<s>
The	O
first	O
machines	O
in	O
the	O
series	O
are	O
the	O
16-bit	B-Device
Sigma	O
2	O
and	O
the	O
32-bit	O
Sigma	O
7	O
;	O
the	O
Sigma	O
7	O
was	O
the	O
first	O
32-bit	O
computer	O
released	O
by	O
SDS	O
.	O
</s>
<s>
At	O
the	O
time	O
,	O
the	O
only	O
competition	O
for	O
the	O
Sigma	O
7	O
was	O
the	O
IBM	B-Application
360	I-Application
.	O
</s>
<s>
For	O
example	O
,	O
the	O
Sigma	O
5	O
base	O
memory	O
is	O
16K	O
32-Bit	O
words	O
(	O
64K	O
Bytes	B-Application
)	O
.	O
</s>
<s>
Maximum	O
memory	O
is	O
limited	O
by	O
the	O
length	O
of	O
the	O
instruction	O
address	O
field	O
of	O
17	O
bits	O
,	O
or	O
128K	O
Words	O
(	O
512K	O
Bytes	B-Application
)	O
.	O
</s>
<s>
The	O
Xerox	B-Device
500	I-Device
series	I-Device
computers	O
,	O
introduced	O
starting	O
in	O
1973	O
,	O
are	O
compatible	O
upgrades	O
to	O
the	O
Sigma	O
systems	O
using	O
newer	O
technology	O
.	O
</s>
<s>
Keith	O
Calkins	O
made	O
the	O
Sigma	O
9	O
functional	O
for	O
the	O
museum	O
in	O
2012/13	O
and	O
brought	O
up	O
the	O
CP-V	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
in	O
Dec	O
.	O
2014	O
.	O
</s>
<s>
Model	O
Date	O
Floating	O
point	O
Decimal	O
Byte	B-Application
string	O
Memory	O
map	O
Max	O
memory	O
(	O
kwords	O
)	O
Sigma	O
7	O
1966	O
optional	O
optional	O
standard	O
optional	O
128	O
Sigma	O
5	O
1967	O
optional	O
N/A	O
N/A	O
N/A	O
128	O
Sigma	O
6	O
1970	O
optional	O
standard	O
standard	O
standard	O
128	O
Sigma	O
9	O
1971	O
standard	O
standard	O
standard	O
standard	O
512	O
Sigma	O
8	O
1972	O
standard	O
N/A	O
N/A	O
N/A	O
128	O
Sigma	O
9	O
model	O
2	O
?	O
</s>
<s>
If	O
the	O
high-order	O
bit	O
is	O
0	O
,	O
the	O
lower	O
16	B-Device
bits	I-Device
of	O
the	O
address	O
refer	O
to	O
a	O
location	O
in	O
the	O
first	O
64K	O
words	O
of	O
main	O
memory	O
;	O
if	O
the	O
high-order	O
bit	O
is	O
1	O
,	O
the	O
lower	O
16	B-Device
bits	I-Device
of	O
the	O
address	O
refer	O
to	O
a	O
location	O
in	O
a	O
64K-word	O
block	O
of	O
memory	O
specified	O
by	O
the	O
Extension	O
Address	O
in	O
bits	O
42-47	O
of	O
the	O
Program	O
Status	O
Doubleword	O
,	O
with	O
the	O
Extension	O
Address	O
being	O
concatenated	O
with	O
the	O
lower	O
16	B-Device
bits	I-Device
of	O
the	O
reference	O
address	O
to	O
form	O
the	O
physical	O
address	O
.	O
</s>
<s>
Memory	O
in	O
the	O
Sigma	O
systems	O
can	O
be	O
addressed	O
as	O
individual	O
bytes	B-Application
,	O
halfwords	O
,	O
words	O
,	O
or	O
doublewords	O
.	O
</s>
<s>
All	O
32-bit	O
Sigma	O
systems	O
except	O
the	O
Sigma	O
5	O
and	O
Sigma	O
8	O
used	O
a	O
memory	O
map	O
to	O
implement	O
virtual	B-Architecture
memory	I-Architecture
.	O
</s>
<s>
Otherwise	O
,	O
in	O
virtual	B-Architecture
memory	I-Architecture
mode	O
the	O
high-order	O
eight	O
bits	O
of	O
an	O
address	O
,	O
called	O
virtual	O
page	O
number	O
,	O
are	O
used	O
as	O
an	O
index	O
to	O
