified	O
by	O
the	O
PPs	O
A	O
register	O
to	O
five	O
consecutive	O
PP	O
words	O
beginning	O
at	O
address	O
d	O
.	O
</s>
<s>
RPN	O
-	O
transfers	O
the	O
contents	O
of	O
the	O
central	O
processor	O
's	O
program	O
address	B-General_Concept
register	I-General_Concept
to	O
the	O
PP	O
's	O
A	O
register	O
.	O
</s>
<s>
The	O
CP	O
Exchange	O
Jump	O
interrupts	O
the	O
processor	O
,	O
loads	O
its	O
registers	B-General_Concept
from	O
the	O
specified	O
location	O
and	O
stores	O
the	O
previous	O
contents	O
at	O
the	O
same	O
location	O
.	O
</s>
<s>
The	O
central	O
processor	O
has	O
60-bit	B-Device
words	O
,	O
while	O
the	O
peripheral	O
processors	O
have	O
12-bit	B-Device
words	O
.	O
</s>
<s>
CDC	O
used	O
the	O
term	O
"	O
byte	O
"	O
to	O
refer	O
to	O
12-bit	B-Device
entities	O
used	O
by	O
peripheral	O
processors	O
;	O
characters	O
are	O
6-bit	O
,	O
and	O
central	O
processor	O
instructions	O
are	O
either	O
15	O
bits	O
,	O
or	O
30	O
bits	O
with	O
a	O
signed	O
18-bit	B-General_Concept
address	O
field	O
,	O
the	O
latter	O
allowing	O
for	O
a	O
directly	O
addressable	O
memory	O
space	O
of	O
128K	O
words	O
of	O
central	O
memory	O
(	O
converted	O
to	O
modern	O
terms	O
,	O
with	O
8-bit	O
bytes	O
,	O
this	O
just	O
under	O
1MB	O
)	O
.	O
</s>
<s>
The	O
signed	O
nature	O
of	O
the	O
address	B-General_Concept
registers	I-General_Concept
limits	O
an	O
individual	O
program	O
to	O
128K	O
words	O
.	O
</s>
<s>
Experienced	O
assembler	B-Language
programmers	O
could	O
fine-tune	O
their	O
programs	O
by	O
filling	O
these	O
no-op	O
spaces	O
with	O
misc	O
instructions	O
that	O
would	O
be	O
needed	O
later	O
in	O
the	O
program	O
.	O
</s>
<s>
The	O
6-bit	O
characters	O
,	O
in	O
an	O
encoding	O
called	O
CDC	B-Application
display	I-Application
code	I-Application
,	O
could	O
be	O
used	O
to	O
store	O
up	O
to	O
10	O
characters	O
in	O
a	O
word	O
.	O
</s>
<s>
It	O
was	O
certainly	O
enough	O
to	O
write	O
FORTRAN	B-Application
,	O
or	O
print	O
financial	O
or	O
scientific	O
reports	O
.	O
</s>
<s>
There	O
were	O
actually	O
two	O
variations	O
of	O
the	O
CDC	B-Application
display	I-Application
code	I-Application
character	O
sets	O
in	O
use	O
—	O
64-character	O
and	O
63-character	O
.	O
</s>
<s>
A	O
complementary	O
variant	O
,	O
called	O
6/12	O
display	B-Application
code	I-Application
,	O
was	O
also	O
used	O
in	O
the	O
Kronos	B-Operating_System
and	O
NOS	B-Operating_System
timesharing	B-General_Concept
systems	O
to	O
allow	O
full	O
use	O
of	O
the	O
ASCII	B-Protocol
character	I-Protocol
set	I-Protocol
in	O
a	O
manner	O
somewhat	O
compatible	O
with	O
older	O
software	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
CDC	O
COBOL	B-Application
compiler	O
was	O
actually	O
quite	O
good	O
at	O
processing	O
decimal	O
fields	O
using	O
this	O
technique	O
.	O
</s>
<s>
The	O
chassis	O
were	O
numbered	O
from	O
1	O
(	O
containing	O
all	O
10	O
PPUs	O
and	O
their	O
memories	O
,	O
as	O
well	O
as	O
the	O
12	O
rather	O
minimal	O
