<s>
The	O
CDC	B-Device
7600	I-Device
was	O
the	O
Seymour	O
Cray-designed	O
successor	O
to	O
the	O
CDC	B-Device
6600	I-Device
,	O
extending	O
Control	O
Data	O
's	O
dominance	O
of	O
the	O
supercomputer	B-Architecture
field	O
into	O
the	O
1970s	O
.	O
</s>
<s>
The	O
7600	O
ran	O
at	O
36.4MHz	O
(	O
27.5ns	O
clock	O
cycle	O
)	O
and	O
had	O
a	O
65	O
Kword	O
primary	O
memory	O
(	O
with	O
a	O
60-bit	B-Device
word	O
size	O
)	O
using	O
magnetic	O
core	O
and	O
variable-size	O
(	O
up	O
to	O
512	O
Kword	O
)	O
secondary	O
memory	O
(	O
depending	O
on	O
site	O
)	O
.	O
</s>
<s>
It	O
was	O
generally	O
about	O
ten	O
times	O
as	O
fast	O
as	O
the	O
CDC	B-Device
6600	I-Device
and	O
could	O
deliver	O
about	O
10	O
MFLOPS	O
on	O
hand-compiled	O
code	O
,	O
with	O
a	O
peak	O
of	O
36	O
MFLOPS	O
.	O
</s>
<s>
In	O
addition	O
,	O
in	O
benchmark	O
tests	O
in	O
early	O
1970	O
it	O
was	O
shown	O
to	O
be	O
slightly	O
faster	O
than	O
its	O
IBM	O
rival	O
,	O
the	O
IBM	B-Application
System/360	I-Application
,	O
Model	O
195	O
.	O
</s>
<s>
Among	O
the	O
7600	O
's	O
notable	O
state-of-the-art	O
contributions	O
,	O
beyond	O
extensive	O
pipelining	B-General_Concept
,	O
was	O
the	O
physical	O
C-shape	O
,	O
which	O
both	O
reduced	O
floor	O
space	O
and	O
dramatically	O
increased	O
performance	O
by	O
reducing	O
the	O
distance	O
that	O
signals	O
needed	O
to	O
travel	O
.	O
</s>
<s>
Transistors	B-Application
in	O
general	O
were	O
also	O
getting	O
somewhat	O
faster	O
as	O
the	O
production	O
processes	O
and	O
quality	O
improved	O
.	O
</s>
<s>
In	O
order	O
to	O
solve	O
this	O
problem	O
,	O
Cray	O
turned	O
to	O
the	O
concept	O
of	O
an	O
instruction	B-General_Concept
pipeline	I-General_Concept
.	O
</s>
<s>
For	O
instance	O
,	O
the	O
6600	O
's	O
multiply	O
unit	O
took	O
10	O
cycles	O
to	O
complete	O
an	O
instruction	O
,	O
so	O
by	O
pipelining	B-General_Concept
the	O
units	O
it	O
could	O
be	O
expected	O
to	O
gain	O
about	O
10	O
times	O
the	O
speed	O
.	O
</s>
<s>
Pipelining	B-General_Concept
requires	O
that	O
the	O
unit	O
's	O
internals	O
can	O
be	O
effectively	O
separated	O
to	O
the	O
point	O
where	O
each	O
step	O
of	O
the	O
operation	O
is	O
running	O
on	O
completely	O
separate	O
circuitry	O
.	O
</s>
<s>
Nevertheless	O
,	O
the	O
use	O
of	O
pipelining	B-General_Concept
on	O
the	O
7600	O
improved	O
performance	O
over	O
the	O
6600	O
by	O
a	O
factor	O
of	O
about	O
3	O
.	O
</s>
<s>
To	O
achieve	O
the	O
rest	O
of	O
the	O
goal	O
,	O
the	O
machine	O
would	O
have	O
to	O
run	O
at	O
a	O
faster	O
speed	O
,	O
now	O
possible	O
using	O
new	O
transistor	B-Application
designs	O
.	O
</s>
<s>
For	O
the	O
7600	O
,	O
each	O
circuit	O
module	O
actually	O
consisted	O
of	O
up	O
to	O
six	O
printed	O
circuit	O
boards	O
,	O
each	O
one	O
stuffed	O
with	O
subminiature	O
resistors	O
,	O
diodes	O
,	O
and	O
transistors	B-Application
.	O
</s>
<s>
It	O
is	O
a	O
reduced-instruction-set	B-Architecture
computer	I-Architecture
with	O
a	O
15-bit	O
instruction	O
word	O
containing	O
a	O
6-bit	O
operation	O
code	O
.	O
</s>
<s>
There	O
are	O
only	O
64	O
machine	O
codes	O
,	O
including	O
a	O
no-operation	B-Language
code	I-Language
,	O
with	O
no	O
fixed-point	O
multiply	O
or	O
divide	O
operations	O
in	O
the	O
central	O
processor	O
.	O
</s>
<s>
It	O
has	O
an	O
access	O
time	O
of	O
10	O
of	O
the	O
27.5-ns	O
minor	O
cycles	O
and	O
a	O
60-bit	B-Device
word	O
length	O
.	O
</s>
<s>
On	O
an	O
operating	B-General_Concept
system	I-General_Concept
call	O
,	O
the	O
contents	O
of	O
the	O
small	O
core	O
memory	O
are	O
swapped	O
out	O
and	O
replaced	O
from	O
the	O
large	O
core	O
memory	O
by	O
the	O
operating	B-General_Concept
system	I-General_Concept
,	O
and	O
restored	O
afterward	O
.	O
</s>
<s>
There	O
is	O
a	O
12-word	O
instruction	B-General_Concept
pipeline	I-General_Concept
,	O
called	O
instruction	O
word	O
stack	O
in	O
CDC	O