an	O
array	O
of	O
256	O
13-bit	O
memory	O
map	O
registers	O
.	O
</s>
<s>
Input/output	O
is	O
accomplished	O
using	O
a	O
control	B-General_Concept
unit	I-General_Concept
called	O
an	O
IOP	O
(	O
Input-output	O
processor	O
)	O
.	O
</s>
<s>
The	O
SIOP	O
provides	O
a	O
data	O
rate	O
up	O
to	O
1.5	O
megabytes	B-Application
per	O
second	O
(	O
MBPS	O
)	O
,	O
but	O
allows	O
only	O
one	O
device	O
to	O
be	O
active	O
at	O
a	O
time	O
.	O
</s>
<s>
The	O
primary	O
mass	O
storage	O
device	O
,	O
known	O
as	O
a	O
RAD	O
(	O
random-access	B-General_Concept
disk	O
)	O
,	O
contains	O
512	O
fixed	O
heads	O
and	O
a	O
large	O
(	O
approx	O
600mm/24in	O
diameter	O
)	O
vertically	O
mounted	O
disk	O
spinning	O
at	O
relatively	O
low	O
speeds	O
.	O
</s>
<s>
Capacities	O
range	O
from	O
1.6	O
to	O
6.0	O
megabytes	B-Application
and	O
are	O
used	O
for	O
temporary	O
storage	O
.	O
</s>
<s>
The	O
System	O
Control	B-General_Concept
Unit	I-General_Concept
(	O
SCU	O
)	O
was	O
a	O
"	O
microprogrammable	B-Device
data	O
processor	O
"	O
which	O
can	O
interface	O
to	O
a	O
Sigma	O
CPU	O
,	O
and	O
"	O
to	O
peripheral	O
and	O
analog	O
devices	O
,	O
and	O
to	O
many	O
kinds	O
of	O
line	O
protocol.	O
"	O
</s>
<s>
The	O
SCU	O
executes	O
horizontal	O
microinstructions	B-Device
with	O
a	O
32-bit	O
word	O
length	O
.	O
</s>
<s>
A	O
cross-assembler	O
running	O
on	O
a	O
Sigma	O
system	O
can	O
be	O
used	O
to	O
create	O
microprograms	B-Device
for	O
the	O
SCU	O
.	O
</s>
<s>
The	O
Sigma	O
5	O
sold	O
for	O
US$	O
300,000	O
with	O
16	O
kilowords	O
of	O
random-access	B-General_Concept
magnetic-core	O
memory	O
,	O
with	O
an	O
optional	O
memory	O
upgrade	O
to	O
32kW	O
for	O
an	O
additional	O
$	O
50,000	O
.	O
</s>
<s>
The	O
hard	B-Device
disk	I-Device
drive	I-Device
had	O
a	O
capacity	O
of	O
3	O
megabytes	B-Application
.	O
</s>
<s>
The	O
Universal	B-Operating_System
Time-Sharing	I-Operating_System
System	I-Operating_System
(	O
UTS	O
)	O
became	O
available	O
in	O
1971	O
,	O
supporting	O
much	O
enhanced	O
time-sharing	O
facilities	O
.	O
</s>
<s>
A	O
compatible	O
upgrade	O
(	O
or	O
renaming	O
)	O
of	O
UTS	O
,	O
Control	O
Program	O
V	O
(	O
CP-V	B-Operating_System
)	O
became	O
available	O
starting	O
in	O
1973	O
and	O
added	O
real-time	O
,	O
remote	O
batch	O
,	O
and	O
transaction	O
processing	O
.	O
</s>
<s>
The	O
Xerox	B-Operating_System
Operating	I-Operating_System
System	I-Operating_System
(	O
XOS	O
)	O
,	O
intended	O
as	O
an	O
IBM	O
DOS/360	O
replacement	O
(	O
not	O
to	O
be	O
confused	O
with	O
PC	B-Operating_System
DOS	I-Operating_System
of	O
a	O
latter	O
era	O
)	O
,	O
also	O
runs	O
on	O
Sigma	O
6/7/9	O
systems	O
,	O
but	O
never	O
gained	O
real	O
popularity	O
.	O
</s>
<s>
The	O
Xerox	O
software	O
,	O
called	O
processors	O
,	O
available	O
for	O
CP-V	B-Operating_System
in	O
1978	O
included	O
:	O
</s>