I/O	B-Device
channels	I-Device
)	O
to	O
16	O
.	O
</s>
<s>
The	O
module	O
consisted	O
of	O
two	O
parallel	B-Operating_System
printed	O
circuit	O
boards	O
,	O
with	O
components	O
mounted	O
either	O
on	O
one	O
of	O
the	O
boards	O
or	O
between	O
the	O
two	O
boards	O
.	O
</s>
<s>
There	O
was	O
a	O
sore	O
point	O
with	O
the	O
6600	O
operating	B-General_Concept
system	I-General_Concept
support	O
—	O
slipping	O
timelines	O
.	O
</s>
<s>
The	O
machines	O
originally	O
ran	O
a	O
very	O
simple	O
job-control	B-General_Concept
system	O
known	O
as	O
COS	O
(	O
Chippewa	B-Operating_System
Operating	I-Operating_System
System	I-Operating_System
)	O
,	O
which	O
was	O
quickly	O
"	O
thrown	O
together	O
"	O
based	O
on	O
the	O
earlier	O
CDC	B-Device
3000	I-Device
operating	B-General_Concept
system	I-General_Concept
in	O
order	O
to	O
have	O
something	O
running	O
to	O
test	O
the	O
systems	O
for	O
delivery	O
.	O
</s>
<s>
However	O
the	O
machines	O
were	O
intended	O
to	O
be	O
delivered	O
with	O
a	O
much	O
more	O
powerful	O
system	O
known	O
as	O
SIPROS	O
(	O
for	O
Simultaneous	O
Processing	O
Operating	B-General_Concept
System	I-General_Concept
)	O
,	O
which	O
was	O
being	O
developed	O
at	O
the	O
company	O
's	O
System	O
Sciences	O
Division	O
in	O
Los	O
Angeles	O
.	O
</s>
<s>
Operating	B-General_Concept
system	I-General_Concept
development	O
then	O
split	O
into	O
two	O
camps	O
.	O
</s>
<s>
Many	O
customers	O
eventually	O
took	O
delivery	O
of	O
their	O
systems	O
with	O
this	O
software	O
,	O
then	O
known	O
as	O
SCOPE	B-Operating_System
(	O
Supervisory	O
Control	O
Of	O
Program	O
Execution	O
)	O
.	O
</s>
<s>
SCOPE	B-Operating_System
version	O
1	O
was	O
,	O
essentially	O
,	O
dis-assembled	O
COS	O
;	O
SCOPE	B-Operating_System
version	O
2	O
included	O
new	O
device	O
and	O
file	O
system	O
support	O
;	O
SCOPE	B-Operating_System
version	O
3	O
included	O
permanent	O
file	O
support	O
,	O
EI/200	O
remote	O
batch	O
support	O
,	O
and	O
INTERCOM	O
time-sharing	B-General_Concept
support	O
.	O
</s>
<s>
SCOPE	B-Operating_System
always	O
had	O
significant	O
reliability	O
and	O
maintainability	O
issues	O
.	O
</s>
<s>
Its	O
feature	O
set	O
was	O
essentially	O
the	O
same	O
as	O
COS	O
and	O
SCOPE	B-Operating_System
1	O
.	O
</s>
<s>
The	O
unofficial	O
MACE	O
software	O
was	O
later	O
chosen	O
over	O
the	O
official	O
SCOPE	B-Operating_System
product	O
as	O
the	O
basis	O
of	O
the	O
next	O
CDC	O
operating	B-General_Concept
system	I-General_Concept
,	O
Kronos	B-Operating_System
,	O
named	O
after	O
the	O
Greek	B-Application
god	I-Application
of	I-Application
time	I-Application
.	O
</s>
<s>
He	O
wrote	O
down	O
"	O
Kronos	B-Operating_System
"	O
instead	O
of	O
"	O
Chronos	B-Application
"	O
.	O
</s>
<s>
The	O
main	O
marketing	O
reason	O
for	O
its	O
adoption	O
was	O
the	O
development	O
of	O
its	O
TELEX	O
time-sharing	B-General_Concept
feature	O
and	O
its	O
BATCHIO	O
remote	O
batch	O
feature	O
.	O
</s>
<s>
Kronos	B-Operating_System