documentation	O
.	O
</s>
<s>
There	O
are	O
eight	O
60-bit	B-Device
registers	O
,	O
each	O
with	O
an	O
address	O
register	O
.	O
</s>
<s>
The	O
programmer	O
or	O
compiler	B-Language
tries	O
to	O
fetch	O
data	O
in	O
time	O
to	O
be	O
used	O
and	O
store	O
data	O
before	O
more	O
data	O
needs	O
the	O
same	O
register	O
,	O
but	O
if	O
it	O
is	O
not	O
ready	O
,	O
the	O
processor	O
goes	O
into	O
a	O
wait	O
state	O
until	O
it	O
is	O
.	O
</s>
<s>
It	O
also	O
waits	O
if	O
one	O
of	O
the	O
four	O
floating-point	O
arithmetic	O
units	O
is	O
not	O
ready	O
when	O
requested	O
,	O
but	O
due	O
to	O
pipelining	B-General_Concept
,	O
this	O
does	O
not	O
usually	O
happen	O
.	O
</s>
<s>
The	O
CDC	B-Device
7600	I-Device
"	O
was	O
designed	O
to	O
be	O
machine	O
code	O
upward	B-General_Concept
compatible	I-General_Concept
with	O
the	O
6600	O
,	O
but	O
to	O
provide	O
a	O
substantial	O
increase	O
in	O
performance	O
"	O
.	O
</s>
<s>
Although	O
the	O
7600	O
shared	O
many	O
features	O
of	O
the	O
6600	O
,	O
including	O
hardware	O
,	O
instructions	O
,	O
and	O
its	O
60-bit	B-Device
word	O
size	O
,	O
it	O
was	O
not	O
object-code	O
compatible	B-General_Concept
with	O
the	O
CDC	B-Device
6600	I-Device
.	O
</s>
<s>
In	O
addition	O
,	O
it	O
was	O
not	O
entirely	O
source-code	O
(	O
COMPASS	B-Language
)	O
compatible	B-General_Concept
,	O
as	O
some	O
instructions	O
in	O
the	O
7600	O
did	O
not	O
exist	O
in	O
the	O
6600	O
,	O
and	O
vice	O
versa	O
.	O
</s>
<s>
It	O
had	O
originally	O
been	O
named	O
the	O
CDC	O
6800	O
,	O
but	O
was	O
changed	O
to	O
7600	O
when	O
Cray	O
decided	O
that	O
it	O
could	O
not	O
be	O
completely	O
compatible	B-General_Concept
.	O
</s>
<s>
However	O
,	O
due	O
to	O
the	O
7600	O
's	O
operating	B-General_Concept
system	I-General_Concept
design	O
,	O
the	O
6600	O
and	O
7600	O
shared	O
a	O
"	O
uniform	O
software	O
environment	O
"	O
despite	O
the	O
low-level	O
differences	O
.	O
</s>
<s>
In	O
order	O
to	O
take	O
advantage	O
of	O
this	O
,	O
the	O
6600	O
and	O
7600	O
left	O
mundane	O
housekeeping	O
tasks	O
,	O
printing	O
output	O
or	O
reading	O
punched	B-Architecture
cards	I-Architecture
,	O
for	O
instance	O
,	O
to	O
a	O
series	O
of	O
ten	O
smaller	O
12-bit	O
machines	O
based	O
on	O
the	O
CDC	B-Device
160-A	I-Device
known	O
as	O
"	O
Peripheral	O
Processor	O
Units	O
"	O
,	O
or	O
PPUs	O
.	O
</s>
<s>
Like	O
the	O
6600	O
,	O
the	O
7600	O
used	O
60-bit	B-Device
words	O
with	O
instructions	O
that	O
were	O
generally	O
15	O
bits	O
in	O
length	O
,	O
although	O
there	O
were	O
also	O
30-bit	O
instructions	O
.	O
</s>
<s>
The	O
instructions	O
were	O
packed	O
into	O
the	O
60-bit	B-Device
words	O
,	O
but	O
a	O
30-bit	O
instruction	O
could	O
not	O
straddle	O
two	O
words	O
,	O
and	O
control	O
could	O
only	O
be	O
transferred	O
to	O
the	O
first	O
instruction	O
in	O
a	O
word	O
.	O
</s>
<s>
The	O
machines	O
were	O
similar	O
enough	O
to	O
make	O
porting	O
of	O
compilers	B-Language
and	O
operating	B-General_Concept
systems	I-General_Concept
possible	O
without	O
too	O
much	O
trouble	O
.	O
</s>
<s>
The	O
machine	O
initially	O
did	O
not	O
come	O
with	O
software	O
;	O
sites	O
had	O
to	O
be	O
willing	O
to	O
write	O
their	O
own	O
operating	B-General_Concept
system	I-General_Concept
,	O
like	O
LTSS	O
,	O
NCAROS	O
,	O
and	O
others	O
;	O
and	O
compilers	B-Language
like	O
LRLTRAN	O
(	O
Livermore	O
's	O
version	O
of	O
Fortran	O
with	O
dynamic	O
memory	O
management	O
and	O
other	O
non-standard	O
features	O
)	O
.	O
</s>
<s>
From	O
about	O
1969	O
to	O
1975	O
,	O
the	O
CDC	B-Device
7600	I-Device
was	O
generally	O
regarded	O
as	O
the	O
fastest	O
computer	O
in	O
the	O
world	O
,	O
except	O
for	O
specialized	O
units	O
.	O
</s>
<s>
The	O
successor	O
CDC	B-Device
8600	I-Device
was	O
never	O
completed	O
,	O
and	O
Seymour	O
Cray	O
went	O
on	O
to	O
form	O
his	O
own	O
company	O
,	O
Cray	O
Research	O
.	O
</s>