continued	O
to	O
use	O
the	O
COS/SCOPE	O
1	O
file	O
system	O
with	O
the	O
addition	O
of	O
a	O
permanent	O
file	O
feature	O
.	O
</s>
<s>
An	O
attempt	O
to	O
unify	O
the	O
SCOPE	B-Operating_System
and	O
Kronos	B-Operating_System
operating	B-General_Concept
system	I-General_Concept
products	O
produced	O
NOS	B-Operating_System
,	O
(	O
Network	O
Operating	B-General_Concept
System	I-General_Concept
)	O
.	O
</s>
<s>
NOS	B-Operating_System
was	O
intended	O
to	O
be	O
the	O
sole	O
operating	B-General_Concept
system	I-General_Concept
for	O
all	O
CDC	O
machines	O
,	O
a	O
fact	O
CDC	O
promoted	O
heavily	O
.	O
</s>
<s>
Many	O
SCOPE	B-Operating_System
customers	O
remained	O
software-dependent	O
on	O
the	O
SCOPE	B-Operating_System
architecture	B-General_Concept
,	O
so	O
CDC	O
simply	O
renamed	O
it	O
NOS/BE	B-Operating_System
(	O
Batch	O
Environment	O
)	O
,	O
and	O
were	O
able	O
to	O
claim	O
that	O
everyone	O
was	O
thus	O
running	O
NOS	B-Operating_System
.	O
</s>
<s>
In	O
practice	O
,	O
it	O
was	O
far	O
easier	O
to	O
modify	O
the	O
Kronos	B-Operating_System
code	O
base	O
to	O
add	O
SCOPE	B-Operating_System
features	O
than	O
the	O
reverse	O
.	O
</s>
<s>
The	O
assembly	O
plant	O
environment	O
also	O
produced	O
other	O
operating	B-General_Concept
systems	I-General_Concept
which	O
were	O
never	O
intended	O
for	O
customer	O
use	O
.	O
</s>
<s>
The	O
names	O
SCOPE	B-Operating_System
and	O
COMPASS	B-Language
were	O
used	O
by	O
CDC	O
for	O
both	O
the	O
CDC	B-Device
6000	I-Device
series	I-Device
,	O
including	O
the	O
6600	O
,	O
and	O
the	O
CDC	B-Device
3000	I-Device
series	I-Device
:	O
</s>
<s>
The	O
name	O
COMPASS	B-Language
was	O
used	O
by	O
CDC	O
for	O
the	O
Assembly	B-Language
languages	I-Language
on	O
both	O
families	O
.	O
</s>
<s>
The	O
name	O
SCOPE	B-Operating_System
was	O
used	O
for	O
its	O
implementations	O
on	O
the	O
3000	O
and	O
6000	B-Device
series	I-Device
.	O
</s>
<s>
The	O
CDC	B-Device
7600	I-Device
was	O
originally	O
intended	O
to	O
be	O
fully	O
compatible	O
with	O
the	O
existing	O
6000-series	O
machines	O
as	O
well	O
;	O
it	O
started	O
life	O
known	O
as	O
the	O
CDC	O
6800	O
.	O
</s>
<s>
While	O
the	O
CDC	B-Device
7600	I-Device
's	O
CPU	O
was	O
basically	O
instruction	O
compatible	O
with	O
the	O
6400	O
and	O
6600	O
CPUs	O
,	O
allowing	O
code	O
portability	O
at	O
the	O
high-level	B-Language
language	I-Language
source	O
code	O
level	O
,	O
the	O
CDC	B-Device
7600	I-Device
's	O
hardware	O
,	O
especially	O
that	O
of	O
its	O
Peripheral	O
Processor	O
Units	O
(	O
PPUs	O
)	O
,	O
was	O
quite	O
different	O
,	O
and	O
the	O
CDC	B-Device
7600	I-Device
required	O
a	O
different	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
Unlike	O
the	O
6600	O
CPU	O
,	O
the	O
CDC	B-Device
7600	I-Device
's	O
CPU	O
could	O
control	O
its	O
own	O
operation	O
via	O
a	O
Central	O
Exchange	O
jump	O
(	O
XJ	O
)	O
instruction	O
that	O
swapped	O
all	O
register	O
contents	O
with	O
core	O
memory	O
.	O
</s>
